foxtrot/generic_loader/load_sas.py

"""Per-file SAS-to-Postgres loader.

Library-style functions plus a thin CLI wrapper. Designed so an orchestrator
can wrap the library for directory/batch mode; orchestration is out of scope
here.

Python 3.14 compatible (target is an air-gapped host that currently only has
3.14). ``from __future__ import annotations`` lets us use PEP 585 generics
as annotations; runtime-resolved type uses (dataclass defaults, etc.) stick
to ``typing``.

-------------------------------------------------------------------------------
USAGE
-------------------------------------------------------------------------------

Supported inputs:
    * ``.sas7bdat`` (read with ``encoding="latin-1"``)
    * ``.xpt`` / ``.xport`` (SAS transport files)

1. YAML config
--------------
Every invocation is driven by a YAML file describing one SAS file to load::

    filename: samples/sample_kitchensink.xpt   # required; relative paths are
                                               # resolved against the config
                                               # file's directory when possible
    schemaname: public                         # required
    tablename:  kitchensink                    # required

    # Optional. One of: fail | replace | append. Default: fail.
    #   fail    - error out if the target table already exists
    #   replace - DROP and recreate the table from the inferred schema
    #   append  - keep the existing table; pre-flight a schema-compat check,
    #             then COPY the new rows in
    if_exists: append

    # Optional, mutually exclusive. Restrict which columns are loaded.
    # include:
    #   - ID
    #   - INTCOL
    # exclude:
    #   - ALLNULL

2. Database connection
----------------------
The loader uses standard libpq environment variables (read via ``os.environ``)::

    PGHOST, PGPORT, PGUSER, PGPASSWORD, PGDATABASE

The CLI calls ``python-dotenv``'s ``load_dotenv()`` at startup, so a local
``.env`` file is picked up automatically. Library callers are responsible for
populating the environment themselves (either call ``load_dotenv()`` or export
the vars) before calling :func:`connect`.

3. Command-line interface
-------------------------
::

    python load_sas.py --config path/to/config.yaml [--validate] [--dry-run]
                       [--dbcreds]

Flags:
    --config PATH   Required. Path to the YAML config above.
    --validate      Compare the inferred schema against
                    ``<sas-file-stem>.expected.json`` sitting next to the SAS
                    file. Exits nonzero on mismatch. Safe to combine with
                    ``--dry-run``.
    --dry-run       Print the inferred ``CREATE TABLE`` SQL and stop. The
                    database is never touched (no connection is opened).
    --dbcreds       Prompt interactively for the database username and
                    password instead of reading ``PGUSER`` / ``PGPASSWORD``
                    from the environment or ``.env`` file. The password
                    prompt does not echo. Has no effect with ``--dry-run``
                    (no connection is opened).

Exit codes:
    0 - success (load completed, or dry-run/validate passed)
    1 - validation failure
    2 - config references a SAS file that does not exist
    Other nonzero - uncaught exception (traceback printed); the transaction
    is rolled back before exit.

Typical invocations::

    # Preview the inferred schema without connecting to Postgres.
    python load_sas.py --config sample_config.yaml --dry-run

    # Check the inferred schema against an expected-types manifest.
    python load_sas.py --config sample_config.yaml --validate --dry-run

    # Actually load the data.
    python load_sas.py --config sample_config.yaml

    # Load the data, prompting for credentials instead of using .env.
    python load_sas.py --config sample_config.yaml --dbcreds

4. Expected-types manifest (``--validate``)
-------------------------------------------
``--validate`` looks for a JSON file named ``<sas-stem>.expected.json`` next
to the SAS file, e.g. ``samples/sample_kitchensink.xpt`` pairs with
``samples/sample_kitchensink.expected.json``. Each top-level key is a column
name; the value is an object with any of::

    {
        "postgres_type": "BIGINT",        # exact expected type, OR
        "acceptable_types": ["TEXT",      # any-of list of acceptable types
                             "VARCHAR"],
        "nullable": true,                 # default true; false = must be NOT NULL
        "note": "free-form comment"       # ignored by the loader
    }

Type comparison ignores length/precision modifiers and normalizes synonyms
(e.g. ``INT`` == ``INTEGER`` == ``INT4``; ``VARCHAR(10)`` == ``VARCHAR``).
Nullability tightening (inferred NULL, manifest NOT NULL) is a hard failure;
loosening is not checked here because the append-mode check already covers it.

5. Library usage
----------------
The CLI is a thin wrapper around composable functions. The preferred pattern
infers the schema from a bounded preview and then streams the rest of the
file chunk-by-chunk into ``COPY`` - crucial for SAS files with hundreds of
millions of rows::

    from dotenv import load_dotenv
    from load_sas import (
        load_config, read_sas_preview, iter_sas_chunks, apply_column_filter,
        infer_schema, validate_against_manifest, render_create_table,
        connect, create_table, copy_dataframes,
    )

    load_dotenv()
    cfg = load_config("config.yaml")

    # Schema from a preview slice (bounded by TYPE_INFERENCE_SAMPLE_ROWS).
    preview_df, meta = read_sas_preview(cfg.filename)
    preview_df = apply_column_filter(preview_df, cfg.include, cfg.exclude)
    total_rows = getattr(meta, "number_rows", None)
    columns = infer_schema(preview_df, meta, total_rows=total_rows)

    # Optional: preview DDL / validate against a manifest.
    print(render_create_table(cfg.schemaname, cfg.tablename, columns))
    problems = validate_against_manifest(columns, Path("expected.json"))
    assert not problems, problems

    conn = connect()
    conn.autocommit = False
    try:
        create_table(conn, cfg.schemaname, cfg.tablename, columns, cfg.if_exists)
        chunks = (
            apply_column_filter(df, cfg.include, cfg.exclude)
            for df, _ in iter_sas_chunks(cfg.filename)
        )
        rows = copy_dataframes(conn, cfg.schemaname, cfg.tablename, chunks, columns)
        conn.commit()
    finally:
        conn.close()

For small files (or tests) the legacy one-shot API still works:
:func:`read_sas` returns the whole frame and :func:`copy_dataframe` copies it
in one round trip.

All functions are side-effect free except :func:`connect`, :func:`create_table`,
:func:`copy_dataframe`, and :func:`copy_dataframes`; schema inference
(:func:`infer_schema`) accepts a ``coerce_chars`` kwarg to override the
module-level ``COERCE_CHAR_COLUMNS`` without mutating global state.

6. Type inference summary
-------------------------
Priority order used by :func:`infer_schema`:

    1. SAS format string (via ``meta.original_variable_types``):
       ``DATETIME*`` -> ``TIMESTAMP``, ``TIME*`` -> ``TIME``,
       ``DATE*`` / ``YYMMDD*`` / ``MMDDYY*`` / ``DDMMYY*`` / ``JULIAN*`` -> ``DATE``.
    2. All-null column -> ``TEXT`` (with a note).
    3. pandas datetime dtype -> ``TIMESTAMP``.
    4. Object columns containing only ``datetime.date`` / ``datetime.datetime``
       -> ``DATE`` or ``TIMESTAMP``.
    5. Object columns of strings: if ``COERCE_CHAR_COLUMNS`` is True and at
       least ``CHAR_INFERENCE_MIN_VALUES`` non-empty values parse cleanly, they
       are promoted to ``INTEGER`` / ``BIGINT`` / ``DOUBLE PRECISION`` /
       ``DATE`` / ``TIMESTAMP``; otherwise ``TEXT``.
    6. Numeric columns of whole numbers -> ``INTEGER`` (or ``BIGINT`` if any
       value exceeds the int32 range ``NUMERIC_INT_RANGE``); otherwise
       ``DOUBLE PRECISION``.

Type inference scans the whole file by default (``TYPE_INFERENCE_SAMPLE_ROWS
= None``) so type + nullability are both computed against every row. The CLI
materializes the file once for schema inference, then re-streams it chunk by
chunk into ``COPY``; peak memory is roughly one full dataframe. Override
``TYPE_INFERENCE_SAMPLE_ROWS`` to an integer cap if you're on a host that
can't hold the file in memory - but know that sampled specs carry the usual
risks: a later row may exceed the inferred integer range, or a column that
had no nulls in the preview may carry nulls later in the file (which then
detonates ``COPY`` because the sampled spec stamped it ``NOT NULL``). Seen
in production on a 2.5M-row file with ~6k null MAFIDs past the 10k-row
preview - the entire load aborted mid-stream.

Streaming loads use :func:`iter_sas_chunks` + :func:`copy_dataframes`, which
commit each chunk as it is copied so an interrupted load retains the rows
that were already written.

7. Tunables
-----------
Module-level knobs at the top of this file:

    * ``COERCE_CHAR_COLUMNS``         - promote stringly-typed numerics / dates
                                        (default True).
    * ``CHAR_INFERENCE_MIN_VALUES``    - minimum non-empty sample size before
                                        char-column coercion is attempted.
    * ``NUMERIC_INT_RANGE``            - INTEGER bounds; values outside become
                                        ``BIGINT``.
    * ``TYPE_INFERENCE_SAMPLE_ROWS``   - cap on rows read for type inference
                                        (``None`` = scan the whole column).
    * ``DEFAULT_CHUNK_ROWS``           - rows per streaming COPY chunk.
"""

from __future__ import annotations

import argparse
import datetime as dt
import getpass
import hashlib
import io
import json
import logging
import math
import os
import re
import sys
from dataclasses import dataclass, field
from pathlib import Path
from typing import Any, Dict, Iterable, List, Optional, Tuple

import pandas as pd
import psycopg2
import psycopg2.extensions
import pyarrow as pa
import pyarrow.csv as pa_csv
import pyreadstat
import yaml
from dotenv import load_dotenv
from tqdm import tqdm


logger = logging.getLogger(__name__)


# ---------------------------------------------------------------------------
# Top-level tunables
# ---------------------------------------------------------------------------

COERCE_CHAR_COLUMNS = True
"""If True, try to promote object (string) columns to numeric/date/timestamp
when every non-empty value parses cleanly."""

