"""Explore S3 directories and categorise them by accessibility.

Reads a text file containing one S3 prefix per line (paths within the bucket
configured by the ``S3_BUCKET`` constant), then for each prefix:
- Lists all objects recursively (via ``list_objects_v2`` paginator)
- **Only considers files matching the ``FILE_EXTENSION`` filter** (default
  ``.sas7bdat``).  All other file types are ignored.
- Tests read permission with ``head_object`` on the first matching file found
- If the first file is accessible, tests ALL remaining files individually
- Categorises the directory as **Available**, **Blocked**, **Empty**, and
  tracks individual file **Exceptions** within available directories

A directory is considered *empty* if it contains no files matching the
extension filter, even when other file types are present.

Configure the constants below, then run::

    python3 data_explorer.py

Python 3.10+ compatible.  Requires only ``boto3`` / ``botocore`` and stdlib.
"""

from __future__ import annotations

import sys
from dataclasses import dataclass, field
from typing import List, Tuple

# ---------------------------------------------------------------------------
# Dependency check
# ---------------------------------------------------------------------------

try:
    import boto3  # noqa: F401
    import botocore.exceptions  # noqa: F401
except ImportError:
    print(
        "ERROR: boto3 / botocore is not installed.\n"
        "Install with:  pip install boto3",
        file=sys.stderr,
    )
    sys.exit(1)


# ---------------------------------------------------------------------------
# Configuration — edit these before running
# ---------------------------------------------------------------------------

FILE_EXTENSION: str = ".sas7bdat"
"""Only files whose key ends with this extension (case-insensitive) are considered."""

INPUT_FILE: str = "s3_directories.txt"
"""Path to the text file containing one S3 prefix per line."""

S3_BUCKET: str = "my-bucket"
"""S3 bucket name (all prefixes are assumed to live in this bucket)."""

AWS_PROFILE: str = "default"
"""AWS CLI profile name used for authentication."""


# ---------------------------------------------------------------------------
# Data structures
# ---------------------------------------------------------------------------


@dataclass
class AvailableDir:
    """An S3 directory that is readable."""

    prefix: str
    file_count: int
    total_size: int  # bytes
    accessible_count: int = 0   # files that passed head_object
    total_count: int = 0        # total .sas7bdat files found
    accessible_size: int = 0    # total size of accessible files only


@dataclass
class BlockedDir:
    """An S3 directory where access was denied or an error occurred."""

    prefix: str
    file_count: int
    error: str


@dataclass
class EmptyDir:
    """An S3 directory with no objects."""

    prefix: str


@dataclass
class ExceptionFile:
    """A specific file that failed permission check within an otherwise available directory."""

    prefix: str   # the directory prefix
    key: str      # the full S3 key of the failed file
    error: str    # the error message


@dataclass
class Results:
    """Aggregated exploration results."""

    available: List[AvailableDir] = field(default_factory=list)
    blocked: List[BlockedDir] = field(default_factory=list)
    empty: List[EmptyDir] = field(default_factory=list)
    exceptions: List[ExceptionFile] = field(default_factory=list)


# ---------------------------------------------------------------------------
# Helpers
# ---------------------------------------------------------------------------


def read_input_file(path: str) -> List[str]:
    """Return a list of S3 prefixes from *path*, ignoring blanks and comments.

    Each line is stripped and normalised so that non-empty prefixes always end
    with a trailing ``/``.
    """
    prefixes: List[str] = []
    with open(path, encoding="utf-8") as fh:
        for raw_line in fh:
            line = raw_line.strip()
            if not line or line.startswith("#"):
                continue
            # Normalise: strip surrounding whitespace/slashes, then re-add
            # a single trailing slash (unless the prefix is empty/root).
            line = line.strip("/")
            if line:
                line += "/"
            prefixes.append(line)
    return prefixes


def format_size(size_bytes: int) -> str:
    """Return a human-readable size string (KB, MB, GB, TB)."""
    if size_bytes < 1024:
        return f"{size_bytes} B"
    for unit in ("KB", "MB", "GB", "TB"):
        size_bytes /= 1024.0
        if size_bytes < 1024.0 or unit == "TB":
            return f"{size_bytes:,.1f} {unit}"
    # Fallback (should not be reached)
    return f"{size_bytes:,.1f} TB"


def list_objects(
    s3_client: "botocore.client.S3",
    bucket: str,
    prefix: str,
) -> Tuple[List[Tuple[str, int]], int]:
    """Recursively list all objects under *prefix*.

