"""Sample gallery: ordered manifest + lazy thumbnail cache.

Backs the ``GET /api/samples`` and ``GET /api/samples/{id}/thumbnail``
endpoints. The manifest lives at ``samples/manifest.json``; the actual
``.tif`` images sit beside it. Thumbnails are generated on first request
and cached in memory for the process lifetime - no per-request disk I/O.
"""

from __future__ import annotations

import json
from pathlib import Path

import cv2


THUMBNAIL_SIZE: int = 128
THUMBNAIL_JPEG_QUALITY: int = 85


class SampleLibrary:
    """In-memory sample registry built from ``manifest.json``."""

    def __init__(self, base_dir: Path, entries: list[dict]) -> None:
        self._base_dir = base_dir
        self._entries: list[dict] = entries
        self._by_id: dict[str, dict] = {e["id"]: e for e in entries}
        self._thumb_cache: dict[str, bytes] = {}

    @classmethod
    def from_directory(cls, dir_path: str) -> "SampleLibrary":
        """Read ``<dir_path>/manifest.json`` and validate every referenced file.

        Raises:
            FileNotFoundError: If the manifest or any referenced ``.tif``
                is missing.
            ValueError: If the manifest is malformed.
        """
        base = Path(dir_path)
        manifest_path = base / "manifest.json"
        if not manifest_path.exists():
            raise FileNotFoundError(f"Sample manifest missing: {manifest_path}")

        with manifest_path.open("r", encoding="utf-8") as f:
            data = json.load(f)

        if not isinstance(data, dict) or "samples" not in data:
            raise ValueError(f"Malformed manifest at {manifest_path}: missing 'samples' key.")
        entries: list[dict] = data["samples"]
        if not isinstance(entries, list) or not entries:
            raise ValueError(f"Malformed manifest at {manifest_path}: empty sample list.")

        seen_ids: set[str] = set()
        for e in entries:
            for k in ("id", "label", "organ", "filename"):
                if k not in e:
                    raise ValueError(f"Sample entry missing '{k}': {e}")
            if e["id"] in seen_ids:
                raise ValueError(f"Duplicate sample id: {e['id']!r}")
            seen_ids.add(e["id"])
            tif_path = base / e["filename"]
            if not tif_path.exists():
                raise FileNotFoundError(
                    f"Sample file missing for id={e['id']!r}: {tif_path}"
                )
        return cls(base_dir=base, entries=entries)

    def list(self) -> list[dict]:
        """JSON-serializable list of sample metadata (without file paths)."""
        return [
            {"id": e["id"], "label": e["label"], "organ": e["organ"]}
            for e in self._entries
        ]

    def load_bytes(self, sample_id: str) -> bytes:
        """Return raw file bytes for the given sample id.

        Raises:
            KeyError: If ``sample_id`` is not in the manifest.
        """
        entry = self._by_id.get(sample_id)
        if entry is None:
            raise KeyError(sample_id)
        path = self._base_dir / entry["filename"]
        return path.read_bytes()

    def thumbnail(self, sample_id: str) -> bytes:
        """128x128 JPEG thumbnail bytes; built and cached on first request.

        Raises:
            KeyError: If ``sample_id`` is not in the manifest.
        """
        cached = self._thumb_cache.get(sample_id)
        if cached is not None:
            return cached
        entry = self._by_id.get(sample_id)
        if entry is None:
            raise KeyError(sample_id)
        path = self._base_dir / entry["filename"]
        bgr = cv2.imread(str(path), cv2.IMREAD_COLOR)
        if bgr is None:
            raise ValueError(f"Could not decode sample image: {path}")

        h, w = bgr.shape[:2]
        side = min(h, w)
        y0 = (h - side) // 2
        x0 = (w - side) // 2
        crop = bgr[y0:y0 + side, x0:x0 + side]
        interp = cv2.INTER_AREA if side > THUMBNAIL_SIZE else cv2.INTER_CUBIC
        thumb = cv2.resize(crop, (THUMBNAIL_SIZE, THUMBNAIL_SIZE), interpolation=interp)

        ok, buf = cv2.imencode(
            ".jpg", thumb, [cv2.IMWRITE_JPEG_QUALITY, THUMBNAIL_JPEG_QUALITY]
        )
        if not ok:
            raise RuntimeError(f"Could not JPEG-encode thumbnail for {sample_id}.")
        out = buf.tobytes()
        self._thumb_cache[sample_id] = out
        return out

    def has(self, sample_id: str) -> bool:
        """True if a sample with this id exists in the manifest."""
        return sample_id in self._by_id

    def __len__(self) -> int:  # pragma: no cover - convenience for logs
        return len(self._entries)