CHAR_INFERENCE_MIN_VALUES = 3
"""Don't attempt character-column coercion with fewer than this many non-empty
values; too small a sample is easy to mis-infer."""

NUMERIC_INT_RANGE = (-2_147_483_648, 2_147_483_647)
"""INTEGER bounds; anything outside becomes BIGINT."""

TYPE_INFERENCE_SAMPLE_ROWS: Optional[int] = None
"""Cap on rows inspected during per-column type inference. Also governs how
many rows :func:`read_sas_preview` pulls from the file for dry-run / validate /
schema-inference flows.

Default is ``None`` (scan every row, reading the whole file into memory for
the schema-inference step). That's the only honest setting for nullability:
any integer cap lets a column look ``NOT NULL`` across the first N rows
while the file actually holds rare nulls past the window, which then
detonates ``COPY`` mid-stream (seen in production on a 2.5M-row file where
~6k MAFIDs were null past the 10k-row preview). If you're loading a file
so large that a full read won't fit in memory, set this to an integer cap
and accept that sampled specs can't be trusted for ``NOT NULL``."""

DEFAULT_CHUNK_ROWS = 2_000_000
"""Rows per chunk when streaming a SAS file into ``COPY``. Larger values mean
fewer COPY round-trips and lower per-row overhead but more peak memory per
chunk; smaller values are gentler on memory.

The chunk size can be overridden at runtime via the
``GENERIC_LOADER_CHUNK_ROWS`` environment variable (read inside
:func:`iter_sas_chunks`), so ``.env``-driven overrides work without code
changes. Explicit ``chunksize=`` kwargs still win over both."""


VALID_IF_EXISTS = ("fail", "replace", "append")

_PG_IDENT_MAX_LEN = 63
"""PostgreSQL maximum identifier length in bytes (characters for ASCII)."""


# ---------------------------------------------------------------------------
# Dataclasses
# ---------------------------------------------------------------------------


@dataclass
class LoaderConfig:
    filename: Path
    schemaname: str
    tablename: str
    if_exists: str = "fail"
    include: Optional[List[str]] = None
    exclude: Optional[List[str]] = None
    partition_by: List[str] = field(default_factory=list)
    max_partitions: int = 10_000
    indexes: List[str] = field(default_factory=list)


@dataclass
class ColumnSpec:
    name: str
    postgres_type: str
    nullable: bool
    sas_format: Optional[str] = None
    source_dtype: Optional[str] = None
    notes: List[str] = field(default_factory=list)
    sampled: bool = False
    """True when the type was inferred from a bounded preview rather than the
    full file. A sampled spec carries the usual sampling risks: a later chunk
    could contain a value that exceeds the inferred integer range, doesn't
    parse as the inferred type, or is null in a column the preview showed as
    non-null - all of which surface as mid-``COPY`` failures."""


# ---------------------------------------------------------------------------
# Custom exceptions
# ---------------------------------------------------------------------------


class TableExistsError(RuntimeError):
    """Raised when if_exists=fail and the target table already exists."""


class SchemaCompatibilityError(RuntimeError):
    """Raised when if_exists=append and the incoming schema is not
    compatible with the existing table."""


class ValidationError(RuntimeError):
    """Raised when --validate detects a mismatch against the manifest."""


# ---------------------------------------------------------------------------
# Connection
# ---------------------------------------------------------------------------


def connect(
    *,
    user: Optional[str] = None,
    password: Optional[str] = None,
) -> psycopg2.extensions.connection:
    """Open a psycopg2 connection using standard libpq env vars.

    Assumes `.env` has already been loaded (the CLI does this before calling).
    Orchestrators that wrap this module should either call ``load_dotenv()``
    themselves or ensure the env vars are set.

    ``user`` and ``password`` override the corresponding env vars when supplied
    (used by the ``--dbcreds`` CLI flag to accept interactive input).
    """
    conn = psycopg2.connect(
        host=os.environ.get("PGHOST"),
        port=os.environ.get("PGPORT"),
        user=user or os.environ.get("PGUSER"),
        password=password or os.environ.get("PGPASSWORD"),
        dbname=os.environ.get("PGDATABASE"),
    )
    return conn


# ---------------------------------------------------------------------------
# Config loading
# ---------------------------------------------------------------------------


def load_config(path: Path) -> LoaderConfig:
    """Parse and validate the YAML config at ``path``."""
    path = Path(path)
    with path.open("r", encoding="utf-8") as f:
        raw = yaml.safe_load(f)

    if not isinstance(raw, dict):
        raise ValueError(f"Config at {path} must be a YAML mapping at the top level.")

    missing = [k for k in ("filename", "schemaname", "tablename") if k not in raw]
    if missing:
        raise ValueError(f"Config {path} missing required keys: {', '.join(missing)}")

    filename = Path(raw["filename"])
    if not filename.is_absolute():
        filename = (path.parent / filename).resolve() if (path.parent / filename).exists() else Path(raw["filename"])

    schemaname = str(raw["schemaname"])
    tablename = str(raw["tablename"])

    if_exists = str(raw.get("if_exists", "fail")).lower()
    if if_exists not in VALID_IF_EXISTS:
        raise ValueError(
            f"Config {path}: if_exists={if_exists!r} is not one of {VALID_IF_EXISTS}"
        )

    include = raw.get("include")
    exclude = raw.get("exclude")
    if include is not None and exclude is not None:
        raise ValueError(
            f"Config {path}: 'include' and 'exclude' are mutually exclusive; set at most one."
        )
    if include is not None and not isinstance(include, list):
        raise ValueError(f"Config {path}: 'include' must be a list of column names.")
    if exclude is not None and not isinstance(exclude, list):
        raise ValueError(f"Config {path}: 'exclude' must be a list of column names.")

    # -- partition_by -------------------------------------------------------
    raw_pb = raw.get("partition_by")
    if raw_pb is None or (isinstance(raw_pb, list) and len(raw_pb) == 0):
        partition_by: List[str] = []
    elif isinstance(raw_pb, str):
        if not raw_pb.strip():
            raise ValueError(f"Config {path}: 'partition_by' string must be non-empty.")
        partition_by = [raw_pb.strip()]
    elif isinstance(raw_pb, list):
        partition_by = []
        for i, item in enumerate(raw_pb):
            if not isinstance(item, str) or not item.strip():
                raise ValueError(
                    f"Config {path}: 'partition_by[{i}]' must be a non-empty string."
                )
            partition_by.append(str(item).strip())
        if len(partition_by) != len(set(partition_by)):
            raise ValueError(
                f"Config {path}: 'partition_by' contains duplicate column names."
            )
    else:
        raise ValueError(
            f"Config {path}: 'partition_by' must be a string or list of strings."
        )

    # Validate partition_by vs include/exclude
    if partition_by:
        inc_list = [str(c) for c in include] if include is not None else None
        exc_list = [str(c) for c in exclude] if exclude is not None else None
        if inc_list is not None:
            missing_in_include = [c for c in partition_by if c not in inc_list]
            if missing_in_include:
                raise ValueError(
                    f"Config {path}: 'include' omits partition_by columns: "
                    f"{missing_in_include}"
                )
        if exc_list is not None:
            excluded_parts = [c for c in partition_by if c in exc_list]
            if excluded_parts:
                raise ValueError(
                    f"Config {path}: 'exclude' removes partition_by columns: "
                    f"{excluded_parts}"
                )

    # -- max_partitions -----------------------------------------------------
    raw_mp = raw.get("max_partitions", 10_000)
    try:
        max_partitions = int(raw_mp)
    except (TypeError, ValueError):
        raise ValueError(
            f"Config {path}: 'max_partitions' must be a positive integer, "
            f"got {raw_mp!r}"
        )
    if max_partitions <= 0:
        raise ValueError(
            f"Config {path}: 'max_partitions' must be a positive integer, "
            f"got {max_partitions}"
        )

    # -- indexes ------------------------------------------------------------
    raw_idx = raw.get("indexes")
    if raw_idx is None or (isinstance(raw_idx, list) and len(raw_idx) == 0):
        indexes: List[str] = []
    elif isinstance(raw_idx, str):
        if not raw_idx.strip():
            raise ValueError(f"Config {path}: 'indexes' string must be non-empty.")
        indexes = [raw_idx.strip()]
    elif isinstance(raw_idx, list):
        indexes = []
        for i, item in enumerate(raw_idx):
            if not isinstance(item, str) or not item.strip():
                raise ValueError(
                    f"Config {path}: 'indexes[{i}]' must be a non-empty string."
                )
            indexes.append(str(item).strip())
        if len(indexes) != len(set(indexes)):
            raise ValueError(
                f"Config {path}: 'indexes' contains duplicate column names."
            )
    else:
        raise ValueError(
            f"Config {path}: 'indexes' must be a string or list of strings."
        )

    # Validate indexes vs include/exclude
    if indexes:
        inc_list = [str(c) for c in include] if include is not None else None
        exc_list = [str(c) for c in exclude] if exclude is not None else None
        if exc_list is not None:
            excluded_idx = [c for c in indexes if c in exc_list]
            if excluded_idx:
                raise ValueError(
                    f"Config {path}: 'exclude' removes index columns: "
                    f"{excluded_idx}"
                )
        if inc_list is not None:
            missing_in_include = [c for c in indexes if c not in inc_list]
            if missing_in_include:
                raise ValueError(
                    f"Config {path}: 'include' omits index columns: "
                    f"{missing_in_include}"
                )

    return LoaderConfig(
        filename=filename,
        schemaname=schemaname,
        tablename=tablename,
        if_exists=if_exists,
        include=[str(c) for c in include] if include is not None else None,
        exclude=[str(c) for c in exclude] if exclude is not None else None,
        partition_by=partition_by,
        max_partitions=max_partitions,
        indexes=indexes,
    )


# ---------------------------------------------------------------------------
# Reader
# ---------------------------------------------------------------------------


def _sas_reader(path: Path) -> Tuple[Any, Dict[str, Any]]:
    """Return ``(pyreadstat_reader, extra_kwargs)`` for ``path``.