    Only objects whose key ends with ``FILE_EXTENSION`` (case-insensitive) are
    counted.  All other files are silently skipped.

    Returns ``(files, total_size)`` where *files* is a list of
    ``(key, size)`` tuples for every matching object and *total_size* is the
    sum of their sizes in bytes.
    """
    ext_lower = FILE_EXTENSION.lower()
    paginator = s3_client.get_paginator("list_objects_v2")
    files: List[Tuple[str, int]] = []
    total_size: int = 0
    for page in paginator.paginate(Bucket=bucket, Prefix=prefix):
        for obj in page.get("Contents", []):
            if not obj["Key"].lower().endswith(ext_lower):
                continue
            files.append((obj["Key"], obj["Size"]))
            total_size += obj["Size"]
    return files, total_size


def check_read_permission(
    s3_client: "botocore.client.S3",
    bucket: str,
    key: str,
) -> str | None:
    """Try ``head_object`` on *key*.  Return ``None`` on success or an error string."""
    try:
        s3_client.head_object(Bucket=bucket, Key=key)
    except botocore.exceptions.ClientError as exc:
        code = exc.response.get("Error", {}).get("Code", "Unknown")
        message = exc.response.get("Error", {}).get("Message", str(exc))
        return f"{message} ({code})"
    return None


# ---------------------------------------------------------------------------
# Core logic
# ---------------------------------------------------------------------------


def explore_directories(prefixes: List[str]) -> Results:
    """Explore every prefix in ``S3_BUCKET`` and return categorised *Results*."""
    session = boto3.Session(profile_name=AWS_PROFILE)
    s3 = session.client("s3")

    results = Results()
    total = len(prefixes)

    for idx, prefix in enumerate(prefixes, start=1):
        print(
            f"[{idx}/{total}] Checking {prefix} (filtering for {FILE_EXTENSION}) ...",
            file=sys.stderr,
        )

        # --- Recursive listing ------------------------------------------------
        try:
            files, total_size = list_objects(s3, S3_BUCKET, prefix)
        except botocore.exceptions.ClientError as exc:
            code = exc.response.get("Error", {}).get("Code", "Unknown")
            message = exc.response.get("Error", {}).get("Message", str(exc))
            results.blocked.append(
                BlockedDir(prefix=prefix, file_count=0, error=f"{message} ({code})")
            )
            continue
        except Exception as exc:
            results.blocked.append(
                BlockedDir(prefix=prefix, file_count=0, error=str(exc))
            )
            continue

        if not files:
            results.empty.append(EmptyDir(prefix=prefix))
            continue

        file_count = len(files)

        # --- Permission check on first file -----------------------------------
        # Prefer a real object over a zero-byte directory marker (key ending
        # in "/") for the head_object test.
        first_key, _ = files[0]
        test_key = first_key
        if first_key.endswith("/") and total_size > 0:
            for key, size in files:
                if not (key.endswith("/") and size == 0):
                    test_key = key
                    break

        error = check_read_permission(s3, S3_BUCKET, test_key)
        if error is not None:
            # First file blocked → entire directory is blocked
            results.blocked.append(
                BlockedDir(prefix=prefix, file_count=file_count, error=error)
            )
            continue

        # --- First file accessible → check ALL remaining files ----------------
        accessible_count = 1  # the first (test_key) already passed
        accessible_size = 0
        dir_exceptions: List[ExceptionFile] = []

        # Find the size of the test_key to count it
        for key, size in files:
            if key == test_key:
                accessible_size = size
                break

