"""PDF text extraction and chunking for RAG."""
import re
from pathlib import Path
from typing import List

import pdfplumber
from pypdf import PdfReader

from config import CHUNK_OVERLAP, CHUNK_SIZE


def extract_text_from_pdf(pdf_path: str | Path) -> str:
    """Extract text from a PDF using pdfplumber (better for tables) with pypdf fallback."""
    path = Path(pdf_path)
    if not path.exists():
        raise FileNotFoundError(f"PDF not found: {path}")

    text_parts: List[str] = []
    try:
        with pdfplumber.open(path) as pdf:
            for page in pdf.pages:
                t = page.extract_text()
                if t:
                    text_parts.append(t)
    except Exception:
        # Fallback to pypdf
        reader = PdfReader(path)
        for page in reader.pages:
            t = page.extract_text()
            if t:
                text_parts.append(t)

    raw = "\n\n".join(text_parts)
    # Normalize whitespace
    return re.sub(r"\s+", " ", raw).strip()


def chunk_text(
    text: str,
    chunk_size: int = CHUNK_SIZE,
    overlap: int = CHUNK_OVERLAP,
) -> List[dict]:
    """
    Split text into overlapping chunks for embedding.
    Returns list of dicts with 'text' and 'metadata' (source, chunk_index).
    """
    if not text or not text.strip():
        return []

    chunks: List[dict] = []
    start = 0
    index = 0
    text = text.strip()

    while start < len(text):
        end = start + chunk_size
        chunk = text[start:end]

        # Try to break at sentence or word boundary
        if end < len(text):
            last_period = chunk.rfind(". ")
            last_newline = chunk.rfind("\n")
            break_at = max(last_period, last_newline)
            if break_at > chunk_size // 2:
                chunk = chunk[: break_at + 1]
                end = start + break_at + 1

        chunk = chunk.strip()
        if chunk:
            chunks.append({
                "text": chunk,
                "metadata": {"chunk_index": index},
            })
            index += 1

        start = end - overlap if end < len(text) else len(text)

    return chunks


def process_pdf(pdf_path: str | Path, source_name: str | None = None) -> List[dict]:
    """
    Extract text from PDF and return chunks with source metadata.
    source_name: optional label (e.g. filename) for metadata.
    """
    path = Path(pdf_path)
    source_name = source_name or path.name
    text = extract_text_from_pdf(path)
    chunks = chunk_text(text)
    for c in chunks:
        c["metadata"]["source"] = source_name
    return chunks