    Invariants (learned the hard way while building the sample generator):

    * ``.xpt`` / ``.xport`` - no encoding arg; pyreadstat is flaky about
      encoding on XPORT files it wrote itself.
    * ``.sas7bdat`` - explicit ``encoding="latin-1"`` per colleague guidance.
    """
    suffix = Path(path).suffix.lower()
    if suffix in (".xpt", ".xport"):
        return pyreadstat.read_xport, {}
    if suffix == ".sas7bdat":
        return pyreadstat.read_sas7bdat, {}
    raise ValueError(f"Unsupported SAS file extension: {suffix}")


def read_sas(path: Path) -> Tuple[pd.DataFrame, Any]:
    """Read an entire SAS file into memory. Only safe for small files.

    Kept for backward compatibility and tests; the CLI now uses
    :func:`read_sas_preview` + :func:`iter_sas_chunks` so it never materializes
    the whole frame at once.
    """
    reader, kwargs = _sas_reader(path)
    return reader(str(Path(path)), **kwargs)


def read_sas_preview(
    path: Path,
    *,
    rows: Optional[int] = None,
) -> Tuple[pd.DataFrame, Any]:
    """Read the first ``rows`` records from ``path`` plus its metadata.

    Defaults to ``TYPE_INFERENCE_SAMPLE_ROWS`` when ``rows`` is not given.
    Passing ``rows=None`` with ``TYPE_INFERENCE_SAMPLE_ROWS=None`` reads the
    whole file (pyreadstat treats ``row_limit=0`` as unlimited).
    """
    reader, kwargs = _sas_reader(path)
    effective = rows if rows is not None else TYPE_INFERENCE_SAMPLE_ROWS
    row_limit = int(effective) if effective else 0
    return reader(str(Path(path)), row_limit=row_limit, **kwargs)


def read_sas_metadata(path: Path) -> Any:
    """Read only the metadata (no rows) from a SAS file.

    Uses pyreadstat's ``metadataonly=True`` fast path: the reader decodes
    the file header (column names, formats, total row count, etc.) and
    returns without touching the data pages. Orders of magnitude faster
    than :func:`read_sas_preview` when all you need is
    ``meta.number_rows`` - typically a few ms per sas7bdat file, which
    makes it cheap to pre-scan a whole folder to populate a global
    progress bar.
    """
    reader, kwargs = _sas_reader(path)
    _, meta = reader(str(Path(path)), metadataonly=True, **kwargs)
    return meta


def iter_sas_chunks(
    path: Path,
    *,
    chunksize: Optional[int] = None,
):
    """Yield ``(df_chunk, meta)`` tuples for streaming loads.

    Thin wrapper over ``pyreadstat.read_file_in_chunks`` that picks the right
    underlying reader by extension and threads through our encoding defaults.

    When ``chunksize`` is ``None`` (the default), the effective value comes
    from the ``GENERIC_LOADER_CHUNK_ROWS`` environment variable if set and
    parseable, otherwise from :data:`DEFAULT_CHUNK_ROWS`. An explicit int
    always wins.
    """
    if chunksize is None:
        raw = os.environ.get("GENERIC_LOADER_CHUNK_ROWS")
        if raw is not None:
            try:
                chunksize = int(raw)
            except ValueError:
                chunksize = DEFAULT_CHUNK_ROWS
        else:
            chunksize = DEFAULT_CHUNK_ROWS
    reader, kwargs = _sas_reader(path)
    yield from pyreadstat.read_file_in_chunks(
        reader, str(Path(path)), chunksize=chunksize, **kwargs
    )


# ---------------------------------------------------------------------------
# Column filtering
# ---------------------------------------------------------------------------


def apply_column_filter(
    df: pd.DataFrame,
    include: Optional[List[str]],
    exclude: Optional[List[str]],
) -> pd.DataFrame:
    """Restrict ``df`` to the requested columns. Names missing from the frame
    raise a clear error rather than silently dropping.

    Returns the input frame (or a column-sliced view / drop result) without
    an extra ``.copy()`` — downstream (:func:`_prepare_for_copy`) reads the
    frame into a freshly built output and never mutates its input, so the
    copies were pure overhead on every streamed chunk.
    """
    if include is not None and exclude is not None:
        raise ValueError("include and exclude are mutually exclusive.")

    if include is not None:
        missing = [c for c in include if c not in df.columns]
        if missing:
            raise ValueError(f"include references unknown columns: {missing}")
        return df.loc[:, list(include)]

    if exclude is not None:
        missing = [c for c in exclude if c not in df.columns]
        if missing:
            raise ValueError(f"exclude references unknown columns: {missing}")
        return df.drop(columns=list(exclude))

    return df


# ---------------------------------------------------------------------------
# Type inference
# ---------------------------------------------------------------------------


_DATE_FORMAT_PREFIXES = ("DATE", "YYMMDD", "MMDDYY", "DDMMYY", "JULIAN")


def _format_driven_type(sas_format: Optional[str]) -> Optional[str]:
    """Return a Postgres type inferred from the SAS format string, or None
    if the format doesn't pin it down."""
    if not sas_format:
        return None
    fmt = sas_format.upper().lstrip()
    # DATETIME must be checked before DATE since "DATETIME20." starts with "DATE".
    if fmt.startswith("DATETIME"):
        return "TIMESTAMP"
    if fmt.startswith("TIME"):
        return "TIME"
    for prefix in _DATE_FORMAT_PREFIXES:
        if fmt.startswith(prefix):
            return "DATE"
    return None


def _all_null(series: pd.Series) -> bool:
    if pd.api.types.is_object_dtype(series):
        return bool(series.map(lambda v: v is None or (isinstance(v, str) and v == "") or (isinstance(v, float) and pd.isna(v))).all())
    return bool(series.isna().all())


def _char_missing_mask(series: pd.Series) -> pd.Series:
    return series.map(lambda v: v is None or (isinstance(v, float) and pd.isna(v)) or (isinstance(v, str) and v == ""))


def _is_nullable(series: pd.Series) -> bool:
    """True if the column has at least one missing value."""
    if pd.api.types.is_object_dtype(series):
        return bool(_char_missing_mask(series).any())
    return bool(series.isna().any())


def _numeric_int_target(series: pd.Series) -> Optional[str]:
    """Given a numeric (float64) series, if every non-null value is a whole
    number, return INTEGER or BIGINT depending on range; else None."""
    nonnull = series.dropna()
    if nonnull.empty:
        return None
    # Whole-number test. Guard against inf.
    try:
        whole = ((nonnull % 1) == 0).all()
    except TypeError:
        return None
    if not whole:
        return None
    lo, hi = NUMERIC_INT_RANGE
    vmin = nonnull.min()
    vmax = nonnull.max()
    if lo <= vmin and vmax <= hi:
        return "INTEGER"
    return "BIGINT"


def _object_is_dates(series: pd.Series) -> Tuple[bool, bool]:
    """Return (all-date-like, any-datetime). If every non-null value is a
    ``datetime.date`` / ``datetime.datetime`` / ``pd.Timestamp``, return True
    plus whether at least one carries a time component."""
    nonnull = series.dropna()
    if nonnull.empty:
        return False, False
    any_datetime = False
    for v in nonnull:
        if isinstance(v, dt.datetime) or isinstance(v, pd.Timestamp):
            any_datetime = True
            continue
        if isinstance(v, dt.date):
            continue
        return False, False
    return True, any_datetime


def _try_int_coerce(values: List[str]) -> Optional[str]:
    """If every value parses as an int, return INTEGER/BIGINT, else None."""
    ints: List[int] = []
    for v in values:
        s = v.strip()
        try:
            ints.append(int(s))
        except ValueError:
            return None
    if not ints:
        return None
    lo, hi = NUMERIC_INT_RANGE
    if all(lo <= i <= hi for i in ints):
        return "INTEGER"
    return "BIGINT"


def _try_float_coerce(values: List[str]) -> bool:
    for v in values:
        try:
            float(v)
        except ValueError:
            return False
    return True


def _try_date_coerce(values: List[str]) -> bool:
    for v in values:
        try:
            dt.date.fromisoformat(v)
        except (ValueError, TypeError):
            return False
    return True


def _try_datetime_coerce(values: List[str]) -> bool:
    for v in values:
        try:
            dt.datetime.fromisoformat(v)
        except (ValueError, TypeError):
            return False
    return True


def _infer_char_type(series: pd.Series) -> str:
    """Object/string column inference. Returns a Postgres type string."""
    mask = _char_missing_mask(series)
    nonempty = [str(v) for v in series[~mask].tolist()]
    if not COERCE_CHAR_COLUMNS or len(nonempty) < CHAR_INFERENCE_MIN_VALUES:
        return "TEXT"

    int_guess = _try_int_coerce(nonempty)
    if int_guess is not None:
        return int_guess
    if _try_float_coerce(nonempty):
        return "DOUBLE PRECISION"
    if _try_date_coerce(nonempty):
        return "DATE"
    if _try_datetime_coerce(nonempty):
        return "TIMESTAMP"
    return "TEXT"


def infer_schema(
    df: pd.DataFrame,
    meta: Any,
    *,
    coerce_chars: bool = COERCE_CHAR_COLUMNS,
    total_rows: Optional[int] = None,
) -> Dict[str, ColumnSpec]:
    """Infer a Postgres column spec for each column in ``df``.

