from __future__ import annotations

import os
from datetime import datetime
from typing import List, Dict, Any


def extract_metadata(file_path: str, chunks: List[str], original_filename: str | None = None) -> List[Dict[str, Any]]:
    """Extract metadata for a list of text chunks.

    For each chunk, create a metadata dictionary containing:
    - filename: basename of the provided file_path (or original_filename if provided)
    - upload_date: ISO 8601 timestamp of when metadata was generated
    - content_summary: first 200 characters of the chunk (or full chunk if shorter)
    - chunk_index: 0-based index of the chunk

    Args:
        file_path: Path to the file associated with the chunks.
        chunks: List of string chunks to generate metadata for.
        original_filename: Override filename stored in metadata when file_path
            is a temp file.

    Returns:
        A list of metadata dictionaries, one per chunk. If chunks is empty, returns an empty list.

    Raises:
        FileNotFoundError: If the provided file_path does not exist.
    """

    # Edge case: no chunks to metadataize
    if not chunks:
        return []

    # Validate file existence up-front to follow the edge-case requirements
    if not os.path.exists(file_path):
        raise FileNotFoundError(f"File not found: {file_path}")

    filename = original_filename if original_filename else os.path.basename(file_path)
    upload_date = datetime.now().isoformat()

    metadata: List[Dict[str, Any]] = []
    for idx, chunk in enumerate(chunks):
        # Ensure we always have a string for summary extraction
        text = chunk if isinstance(chunk, str) else ""
        content_summary = text[:200]
        metadata.append(
            {
                "filename": filename,
                "upload_date": upload_date,
                "content_summary": content_summary,
                "chunk_index": idx,
            }
        )

    return metadata