"""Disk-based metadata cache + thread-safe in-memory container for background generation."""
from __future__ import annotations

import hashlib
import json
import logging
import threading
from pathlib import Path

logger = logging.getLogger(__name__)

# Cache directory local to the project
CACHE_DIR = Path(__file__).resolve().parent.parent / ".cache" / "metadata"

# Cache version — bump this when the metadata format changes to invalidate old caches.
# v2: switched page_num from 0-indexed to 1-indexed
# v3: removed related_legends, has_title_block, title_block_text; parallel batch generation
_CACHE_VERSION = "v3"


def _pdf_hash(pdf_bytes: bytes) -> str:
    """Compute a SHA-256 hash of the PDF bytes for cache keying."""
    return hashlib.sha256(pdf_bytes).hexdigest()


def get_cached_metadata(pdf_bytes: bytes) -> list[dict] | None:
    """Check if metadata exists on disk for the given PDF.

    Returns the metadata list if found, None otherwise.
    """
    cache_path = CACHE_DIR / f"{_pdf_hash(pdf_bytes)}_{_CACHE_VERSION}.json"
    if cache_path.exists():
        try:
            return json.loads(cache_path.read_text(encoding="utf-8"))
        except (json.JSONDecodeError, OSError):
            return None
    return None


def save_metadata(pdf_bytes: bytes, metadata_list: list[dict]) -> None:
    """Save metadata to disk, keyed by PDF hash."""
    CACHE_DIR.mkdir(parents=True, exist_ok=True)
    cache_path = CACHE_DIR / f"{_pdf_hash(pdf_bytes)}_{_CACHE_VERSION}.json"
    cache_path.write_text(
        json.dumps(metadata_list, indent=2),
        encoding="utf-8",
    )


class MetadataState:
    """Thread-safe container for background metadata generation state.

    Stored as a single object in ``st.session_state``.  The background thread
    mutates fields on *this same object* (safe under CPython's GIL for simple
    attribute assignments).  The main Streamlit thread reads from it on each
    rerun.
    """

    def __init__(self) -> None:
        self.status: str = "not_started"  # not_started | in_progress | ready | failed
        self.data_json: str = ""          # pre-serialized JSON for the planner
        self.error: str | None = None
        self._lock = threading.Lock()

    # -- convenience helpers --------------------------------------------------

    def set_ready(self, data_json: str) -> None:
        with self._lock:
            self.data_json = data_json
            self.status = "ready"

    def set_failed(self, error: str) -> None:
        with self._lock:
            self.error = error
            self.status = "failed"

    def set_in_progress(self) -> None:
        with self._lock:
            self.status = "in_progress"

    @property
    def is_ready(self) -> bool:
        return self.status == "ready"

    def generate_sync(
        self,
        pdf_path: str,
        num_pages: int,
        pdf_bytes: bytes,
        progress_callback=None,
    ) -> None:
        """Generate metadata synchronously (blocking).

        Same logic as ``start_background_generation`` but runs in the calling
        thread.  Used during initialization so metadata is ready before the
        user can ask questions.

        Args:
            progress_callback: Optional ``(completed, total, label) -> None``
                forwarded to ``generate_page_metadata`` for progress reporting.
        """
        self.set_in_progress()
        try:
            from nodes.metadata_generator import generate_page_metadata

            metadata_list = generate_page_metadata(
                pdf_path, num_pages, progress_callback=progress_callback,
            )
            save_metadata(pdf_bytes, metadata_list)
            self.set_ready(json.dumps(metadata_list, indent=2))
            logger.info("Metadata generation complete.")
        except Exception as e:
            self.set_failed(str(e))
            logger.exception("Metadata generation failed")

    def start_background_generation(
        self,
        pdf_path: str,
        num_pages: int,
        pdf_bytes: bytes,
    ) -> None:
        """Launch a daemon thread that generates metadata and writes to disk cache."""
        self.set_in_progress()

        def _run():
            try:
                from nodes.metadata_generator import generate_page_metadata

                metadata_list = generate_page_metadata(pdf_path, num_pages)
                save_metadata(pdf_bytes, metadata_list)
                self.set_ready(json.dumps(metadata_list, indent=2))
                logger.info("Background metadata generation complete.")
            except Exception as e:
                self.set_failed(str(e))
                logger.exception("Background metadata generation failed")

        thread = threading.Thread(target=_run, daemon=True)
        thread.start()