    ``meta`` is the pyreadstat metadata object; we read
    ``meta.original_variable_types`` (a dict keyed by column name) for
    format-driven date/time/timestamp inference.

    The ``coerce_chars`` kwarg lets callers override the module-level
    ``COERCE_CHAR_COLUMNS`` without mutating global state. Internally the
    char-inference helpers still read the constant - a full override would
    thread the flag through, but the one-knob story here is intentional.

    ``total_rows`` lets callers who already sampled the frame (e.g. via
    :func:`read_sas_preview`) report the real file size in the per-column
    "inferred from first N of M rows" note. Falls back to ``len(df)``.
    """
    original_formats: Dict[str, str] = dict(getattr(meta, "original_variable_types", {}) or {})

    # When ``TYPE_INFERENCE_SAMPLE_ROWS`` is an integer cap, row-walking type
    # probes run on the head slice for speed; nullability and the all-null
    # check still walk every row of ``df``. That's only honest when the
    # caller handed us the full file - with the default cap of ``None`` the
    # CLI does exactly that. Callers who pass a partial preview and a tight
    # integer cap accept that ``NOT NULL`` can be wrong for rare-null columns.
    df_rows = len(df)
    effective_total = total_rows if total_rows is not None else df_rows
    if TYPE_INFERENCE_SAMPLE_ROWS is not None and df_rows > TYPE_INFERENCE_SAMPLE_ROWS:
        sample_df = df.head(TYPE_INFERENCE_SAMPLE_ROWS)
        sample_size = TYPE_INFERENCE_SAMPLE_ROWS
    else:
        sample_df = df
        sample_size = df_rows
    sampled = sample_size < effective_total

    # Temporarily flip the module-level flag if the caller asked us to.
    global COERCE_CHAR_COLUMNS
    saved = COERCE_CHAR_COLUMNS
    COERCE_CHAR_COLUMNS = coerce_chars
    try:
        out: Dict[str, ColumnSpec] = {}
        for col in df.columns:
            series = df[col]
            sample_series = sample_df[col]
            sas_format = original_formats.get(col)
            notes: List[str] = []

            pg_type = _format_driven_type(sas_format)

            if pg_type is None:
                if _all_null(series):
                    pg_type = "TEXT"
                    notes.append("all-null column; defaulting to TEXT")
                elif pd.api.types.is_datetime64_any_dtype(series):
                    pg_type = "TIMESTAMP"
                elif pd.api.types.is_object_dtype(series):
                    is_dates, any_dt = _object_is_dates(sample_series)
                    if is_dates:
                        pg_type = "TIMESTAMP" if any_dt else "DATE"
                    else:
                        pg_type = _infer_char_type(sample_series)
                elif pd.api.types.is_numeric_dtype(series):
                    int_target = _numeric_int_target(sample_series)
                    if int_target is not None:
                        pg_type = int_target
                    else:
                        pg_type = "DOUBLE PRECISION"
                else:
                    pg_type = "TEXT"
                    notes.append(f"unhandled dtype {series.dtype}; defaulting to TEXT")

                if sampled:
                    notes.append(
                        f"type inferred from first {sample_size:,} of "
                        f"{effective_total:,} rows"
                    )

            nullable = _is_nullable(series)

            out[col] = ColumnSpec(
                name=col,
                postgres_type=pg_type,
                nullable=nullable,
                sas_format=sas_format,
                source_dtype=str(series.dtype),
                notes=notes,
                sampled=sampled,
            )
        return out
    finally:
        COERCE_CHAR_COLUMNS = saved


# ---------------------------------------------------------------------------
# Table management
# ---------------------------------------------------------------------------


def _quote_ident(ident: str) -> str:
    """Quote a Postgres identifier. psycopg2 doesn't expose this directly
    until 2.8+ with sql.Identifier; we do it by hand to stay driver-simple."""
    return '"' + ident.replace('"', '""') + '"'


def _qualified(schema: str, table: str) -> str:
    return f"{_quote_ident(schema)}.{_quote_ident(table)}"


def _table_exists(conn, schema: str, table: str) -> bool:
    with conn.cursor() as cur:
        cur.execute(
            "SELECT 1 FROM information_schema.tables "
            "WHERE table_schema = %s AND table_name = %s",
            (schema, table),
        )
        return cur.fetchone() is not None


def render_create_table(
    schema: str,
    table: str,
    columns: Dict[str, ColumnSpec],
    *,
    partition_by: Optional[List[str]] = None,
) -> str:
    """Render a ``CREATE TABLE`` statement.

    When ``partition_by`` is provided and non-empty, appends a
    ``PARTITION BY LIST ("first_field")`` clause to the statement.
    """
    lines = []
    for spec in columns.values():
        null_clause = "" if spec.nullable else " NOT NULL"
        lines.append(f"    {_quote_ident(spec.name)} {spec.postgres_type}{null_clause}")
    body = ",\n".join(lines)
    suffix = ""
    if partition_by:
        suffix = f"\nPARTITION BY LIST ({_quote_ident(partition_by[0])})"
    return f"CREATE TABLE {_qualified(schema, table)} (\n{body}\n){suffix};"


def _create_table_sql(
    conn,
    schema: str,
    table: str,
    columns: Dict[str, ColumnSpec],
    *,
    partition_by: Optional[List[str]] = None,
) -> None:
    """Execute a ``CREATE TABLE`` statement, optionally with partitioning."""
    sql = render_create_table(schema, table, columns, partition_by=partition_by)
    with conn.cursor() as cur:
        cur.execute(sql)


def _drop_table(conn, schema: str, table: str, *, cascade: bool = False) -> None:
    """Drop a table, optionally with CASCADE for partitioned tables."""
    tail = " CASCADE" if cascade else ""
    with conn.cursor() as cur:
        cur.execute(f"DROP TABLE {_qualified(schema, table)}{tail}")


# Normalization table: map both loader-emitted and Postgres-reported type
# strings to a single canonical family name. Ignore length/precision
# modifiers like VARCHAR(n) and NUMERIC(p,s).
_TYPE_NORMALIZATION: Dict[str, str] = {
    "INTEGER": "integer",
    "INT": "integer",
    "INT4": "integer",
    "BIGINT": "bigint",
    "INT8": "bigint",
    "SMALLINT": "smallint",
    "INT2": "smallint",
    "DOUBLE PRECISION": "double precision",
    "FLOAT8": "double precision",
    "REAL": "real",
    "FLOAT4": "real",
    "NUMERIC": "numeric",
    "DECIMAL": "numeric",
    "TEXT": "text",
    "VARCHAR": "character varying",
    "CHARACTER VARYING": "character varying",
    "CHAR": "character",
    "CHARACTER": "character",
    "BPCHAR": "character",
    "BOOLEAN": "boolean",
    "BOOL": "boolean",
    "DATE": "date",
    "TIMESTAMP": "timestamp without time zone",
    "TIMESTAMP WITHOUT TIME ZONE": "timestamp without time zone",
    "TIMESTAMPTZ": "timestamp with time zone",
    "TIMESTAMP WITH TIME ZONE": "timestamp with time zone",
    "TIME": "time without time zone",
    "TIME WITHOUT TIME ZONE": "time without time zone",
    "TIMETZ": "time with time zone",
    "TIME WITH TIME ZONE": "time with time zone",
}


def _normalize_type(pg_type: str) -> str:
    """Strip length/precision modifiers and map to canonical family."""
    stripped = pg_type.strip().upper()
    # Remove trailing (n) / (p,s) before the space-separated tail.
    # Examples: "VARCHAR(10)" -> "VARCHAR"; "TIMESTAMP(6) WITHOUT TIME ZONE" -> "TIMESTAMP WITHOUT TIME ZONE"
    stripped = re.sub(r"\(\s*\d+\s*(?:,\s*\d+\s*)?\)", "", stripped).strip()
    # Collapse doubled whitespace after paren removal.
    stripped = re.sub(r"\s+", " ", stripped)
    return _TYPE_NORMALIZATION.get(stripped, stripped.lower())