        # Build list of remaining files to check
        remaining = [(key, size) for key, size in files if key != test_key]

        if remaining:
            if len(remaining) > 10:
                print(
                    f"  Verifying access to {file_count} {FILE_EXTENSION} files in {prefix} ...",
                    file=sys.stderr,
                )

            for key, size in remaining:
                file_error = check_read_permission(s3, S3_BUCKET, key)
                if file_error is None:
                    accessible_count += 1
                    accessible_size += size
                else:
                    dir_exceptions.append(
                        ExceptionFile(prefix=prefix, key=key, error=file_error)
                    )

        else:
            # Only one file and it passed
            accessible_size = total_size

        results.available.append(
            AvailableDir(
                prefix=prefix,
                file_count=file_count,
                total_size=total_size,
                accessible_count=accessible_count,
                total_count=file_count,
                accessible_size=accessible_size,
            )
        )
        results.exceptions.extend(dir_exceptions)

    return results


# ---------------------------------------------------------------------------
# Output
# ---------------------------------------------------------------------------


def print_results(results: Results) -> None:
    """Print a clean, human-readable summary to stdout."""
    print()
    print("=== S3 Directory Explorer Results ===")
    print(f"Bucket: {S3_BUCKET}")

    # --- Available ---
    print()
    print(f"--- Available ({len(results.available)}) ---")
    if results.available:
        for d in results.available:
            print(f"  {d.prefix}")
            print(
                f"    {FILE_EXTENSION} files: {d.accessible_count}/{d.total_count} accessible"
                f" | Total Size: {format_size(d.accessible_size)}"
            )
    else:
        print("  (none)")

    # --- Blocked ---
    print()
    print(f"--- Blocked ({len(results.blocked)}) ---")
    if results.blocked:
        for d in results.blocked:
            if d.file_count:
                print(f"  {d.prefix}")
                print(f"    {FILE_EXTENSION} files found: {d.file_count} | Error: {d.error}")
            else:
                print(f"  {d.prefix}")
                print(f"    Error: {d.error}")
    else:
        print("  (none)")

    # --- Exceptions ---
    print()
    print(f"--- Exceptions ({len(results.exceptions)}) ---")
    if results.exceptions:
        for exc in results.exceptions:
            print(f"  {exc.key}")
            print(f"    Directory: {exc.prefix} | Error: {exc.error}")
    else:
        print("  (none)")

    # --- Empty ---
    print()
    print(f"--- Empty / no {FILE_EXTENSION} files ({len(results.empty)}) ---")
    if results.empty:
        for d in results.empty:
            print(f"  {d.prefix}")
    else:
        print("  (none)")

    print()


# ---------------------------------------------------------------------------
# Main
# ---------------------------------------------------------------------------

if __name__ == "__main__":
    import os

    # --- Read input file ------------------------------------------------------
    if not os.path.exists(INPUT_FILE):
        print(f"ERROR: Input file not found: {INPUT_FILE}", file=sys.stderr)
        sys.exit(1)

    try:
        prefixes = read_input_file(INPUT_FILE)
    except Exception as exc:
        print(f"ERROR: Could not read input file: {exc}", file=sys.stderr)
        sys.exit(1)

    if not prefixes:
        print("No valid S3 prefixes found in the input file. Nothing to do.")
        sys.exit(0)

    # --- Validate AWS profile -------------------------------------------------
    try:
        session = boto3.Session(profile_name=AWS_PROFILE)
        # Force credential resolution to catch bad profiles early
        credentials = session.get_credentials()
        if credentials is None:
            raise RuntimeError(
                f"No credentials found for AWS profile {AWS_PROFILE!r}"
            )
    except botocore.exceptions.ProfileNotFound as exc:
        print(f"ERROR: {exc}", file=sys.stderr)
        sys.exit(1)
    except Exception as exc:
        print(f"ERROR: AWS profile validation failed: {exc}", file=sys.stderr)
        sys.exit(1)

    # --- Explore --------------------------------------------------------------
    print(f"Bucket: {S3_BUCKET}", file=sys.stderr)
    results = explore_directories(prefixes)
    print_results(results)