"""Document extraction — PDF / EPUB / Markdown / plain text.

Extracts ``(title, text)`` from every supported format. Structural
headers are preserved in the extracted text (PDF pages become
``## Page N`` headings, EPUB chapters are joined with rules) so the
chunker can attribute each chunk to its section.

All third-party parsers are imported lazily inside the extract methods:
the GUI must launch and probe on a bare system where EbookLib or pypdf
are not installed, and fail with an actionable message only when the
matching file type is actually encountered.
"""

from __future__ import annotations

import re
from pathlib import Path

# Source files ingested verbatim as language-tagged code blocks.
CODE_LANGUAGES: dict[str, str] = {
    ".py": "python", ".sh": "bash", ".bash": "bash", ".zsh": "zsh",
    ".yaml": "yaml", ".yml": "yaml", ".toml": "toml", ".ini": "ini",
    ".conf": "ini", ".cfg": "ini", ".json": "json", ".sql": "sql",
    ".rs": "rust", ".go": "go", ".c": "c", ".h": "c", ".cpp": "cpp",
    ".js": "javascript", ".ts": "typescript", ".tf": "hcl", ".nix": "nix",
}

SUPPORTED_EXTENSIONS = frozenset(
    {".pdf", ".epub", ".md", ".markdown", ".txt"}
    | set(CODE_LANGUAGES)
)


class ExtractionError(Exception):
    """Raised when a document cannot be parsed (missing dep, bad file)."""


def scan_files(
    input_dir: Path,
    extensions: frozenset[str] | set[str] = SUPPORTED_EXTENSIONS,
) -> list[Path]:
    """Recursively list supported documents under *input_dir*, sorted
    for deterministic queue order."""
    return sorted(
        (p for p in input_dir.rglob("*")
         if p.is_file() and p.suffix.lower() in extensions),
        key=lambda p: str(p).lower(),
    )


def _title_from_stem(filepath: Path) -> str:
    return filepath.stem.replace("-", " ").replace("_", " ").title()


class DocumentExtractor:
    """Extracts raw text and structural headers from supported formats."""

    @staticmethod
    def extract(filepath: Path) -> tuple[str, str]:
        """Dispatch on extension via the runner table. Raises
        ExtractionError for unsupported types or missing parser
        dependencies."""
        runner = _EXTENSION_RUNNERS.get(filepath.suffix.lower())
        if runner is None:
            raise ExtractionError(f"unsupported file type: {filepath.suffix}")
        return runner(filepath)

    @staticmethod
    def extract_md_txt(filepath: Path) -> tuple[str, str]:
        text = filepath.read_text(encoding="utf-8", errors="ignore")
        return _title_from_stem(filepath), text

    @staticmethod
    def extract_code(filepath: Path) -> tuple[str, str]:
        """Source/config file: verbatim content wrapped in a
        language-tagged fence so the chunker treats it as one code
        document and the vault note renders it as a listing."""
        lang = CODE_LANGUAGES.get(filepath.suffix.lower(), "")
        body = filepath.read_text(encoding="utf-8", errors="ignore")
        return _title_from_stem(filepath), f"```{lang}\n{body}\n```"

    @staticmethod
    def extract_pdf(filepath: Path) -> tuple[str, str]:
        try:
            from pypdf import PdfReader
        except ImportError as e:
            raise ExtractionError(
                "pypdf not installed — run: pip install 'thicket[ingest]'"
            ) from e

        reader = PdfReader(str(filepath))
        title = _title_from_stem(filepath)

        # Prefer the embedded metadata title when present.
        try:
            if reader.metadata and reader.metadata.title:
                title = str(reader.metadata.title).strip() or title
        except Exception:
            pass  # malformed metadata must not kill the extract

        pages_text: list[str] = []
        for i, page in enumerate(reader.pages):
            try:
                txt = page.extract_text() or ""
            except Exception:
                txt = ""
            if txt.strip():
                pages_text.append(f"## Page {i + 1}\n\n{txt}")

        return title, "\n\n".join(pages_text)

    @staticmethod
    def extract_epub(filepath: Path) -> tuple[str, str]:
        try:
            import bs4
            from ebooklib import epub, ITEM_DOCUMENT
        except ImportError as e:
            raise ExtractionError(
                "ebooklib / beautifulsoup4 not installed — run: "
                "pip install 'thicket[ingest]'"
            ) from e

        book = epub.read_epub(str(filepath))
        title = _title_from_stem(filepath)

        meta_titles = book.get_metadata("DC", "title")
        if meta_titles:
            title = str(meta_titles[0][0]).strip() or title

        chapters: list[str] = []
        for item in book.get_items_of_type(ITEM_DOCUMENT):
            soup = bs4.BeautifulSoup(item.get_content(), "html.parser")
            text = soup.get_text(separator="\n")
            clean_text = re.sub(r"\n+", "\n", text).strip()
            if clean_text:
                chapters.append(clean_text)

        return title, "\n\n---\n\n".join(chapters)

# Extension dispatch table — the single source of routing for extract().
# Adding a format means adding one entry here and its extractor method.
_EXTENSION_RUNNERS: dict[str, object] = {
    ".md": DocumentExtractor.extract_md_txt,
    ".markdown": DocumentExtractor.extract_md_txt,
    ".txt": DocumentExtractor.extract_md_txt,
    ".pdf": DocumentExtractor.extract_pdf,
    ".epub": DocumentExtractor.extract_epub,
    **{ext: DocumentExtractor.extract_code for ext in CODE_LANGUAGES},
}