# Widening pairs: (inferred_from_source, existing_in_target). When the
# incoming spec is narrower than the target we accept it - the value is
# guaranteed to fit, and ``_prepare_for_copy`` already emits ``COPY``
# payloads that Postgres silently promotes to the wider column type. The
# INVERSE direction stays a hard failure: a BIGINT value does not fit in
# an INTEGER column, so we must not let a cluster whose first file had
# only small ints accept a later file with a value past int32. Comes up
# most often on cluster loads where file 1 pushed the target to BIGINT
# (a single value > 2_147_483_647) and file N happens to sit entirely
# within int32 range - strict equality would reject file N even though
# the copy is trivially safe.
_WIDENING_COMPATIBLE: set = {
    ("smallint", "integer"),
    ("smallint", "bigint"),
    ("integer", "bigint"),
    ("real", "double precision"),
    # INTEGER / BIGINT into DOUBLE PRECISION is lossless for int32 and
    # exact up to 2**53 for int64, which covers every value pandas could
    # have carried through as Int64 without wrapping anyway.
    ("integer", "double precision"),
    ("bigint", "double precision"),
}


def _assert_schema_compatible(
    conn, schema: str, table: str, columns: Dict[str, ColumnSpec]
) -> None:
    """Pre-flight check for if_exists=append. See plan section on option B."""
    with conn.cursor() as cur:
        cur.execute(
            "SELECT column_name, data_type, is_nullable "
            "FROM information_schema.columns "
            "WHERE table_schema = %s AND table_name = %s",
            (schema, table),
        )
        existing = {row[0]: (row[1], row[2]) for row in cur.fetchall()}

    mismatches: List[str] = []
    warnings: List[str] = []

    for name, spec in columns.items():
        if name not in existing:
            mismatches.append(
                f"column {name!r} not present in target {schema}.{table}"
            )
            continue
        target_type, target_nullable = existing[name]
        inferred_norm = _normalize_type(spec.postgres_type)
        target_norm = _normalize_type(target_type)
        if inferred_norm != target_norm:
            if (inferred_norm, target_norm) in _WIDENING_COMPATIBLE:
                # Narrower inferred type fits inside the wider target.
                # Accept silently-but-noisily so the operator knows the
                # file came in with a smaller range than the cluster's
                # target was sized for.
                warnings.append(
                    f"column {name!r}: inferred {spec.postgres_type} "
                    f"(narrower than target {target_type}); accepting - "
                    f"values fit in the wider target type"
                )
            else:
                mismatches.append(
                    f"column {name!r}: inferred {spec.postgres_type} "
                    f"(normalized {inferred_norm!r}) but target is {target_type} "
                    f"(normalized {target_norm!r})"
                )
        target_is_notnull = (target_nullable == "NO")
        if spec.nullable and target_is_notnull:
            warnings.append(
                f"column {name!r}: incoming allows NULLs but target is NOT NULL; "
                "COPY will fail if any NULLs appear"
            )

    for w in warnings:
        print(f"[warn] {w}", file=sys.stderr)

    if mismatches:
        raise SchemaCompatibilityError(
            "append-mode schema compatibility check failed:\n  - "
            + "\n  - ".join(mismatches)
        )


def assert_schema_compatible(
    conn,
    schema_name: str,
    table_name: str,
    columns: Dict[str, ColumnSpec],
) -> None:
    """Public wrapper around :func:`_assert_schema_compatible`.

    Intended for orchestrators (e.g. the folder loader) that append multiple
    files into one table and need to re-run the same compatibility check
    that ``if_exists=append`` performs internally. Raises
    :class:`SchemaCompatibilityError` on mismatch.
    """
    _assert_schema_compatible(conn, schema_name, table_name, columns)


def create_table(
    conn,
    schema_name: str,
    table_name: str,
    columns: Dict[str, ColumnSpec],
    if_exists: str,
    *,
    partition_by: Optional[List[str]] = None,
    partition_values: Optional[dict] = None,
    max_partitions: int = 10_000,
) -> None:
    """Create (or verify) the target table according to ``if_exists``.

    When ``partition_by`` is provided and non-empty, the parent table is
    created with ``PARTITION BY LIST`` and all child partition DDL from
    :func:`render_partition_ddl` is executed immediately after.

    For ``replace`` mode the existing table is dropped with ``CASCADE`` so
    all child partitions are removed automatically.

    For ``append`` mode partition creation is skipped entirely — the
    partitions are assumed to already exist from the original creation.
    """
    if if_exists not in VALID_IF_EXISTS:
        raise ValueError(f"if_exists must be one of {VALID_IF_EXISTS}, got {if_exists!r}")

    is_partitioned = bool(partition_by)

    exists = _table_exists(conn, schema_name, table_name)
    if exists:
        if if_exists == "fail":
            raise TableExistsError(
                f"Table {schema_name}.{table_name} already exists and if_exists=fail"
            )
        if if_exists == "replace":
            _drop_table(conn, schema_name, table_name, cascade=is_partitioned)
            _create_table_sql(
                conn, schema_name, table_name, columns,
                partition_by=partition_by,
            )
            if is_partitioned and partition_values is not None:
                ddl_stmts = render_partition_ddl(
                    schema_name, table_name, partition_by, partition_values,
                    columns, max_partitions=max_partitions,
                )
                with conn.cursor() as cur:
                    for stmt in ddl_stmts:
                        cur.execute(stmt)
            return
        if if_exists == "append":
            _assert_schema_compatible(conn, schema_name, table_name, columns)
            return
    else:
        _create_table_sql(
            conn, schema_name, table_name, columns,
            partition_by=partition_by,
        )
        if is_partitioned and partition_values is not None:
            ddl_stmts = render_partition_ddl(
                schema_name, table_name, partition_by, partition_values,
                columns, max_partitions=max_partitions,
            )
            with conn.cursor() as cur:
                for stmt in ddl_stmts:
                    cur.execute(stmt)


# ---------------------------------------------------------------------------
# Partition support
# ---------------------------------------------------------------------------


def _sanitize_partition_value(value: Any, parent_table: str = "") -> str:
    """Convert a partition value into a safe, deterministic table-name suffix.

    Rules:
    - Convert to string, lowercase
    - Replace non-alphanumeric runs with ``_``
    - Collapse consecutive underscores, strip leading/trailing ``_``
    - None/NaN → ``null``; empty string → ``empty``
    - Truncate to fit within PostgreSQL's 63-character identifier limit
      accounting for ``parent_table`` + ``_`` separator
    """
    if value is None or (isinstance(value, float) and (pd.isna(value) or math.isnan(value))):
        token = "null"
    elif isinstance(value, dt.date) or isinstance(value, dt.datetime):
        token = value.isoformat()
    elif isinstance(value, dt.time):
        token = value.isoformat()
    else:
        token = str(value)

    token = token.lower()
    token = re.sub(r"[^a-z0-9]+", "_", token)
    token = re.sub(r"_+", "_", token)
    token = token.strip("_")

    if not token:
        if value is None or (isinstance(value, float) and pd.isna(value)):
            token = "null"
        elif isinstance(value, str) and value == "":
            token = "empty"
        else:
            token = "value"

    # Truncate to keep total table name within PG's 63-char limit.
    if parent_table:
        # Reserve room for parent + underscore separator.
        max_token_len = _PG_IDENT_MAX_LEN - len(parent_table) - 1
        if max_token_len < 1:
            raise ValueError(
                f"Parent table name {parent_table!r} is too long "
                f"({len(parent_table)} chars) to create child partitions."
            )
        if len(token) > max_token_len:
            token = token[:max_token_len].rstrip("_")

    return token


def _render_partition_value_literal(value: Any, pg_type: str) -> str:
    """Render a Python value as a SQL literal for ``FOR VALUES IN (...)``.

    - None/NaN → ``NULL``
    - Strings → single-quoted with ``'`` escaped to ``''``
    - Numbers → plain numeric literal
    - Booleans → ``TRUE`` / ``FALSE``
    - Dates → ``DATE 'YYYY-MM-DD'``
    - Timestamps → ``TIMESTAMP 'YYYY-MM-DD HH:MM:SS'``
    - Times → ``TIME 'HH:MM:SS'``
    """
    if value is None or (isinstance(value, float) and pd.isna(value)):
        return "NULL"

    pg_upper = pg_type.upper()

    if pg_upper in ("BOOLEAN", "BOOL"):
        return "TRUE" if value else "FALSE"

    if pg_upper in ("INTEGER", "BIGINT", "SMALLINT", "INT", "INT4", "INT8", "INT2"):
        return str(int(value))

    if pg_upper in ("DOUBLE PRECISION", "REAL", "NUMERIC", "DECIMAL",
                     "FLOAT4", "FLOAT8"):
        return str(value)

    if pg_upper == "DATE":
        if isinstance(value, (dt.date, dt.datetime)):
            return f"DATE '{value.isoformat()}'"
        return f"DATE '{value}'"

    if pg_upper in ("TIMESTAMP", "TIMESTAMP WITHOUT TIME ZONE",
                     "TIMESTAMP WITH TIME ZONE", "TIMESTAMPTZ"):
        if isinstance(value, (dt.datetime, pd.Timestamp)):
            return f"TIMESTAMP '{value.isoformat()}'"
        if isinstance(value, dt.date):
            return f"TIMESTAMP '{dt.datetime(value.year, value.month, value.day).isoformat()}'"
        return f"TIMESTAMP '{value}'"

    if pg_upper in ("TIME", "TIME WITHOUT TIME ZONE",
                     "TIME WITH TIME ZONE", "TIMETZ"):
        if isinstance(value, dt.time):
            return f"TIME '{value.isoformat()}'"
        return f"TIME '{value}'"

    # Default: treat as text — single-quote with escaping.
    escaped = str(value).replace("'", "''")
    return f"'{escaped}'"


def _normalize_partition_value(value: Any, pg_type: str) -> Any:
    """Normalize a raw partition value to its Python-native form.

    Applies the same semantic normalization that :func:`_prepare_for_copy`
    uses, so partition discovery deduplicates on the routed value rather
    than the raw source representation.
    """
    # Handle pandas null types
    if value is None:
        return None
    if isinstance(value, float) and (pd.isna(value) or math.isnan(value)):
        return None
    try:
        if pd.isna(value):
            return None
    except (TypeError, ValueError):
        pass

    pg_upper = pg_type.upper()

    if pg_upper in ("INTEGER", "BIGINT", "SMALLINT", "INT", "INT4", "INT8", "INT2"):
        if isinstance(value, str):
            value = value.strip()
            if value == "":
                return None
        try:
            return int(float(value))
        except (TypeError, ValueError):
            return None

    if pg_upper in ("DOUBLE PRECISION", "REAL", "NUMERIC", "DECIMAL",
                     "FLOAT4", "FLOAT8"):
        if isinstance(value, str):
            value = value.strip()
            if value == "":
                return None
        try:
            result = float(value)
            return None if math.isnan(result) else result
        except (TypeError, ValueError):
            return None

    if pg_upper == "DATE":
        if isinstance(value, dt.datetime):
            return value.date()
        if isinstance(value, dt.date):
            return value
        if isinstance(value, str):
            if value.strip() == "":
                return None
            try:
                return dt.date.fromisoformat(value.strip())
            except (ValueError, TypeError):
                return None
        return None

    if pg_upper in ("TIMESTAMP", "TIMESTAMP WITHOUT TIME ZONE",
                     "TIMESTAMP WITH TIME ZONE", "TIMESTAMPTZ"):
        if isinstance(value, dt.datetime):
            return value
        if isinstance(value, pd.Timestamp):
            return value.to_pydatetime() if not pd.isna(value) else None
        if isinstance(value, dt.date):
            return dt.datetime(value.year, value.month, value.day)
        if isinstance(value, str):
            if value.strip() == "":
                return None
            try:
                return dt.datetime.fromisoformat(value.strip())
            except (ValueError, TypeError):
                return None
        return None

    if pg_upper in ("TIME", "TIME WITHOUT TIME ZONE",
                     "TIME WITH TIME ZONE", "TIMETZ"):
        return _seconds_to_time(value)

    if pg_upper in ("BOOLEAN", "BOOL"):
        if isinstance(value, bool):
            return value
        if isinstance(value, (int, float)):
            return bool(value)
        if isinstance(value, str):
            return value.strip().lower() in ("true", "1", "t", "yes")
        return None

    # Text-like types: None, pandas nulls, and '' all become None
    # because copy_dataframes() sends empty strings with NULL ''.
    if pg_upper in ("TEXT", "VARCHAR", "CHARACTER VARYING", "CHAR", "CHARACTER", "BPCHAR"):
        if isinstance(value, str):
            if value == "":
                return None
            return value
        return str(value)

    # Fallback: return as-is converted to native Python type
    if hasattr(value, "item"):
        return value.item()
    return value


def discover_partition_values(
    df: pd.DataFrame,
    partition_by: list[str],
    columns: Optional[Dict[str, ColumnSpec]] = None,
) -> dict:
    """Build a nested structure of unique partition values from a DataFrame.

    For ``partition_by = ['state', 'zip']`` returns::

        {
            'MO': {'63101': {}, '63102': {}},
            'IL': {'62001': {}, '62002': {}}
        }

    When ``columns`` is provided, values are normalized through
    :func:`_normalize_partition_value` to match the routed values Postgres
    will see during ``COPY``.

    None/NaN values are included as a distinct partition value (``None`` key).
    Values are converted to Python native types (not numpy types).
    """
    if not partition_by:
        return {}

    def _to_native(val: Any) -> Any:
        """Convert numpy scalars to Python native types."""
        if val is None:
            return None
        if isinstance(val, float) and pd.isna(val):
            return None
        if hasattr(val, "item"):
            return val.item()
        return val

    def _build_level(sub_df: pd.DataFrame, fields: list[str]) -> dict:
        if not fields or sub_df.empty:
            return {}

        field = fields[0]
        remaining = fields[1:]
        result: dict = {}

        # Get unique values, handling NaN
        unique_vals = sub_df[field].unique()

        for raw_val in unique_vals:
            val = _to_native(raw_val)

            # Normalize if column spec is available
            if columns and field in columns:
                val = _normalize_partition_value(val, columns[field].postgres_type)

            if remaining:
                # Filter rows matching this value
                if val is None:
                    mask = sub_df[field].isna() | sub_df[field].map(
                        lambda v: v is None or (isinstance(v, float) and pd.isna(v))
                        or (isinstance(v, str) and v == ""
                            and columns and field in columns
                            and columns[field].postgres_type.upper() in (
                                "TEXT", "VARCHAR", "CHARACTER VARYING",
                                "CHAR", "CHARACTER", "BPCHAR"))
                    )
                else:
                    mask = sub_df[field].map(lambda v, target=val: _matches(v, target, field))
                child_df = sub_df[mask]
                result[val] = _build_level(child_df, remaining)
            else:
                result[val] = {}

        return result

    def _matches(raw_val: Any, target: Any, field_name: str) -> bool:
        """Check if a raw value normalizes to the target."""
        native = _to_native(raw_val)
        if columns and field_name in columns:
            native = _normalize_partition_value(native, columns[field_name].postgres_type)
        if target is None:
            return native is None
        return native == target

    return _build_level(df, list(partition_by))


def discover_partition_values_chunked(
    chunk_iter: Iterable[pd.DataFrame],
    partition_by: list[str],
    columns: Optional[Dict[str, ColumnSpec]] = None,
) -> dict:
    """Discover partition values across an iterable of DataFrame chunks.

    Scans the entire file chunk-by-chunk, collecting unique partition
    column values and merging them into a single nested partition tree.
    This avoids materializing the full file in memory.
    """
    if not partition_by:
        return {}

    merged: dict = {}

    for chunk_df in chunk_iter:
        if chunk_df.empty:
            continue
        # Only keep partition columns to minimize memory
        part_cols = [c for c in partition_by if c in chunk_df.columns]
        if len(part_cols) != len(partition_by):
            missing = [c for c in partition_by if c not in chunk_df.columns]
            raise ValueError(
                f"Partition columns not found in data: {missing}"
            )
        sub_df = chunk_df[part_cols]
        chunk_tree = discover_partition_values(sub_df, partition_by, columns)
        _merge_partition_trees(merged, chunk_tree)

    return merged


def _merge_partition_trees(target: dict, source: dict) -> None:
    """Merge ``source`` partition tree into ``target`` in place.

    Both trees are nested dicts where keys are partition values and values
    are either empty dicts (leaf) or nested dicts (intermediate levels).
    """
    for key, subtree in source.items():
        if key not in target:
            target[key] = subtree
        else:
            # Merge children recursively
            if subtree and target[key]:
                _merge_partition_trees(target[key], subtree)
            elif subtree:
                target[key] = subtree


def _count_partitions(tree: dict) -> int:
    """Count total partition tables in a nested partition tree."""
    count = 0
    for _key, children in tree.items():
        count += 1
        if children:
            count += _count_partitions(children)
    return count


def render_partition_ddl(
    schema: str,
    parent_table: str,
    partition_by: list[str],
    partition_values: dict,
    column_specs: Dict[str, ColumnSpec],
    *,
    max_partitions: int = 10_000,
) -> list[str]:
    """Generate all child partition DDL statements for the partition tree.

    Returns a list of SQL strings to execute in order (depth-first).
    The parent ``CREATE TABLE`` is NOT included — it is rendered separately
    by :func:`render_create_table`.

    Logs a warning if the total partition count exceeds ``max_partitions``,
    but continues.
    """
    if not partition_by or not partition_values:
        return []

    total = _count_partitions(partition_values)
    if total > max_partitions:
        logger.warning(
            "Partition count (%d) exceeds threshold (%d). "
            "This may impact database performance.",
            total, max_partitions,
        )
        print(
            f"[warn] partition plan for {schema}.{parent_table} will create "
            f"{total:,} partition tables, exceeding max_partitions={max_partitions:,}",
            file=sys.stderr,
        )

    # Track used child names at each parent level to detect collisions
    statements: list[str] = []
    _render_partition_ddl_recursive(
        schema, parent_table, partition_by, partition_values,
        column_specs, 0, statements,
    )
    return statements


def _render_partition_ddl_recursive(
    schema: str,
    parent_table: str,
    partition_by: list[str],
    values: dict,
    column_specs: Dict[str, ColumnSpec],
    depth: int,
    statements: list[str],
) -> None:
    """Recursively generate partition DDL statements (depth-first)."""
    field_name = partition_by[depth]
    next_field = partition_by[depth + 1] if depth + 1 < len(partition_by) else None
    field_spec = column_specs.get(field_name)
    pg_type = field_spec.postgres_type if field_spec else "TEXT"

    # Track names used at this level under this parent to handle collisions
    used_names: Dict[str, Any] = {}

    # Sort values deterministically: None first, then by string representation
    def _sort_key(val: Any) -> Tuple[int, str]:
        if val is None:
            return (0, "")
        return (1, str(val))

    sorted_values = sorted(values.keys(), key=_sort_key)

    for val in sorted_values:
        children = values[val]
        token = _sanitize_partition_value(val, parent_table)
        child_name = f"{parent_table}_{token}"

        # Handle collisions
        if child_name in used_names and used_names[child_name] is not val:
            # Append a short hash of the value to disambiguate
            val_hash = hashlib.sha256(repr(val).encode()).hexdigest()[:8]
            # Re-truncate token to make room for _hash
            max_token_len = _PG_IDENT_MAX_LEN - len(parent_table) - 1 - 9  # _hash8
            if max_token_len < 1:
                max_token_len = 1
            truncated_token = token[:max_token_len].rstrip("_")
            child_name = f"{parent_table}_{truncated_token}_{val_hash}"

        # Final length check
        if len(child_name) > _PG_IDENT_MAX_LEN:
            child_name = child_name[:_PG_IDENT_MAX_LEN]

        used_names[child_name] = val

        literal = _render_partition_value_literal(val, pg_type)

        if next_field is not None:
            # Intermediate partition: itself partitioned by the next field
            stmt = (
                f"CREATE TABLE {_qualified(schema, child_name)} "
                f"PARTITION OF {_qualified(schema, parent_table)} "
                f"FOR VALUES IN ({literal}) "
                f"PARTITION BY LIST ({_quote_ident(next_field)});"
            )
            statements.append(stmt)
            # Recurse into children
            if children:
                _render_partition_ddl_recursive(
                    schema, child_name, partition_by, children,
                    column_specs, depth + 1, statements,
                )
        else:
            # Leaf partition
            stmt = (
                f"CREATE TABLE {_qualified(schema, child_name)} "
                f"PARTITION OF {_qualified(schema, parent_table)} "
                f"FOR VALUES IN ({literal});"
            )
            statements.append(stmt)


# ---------------------------------------------------------------------------
# Index support
# ---------------------------------------------------------------------------


def render_create_indexes(
    schema: str,
    tablename: str,
    indexes: List[str],
) -> List[str]:
    """Generate ``CREATE INDEX IF NOT EXISTS`` DDL for each column in *indexes*.

    Each index is a simple B-tree index on a single column.  The index name
    follows the pattern ``ix_{tablename}_{column}`` (raw, unsanitized names
    wrapped with :func:`_quote_ident`).  The table reference is fully
    qualified as ``schema.tablename``.

    If the generated index name exceeds PostgreSQL's 63-character identifier
    limit, it is truncated and a short hash suffix is appended to preserve
    uniqueness (similar to partition name truncation).

    Returns a list of SQL strings, one per index.
    """
    stmts: List[str] = []
    for col in indexes:
        idx_name = f"ix_{tablename}_{col}"
        if len(idx_name) > _PG_IDENT_MAX_LEN:
            # Truncate and append an 8-char hash for uniqueness.
            name_hash = hashlib.sha256(idx_name.encode()).hexdigest()[:8]
            # 9 = 1 underscore + 8 hash chars
            truncated = idx_name[: _PG_IDENT_MAX_LEN - 9].rstrip("_")
            idx_name = f"{truncated}_{name_hash}"
        stmt = (
            f"CREATE INDEX IF NOT EXISTS {_quote_ident(idx_name)} "
            f"ON {_qualified(schema, tablename)} ({_quote_ident(col)});"
        )
        stmts.append(stmt)
    return stmts


def create_indexes(
    conn,
    schema: str,
    tablename: str,
    indexes: List[str],
) -> None:
    """Execute ``CREATE INDEX IF NOT EXISTS`` for each column in *indexes*.

    Calls :func:`render_create_indexes` to obtain the DDL, executes each
    statement, commits immediately after each successful creation, and logs
    progress to stderr.  If an individual index creation fails (e.g. a name
    collision unrelated to ``IF NOT EXISTS``), the transaction is rolled back
    (affecting only the failed statement) and the remaining indexes are still
    attempted.
    """
    stmts = render_create_indexes(schema, tablename, indexes)
    with conn.cursor() as cur:
        for stmt, col in zip(stmts, indexes):
            try:
                cur.execute(stmt)
                conn.commit()
                print(
                    f"[info] created index ix_{tablename}_{col} "
                    f"on {schema}.{tablename}({col})",
                    file=sys.stderr,
                )
            except Exception as exc:
                conn.rollback()
                print(
                    f"[warn] failed to create index ix_{tablename}_{col} "
                    f"on {schema}.{tablename}({col}): {exc}",
                    file=sys.stderr,
                )


# ---------------------------------------------------------------------------
# COPY loading
# ---------------------------------------------------------------------------


def _seconds_to_time(v: Any) -> Optional[dt.time]:
    if v is None:
        return None
    if isinstance(v, float) and pd.isna(v):
        return None
    if isinstance(v, dt.time):
        return v
    if isinstance(v, (dt.datetime, pd.Timestamp)):
        return v.time() if not pd.isna(v) else None
    try:
        total = int(round(float(v)))
    except (TypeError, ValueError):
        return None
    h, rem = divmod(total, 3600)
    m, s = divmod(rem, 60)
    # Clamp; TIME8. is always within a day.
    h = max(0, min(h, 23))
    return dt.time(h, m, s)


def _prepare_for_copy(df: pd.DataFrame, columns: Dict[str, ColumnSpec]) -> pd.DataFrame:
    """Materialize a copy of ``df`` with each column in the right shape for
    ``to_csv`` so the CSV lands as valid input for the target Postgres type.

    Per-column conversions are vectorized (``.astype`` / ``pd.to_datetime`` /
    ``.mask`` / ``.fillna``) instead of the element-wise ``.map(func)``
    loops this function used to run. That was the single largest per-chunk
    CPU cost on text-heavy loads - a 40-column × 100k-row chunk was issuing
    ~4M Python-level function calls just to cast strings. TIME columns are
    still the ``.map`` path because SAS TIME8 is stored as seconds and the
    clamp-to-24h logic doesn't fit cleanly in vector form; they're also
    rare in practice.
    """
    out = pd.DataFrame(index=df.index)
    for name, spec in columns.items():
        series = df[name]
        pg = spec.postgres_type.upper()

        if pg in ("INTEGER", "BIGINT", "SMALLINT"):
            if pd.api.types.is_object_dtype(series):
                series = pd.to_numeric(
                    series.replace({"": None}), errors="coerce"
                )
            out[name] = series.astype("Int64")
        elif pg in ("DOUBLE PRECISION", "REAL", "NUMERIC"):
            if pd.api.types.is_object_dtype(series):
                series = pd.to_numeric(
                    series.replace({"": None}), errors="coerce"
                )
            out[name] = series.astype("float64")
        elif pg == "DATE":
            if pd.api.types.is_datetime64_any_dtype(series):
                out[name] = series.dt.date
            elif pd.api.types.is_object_dtype(series):
                # Vectorized parse: empty strings / None / unparseable -> NaT,
                # then .dt.date yields date objects or NaT. NaT serializes as
                # an empty CSV field (matching ``NULL ''`` in COPY).
                parsed = pd.to_datetime(
                    series.replace({"": None}), errors="coerce"
                )
                out[name] = parsed.dt.date
            elif pd.api.types.is_numeric_dtype(series):
                # pyreadstat couldn't decode the SAS format (some
                # ``DATEw.``/``YYMMDDw.`` variants and all custom formats slip
                # through) so the column came back as float64: days since
                # 1960-01-01, the SAS epoch. Without this branch the raw
                # number would hit COPY and Postgres rejects it with
                # ``invalid input syntax for type date``.
                parsed = pd.to_datetime(
                    series, unit="D", origin="1960-01-01", errors="coerce",
                )
                out[name] = parsed.dt.date
            else:
                out[name] = series
        elif pg in ("TIMESTAMP", "TIMESTAMP WITHOUT TIME ZONE", "TIMESTAMP WITH TIME ZONE"):
            if pd.api.types.is_datetime64_any_dtype(series):
                out[name] = series
            elif pd.api.types.is_object_dtype(series):
                out[name] = pd.to_datetime(
                    series.replace({"": None}), errors="coerce"
                )
            elif pd.api.types.is_numeric_dtype(series):
                # Same story as the DATE branch above, but SAS datetimes are
                # *seconds* since 1960-01-01 (fractional seconds for
                # ``DATETIMEw.d``). Example caught in the wild:
                # ``1915465463.615`` -> 2020-09-13 05:44:23.615.
                out[name] = pd.to_datetime(
                    series, unit="s", origin="1960-01-01", errors="coerce",
                )
            else:
                out[name] = series
        elif pg in ("TIME", "TIME WITHOUT TIME ZONE", "TIME WITH TIME ZONE"):
            out[name] = series.map(_seconds_to_time)
        elif pg in ("TEXT", "VARCHAR", "CHARACTER VARYING", "CHAR", "CHARACTER"):
            # Render every cell as a string and blank out nulls. ``NULL ''``
            # in the COPY statement turns the blanks back into SQL NULL.
            # astype(str) stringifies NaN/None to the literal "nan"/"None",
            # so we mask those after the fact rather than branching per cell.
            na_mask = series.isna()
            out[name] = series.astype(str).mask(na_mask, "")
        elif pg == "BOOLEAN":
            out[name] = series.astype("boolean") if series.dtype != object else series
        else:
            out[name] = series
    return out


def _serialize_chunk_csv(prepared: pd.DataFrame) -> io.BytesIO:
    """Serialize a prepared frame into a CSV buffer for ``COPY FROM STDIN``.

    Uses ``pyarrow.csv.write_csv`` (typically 5-10× faster than pandas'
    pure-Python ``to_csv`` on wide/text-heavy frames). Null cells serialize
    as empty strings and date/timestamp values land in ISO 8601 form, both
    of which Postgres accepts under ``FORMAT csv, NULL ''``.
    """
    table = pa.Table.from_pandas(prepared, preserve_index=False)
    buf = io.BytesIO()
    pa_csv.write_csv(
        table,
        buf,
        write_options=pa_csv.WriteOptions(include_header=False),
    )
    buf.seek(0)
    return buf


def copy_dataframes(
    conn,
    schema_name: str,
    table_name: str,
    dfs: Iterable[pd.DataFrame],
    columns: Dict[str, ColumnSpec],
) -> int:
    """Stream an iterable of DataFrames into Postgres, committing each chunk.

    Each non-empty chunk is copied via ``COPY ... FROM STDIN`` and committed
    before the next chunk is processed, so an interrupted or failed load
    retains the rows from previously committed chunks. The first chunk's
    commit also flushes any pending DDL (e.g. a preceding ``CREATE TABLE``).
    Empty chunks are skipped. Returns the total rows inserted.
    """
    col_list = ", ".join(_quote_ident(name) for name in columns.keys())
    sql = (
        f"COPY {_qualified(schema_name, table_name)} ({col_list}) "
        f"FROM STDIN WITH (FORMAT csv, NULL '')"
    )

    total = 0
    with conn.cursor() as cur:
        for df in dfs:
            if df.empty:
                continue
            prepared = _prepare_for_copy(df, columns)
            buf = _serialize_chunk_csv(prepared)
            cur.copy_expert(sql, buf)
            conn.commit()
            total += len(prepared)
    return total


def copy_dataframe(
    conn,
    schema_name: str,
    table_name: str,
    df: pd.DataFrame,
    columns: Dict[str, ColumnSpec],
) -> int:
    """Stream ``df`` into Postgres via ``COPY ... FROM STDIN``.

    Convenience wrapper around :func:`copy_dataframes` for single-frame
    callers. Returns the number of rows inserted.
    """
    return copy_dataframes(conn, schema_name, table_name, [df], columns)


# ---------------------------------------------------------------------------
# Manifest validation
# ---------------------------------------------------------------------------


def _match_manifest_type(inferred: str, manifest_entry: Dict[str, Any]) -> bool:
    inferred_norm = _normalize_type(inferred)
    if "postgres_type" in manifest_entry:
        return inferred_norm == _normalize_type(manifest_entry["postgres_type"])
    if "acceptable_types" in manifest_entry:
        return any(
            inferred_norm == _normalize_type(t)
            for t in manifest_entry["acceptable_types"]
        )
    return False


def validate_against_manifest(
    inferred: Dict[str, ColumnSpec],
    manifest_path: Path,
) -> List[str]:
    """Compare the inferred schema against the expected-types manifest.

    Returns a list of human-readable problem strings; empty list means OK.
    """
    manifest_path = Path(manifest_path)
    if not manifest_path.exists():
        return [f"manifest not found: {manifest_path}"]

    with manifest_path.open("r", encoding="utf-8") as f:
        manifest = json.load(f)

    problems: List[str] = []

    only_in_inferred = set(inferred) - set(manifest)
    only_in_manifest = set(manifest) - set(inferred)
    if only_in_inferred:
        problems.append(
            f"columns in inferred but not manifest: {sorted(only_in_inferred)}"
        )
    if only_in_manifest:
        problems.append(
            f"columns in manifest but not inferred: {sorted(only_in_manifest)}"
        )

    for name, spec in inferred.items():
        entry = manifest.get(name)
        if entry is None:
            continue
        if not _match_manifest_type(spec.postgres_type, entry):
            expected = entry.get("postgres_type") or entry.get("acceptable_types")
            problems.append(
                f"column {name!r}: inferred {spec.postgres_type!r}, "
                f"manifest expected {expected!r}"
            )
        manifest_nullable = bool(entry.get("nullable", True))
        if spec.nullable and not manifest_nullable:
            problems.append(
                f"column {name!r}: inferred nullable, manifest expects NOT NULL "
                f"(loosening nullability is never allowed)"
            )

    return problems


# ---------------------------------------------------------------------------
# CLI
# ---------------------------------------------------------------------------


def _build_argparser() -> argparse.ArgumentParser:
    p = argparse.ArgumentParser(
        description="Load a single SAS file (XPT or sas7bdat) into Postgres.",
    )
    p.add_argument("--config", required=True, type=Path, help="Path to YAML config")
    p.add_argument(
        "--validate",
        action="store_true",
        help=(
            "Compare inferred schema against <filename-stem>.expected.json "
            "next to the SAS file; exits nonzero on mismatch."
        ),
    )
    p.add_argument(
        "--dry-run",
        action="store_true",
        help="Print inferred CREATE TABLE and stop; don't touch Postgres.",
    )
    p.add_argument(
        "--dbcreds",
        action="store_true",
        help=(
            "Prompt for database username and password instead of reading "
            "PGUSER / PGPASSWORD from the environment or .env file."
        ),
    )
    return p


def _format_columns_summary(columns: Dict[str, ColumnSpec]) -> str:
    lines = []
    for spec in columns.values():
        null = "" if spec.nullable else " NOT NULL"
        lines.append(f"  {spec.name}: {spec.postgres_type}{null}")
    return "\n".join(lines)


def main(argv: Optional[List[str]] = None) -> int:
    args = _build_argparser().parse_args(argv)

    load_dotenv()

    cfg = load_config(args.config)

    if not cfg.filename.exists():
        print(f"error: SAS file not found: {cfg.filename}", file=sys.stderr)
        return 2

    # Schema inference reads the whole file so type + nullability are
    # computed against every row. That's what the target host has the
    # resources for and is the only way to honestly emit ``NOT NULL`` -
    # a bounded preview routinely missed the ~0.2% of rows with nulls on
    # otherwise-dense keys (e.g. MAFID). If you're on a box that can't
    # fit the file in memory, override ``TYPE_INFERENCE_SAMPLE_ROWS`` to
    # an integer cap and know that sampled specs may stamp ``NOT NULL``
    # on columns whose nulls live past the window.
    preview_df, meta = read_sas_preview(cfg.filename)
    preview_df = apply_column_filter(preview_df, cfg.include, cfg.exclude)
    columns = infer_schema(preview_df, meta)

    # Validate partition columns exist in the schema after filtering.
    if cfg.partition_by:
        missing_pcols = [c for c in cfg.partition_by if c not in columns]
        if missing_pcols:
            raise ValueError(
                f"partition_by references columns not present in the "
                f"(filtered) schema: {missing_pcols}"
            )

    # Validate index columns exist in the schema after filtering.
    if cfg.indexes:
        missing_icols = [c for c in cfg.indexes if c not in columns]
        if missing_icols:
            raise ValueError(
                f"indexes references columns not present in the "
                f"(filtered) schema: {missing_icols}"
            )

    if args.validate:
        manifest_path = cfg.filename.with_suffix("").with_suffix(".expected.json")
        # The above strips .xpt then appends .expected.json, e.g.
        # "sample_kitchensink.xpt" -> "sample_kitchensink.expected.json".
        problems = validate_against_manifest(columns, manifest_path)
        if problems:
            print("validation failed:", file=sys.stderr)
            for p in problems:
                print(f"  - {p}", file=sys.stderr)
            return 1
        print(f"validation OK ({len(columns)} columns match {manifest_path.name})")

    # -- Partition value discovery ------------------------------------------
    # If partitioned, scan the ENTIRE file to discover all unique partition
    # values. The preview is only the first N rows and may miss values.
    # In append mode the partitions already exist, so skip the costly scan.
    partition_values: Optional[dict] = None
    if cfg.partition_by and cfg.if_exists != "append":
        print("  discovering partition values (full file scan)...", file=sys.stderr)

        def _discovery_chunks():
            for chunk_df, _chunk_meta in iter_sas_chunks(cfg.filename):
                yield apply_column_filter(chunk_df, cfg.include, cfg.exclude)

        partition_values = discover_partition_values_chunked(
            _discovery_chunks(), cfg.partition_by, columns,
        )
        total_parts = _count_partitions(partition_values)
        print(
            f"  discovered {total_parts:,} partition tables "
            f"across {len(cfg.partition_by)} level(s)",
            file=sys.stderr,
        )
    elif cfg.partition_by and cfg.if_exists == "append":
        print(
            "  [info] append mode: skipping partition discovery "
            "(partitions assumed to exist)",
            file=sys.stderr,
        )

    if args.dry_run:
        # Print the parent CREATE TABLE (with PARTITION BY if applicable).
        parent_ddl = render_create_table(
            cfg.schemaname, cfg.tablename, columns,
            partition_by=cfg.partition_by or None,
        )
        print(parent_ddl)
        # Print child partition DDL if partitioned.
        if cfg.partition_by and partition_values:
            child_stmts = render_partition_ddl(
                cfg.schemaname, cfg.tablename, cfg.partition_by,
                partition_values, columns,
                max_partitions=cfg.max_partitions,
            )
            for stmt in child_stmts:
                print()
                print(stmt)
        # Print CREATE INDEX DDL if indexes are configured.
        if cfg.indexes:
            idx_stmts = render_create_indexes(
                cfg.schemaname, cfg.tablename, cfg.indexes,
            )
            for stmt in idx_stmts:
                print()
                print(stmt)
        return 0

    # Release the preview frame before opening the stream - lets the GC reclaim
    # it while we're holding a Postgres transaction open.
    del preview_df

    total_rows = getattr(meta, "number_rows", None)

    def _filtered_chunks():
        pbar = tqdm(
            total=total_rows,
            unit="row",
            unit_scale=True,
            desc=f"  {cfg.filename.name}",
            file=sys.stderr,
            dynamic_ncols=True,
        )
        try:
            for chunk_df, _chunk_meta in iter_sas_chunks(cfg.filename):
                chunk_df = apply_column_filter(chunk_df, cfg.include, cfg.exclude)
                pbar.update(len(chunk_df))
                yield chunk_df
        finally:
            pbar.close()

    db_user = db_password = None
    if args.dbcreds:
        db_user = input("Database username: ")
        db_password = getpass.getpass("Database password: ")

    conn = connect(user=db_user, password=db_password)
    conn.autocommit = False
    try:
        create_table(
            conn, cfg.schemaname, cfg.tablename, columns, cfg.if_exists,
            partition_by=cfg.partition_by or None,
            partition_values=partition_values,
            max_partitions=cfg.max_partitions,
        )
        inserted = copy_dataframes(
            conn, cfg.schemaname, cfg.tablename, _filtered_chunks(), columns
        )
        conn.commit()
        if cfg.indexes:
            create_indexes(conn, cfg.schemaname, cfg.tablename, cfg.indexes)
    except Exception:
        conn.rollback()
        raise
    finally:
        conn.close()

    print(
        f"loaded {inserted} rows into {cfg.schemaname}.{cfg.tablename} "
        f"({len(columns)} columns)"
    )
    if cfg.partition_by and partition_values:
        total_parts = _count_partitions(partition_values)
        print(f"partitioned by {cfg.partition_by} ({total_parts:,} partition tables)")
    print("final schema:")
    print(_format_columns_summary(columns))
    return 0


if __name__ == "__main__":
    sys.exit(main())