"""Snapshot persistence -- save, list, and select validated snapshots.

Validated snapshots are stored as frozen JSON under ``snapshots/<id>/spec.json``.
The store supports selection strategies for ``reset()`` to draw from a pool of
pre-validated snapshots rather than generating on-demand.
"""

from __future__ import annotations

import json
import logging
import random
import time
from dataclasses import dataclass
from pathlib import Path
from typing import Any

from open_range.protocols import SnapshotSpec

logger = logging.getLogger(__name__)


@dataclass(frozen=True, slots=True)
class StoredSnapshot:
    """A frozen snapshot plus its persisted identifier."""

    snapshot_id: str
    snapshot: SnapshotSpec


class SnapshotStore:
    """Persist and retrieve validated snapshot specs."""

    def __init__(self, store_dir: str = "snapshots") -> None:
        self.store_dir = Path(store_dir)
        self.store_dir.mkdir(parents=True, exist_ok=True)

    async def store(self, snapshot: SnapshotSpec, snapshot_id: str | None = None) -> str:
        """Save a validated snapshot to disk.

        Args:
            snapshot: The validated snapshot spec.
            snapshot_id: Optional explicit ID. Generated from topology if absent.

        Returns:
            The snapshot ID string.
        """
        if snapshot_id is None:
            vuln_types = [v.type for v in snapshot.truth_graph.vulns]
            snapshot_id = (
                f"snap_{'_'.join(vuln_types[:3])}"
                f"_{int(time.time())}"
            )

        snap_dir = self.store_dir / snapshot_id
        snap_dir.mkdir(parents=True, exist_ok=True)

        spec_path = snap_dir / "spec.json"
        spec_path.write_text(
            snapshot.model_dump_json(indent=2),
            encoding="utf-8",
        )

        # Write metadata sidecar for fast listing
        meta = self._metadata_from_snapshot(snapshot_id, snapshot)
        meta_path = snap_dir / "metadata.json"
        meta_path.write_text(json.dumps(meta, indent=2), encoding="utf-8")

        logger.info("Stored snapshot %s at %s", snapshot_id, snap_dir)
        return snapshot_id

    async def select(self, strategy: str = "latest") -> SnapshotSpec:
        """Select a snapshot from the store.

        Args:
            strategy: Selection strategy.
                - ``"latest"``: most recently stored snapshot
                - ``"random"``: uniformly random

        Returns:
            The selected SnapshotSpec.

        Raises:
            FileNotFoundError: If the store is empty.
        """
        return (await self.select_entry(strategy=strategy)).snapshot

    async def select_entry(self, strategy: str = "latest") -> StoredSnapshot:
        """Select a snapshot plus its persisted ID."""
        spec_files = sorted(self.store_dir.glob("*/spec.json"))
        if not spec_files:
            raise FileNotFoundError(
                f"No snapshots in store: {self.store_dir}"
            )

        if strategy == "random":
            chosen = random.choice(spec_files)
        else:  # latest -- sort by parent dir mtime
            chosen = max(spec_files, key=lambda p: p.stat().st_mtime)

        return StoredSnapshot(
            snapshot_id=chosen.parent.name,
            snapshot=self._load_spec(chosen),
        )

    async def list_entries(self) -> list[StoredSnapshot]:
        """Return every stored snapshot plus its persisted ID."""
        entries: list[StoredSnapshot] = []
        for spec_path in sorted(self.store_dir.glob("*/spec.json")):
            entries.append(
                StoredSnapshot(
                    snapshot_id=spec_path.parent.name,
                    snapshot=self._load_spec(spec_path),
                )
            )
        return entries

    async def count_entries(self) -> int:
        """Return canonical snapshot count based on persisted specs."""
        return len(await self.list_entries())

    async def list_snapshots(self) -> list[dict[str, Any]]:
        """List all snapshots with their metadata.

        Returns:
            List of metadata dicts, sorted by stored_at descending.
        """
        entries = await self.list_entries()
        spec_ids = {entry.snapshot_id for entry in entries}
        results: list[dict[str, Any]] = []
        for entry in entries:
            meta_path = self.store_dir / entry.snapshot_id / "metadata.json"
            existing_meta: dict[str, Any] | None = None
            try:
                if meta_path.exists():
                    loaded = json.loads(meta_path.read_text(encoding="utf-8"))
                    if isinstance(loaded, dict):
                        existing_meta = loaded
                    else:
                        logger.warning(
                            "Repairing metadata sidecar with non-object payload: %s",
                            meta_path,
                        )
            except (json.JSONDecodeError, OSError) as exc:
                logger.warning("Repairing corrupt metadata: %s (%s)", meta_path, exc)

            stored_at = existing_meta.get("stored_at") if existing_meta else None
            canonical = self._metadata_from_snapshot(
                entry.snapshot_id,
                entry.snapshot,
                stored_at=stored_at if isinstance(stored_at, (int, float)) else None,
            )
            results.append(canonical)

            if existing_meta != canonical:
                try:
                    meta_path.write_text(json.dumps(canonical, indent=2), encoding="utf-8")
                except OSError as exc:
                    logger.warning("Failed to repair metadata sidecar %s (%s)", meta_path, exc)

        for meta_path in self.store_dir.glob("*/metadata.json"):
            if meta_path.parent.name not in spec_ids:
                logger.warning("Ignoring orphan metadata without spec.json: %s", meta_path)

        results.sort(key=lambda m: m.get("stored_at", 0), reverse=True)
        return results

    async def get(self, snapshot_id: str) -> SnapshotSpec:
        """Load a specific snapshot by ID.

        Raises:
            FileNotFoundError: If the snapshot does not exist.
        """
        spec_path = self.store_dir / snapshot_id / "spec.json"
        if not spec_path.exists():
            raise FileNotFoundError(f"Snapshot not found: {snapshot_id}")
        return self._load_spec(spec_path)

    async def get_entry(self, snapshot_id: str) -> StoredSnapshot:
        """Load a specific snapshot plus its ID."""
        return StoredSnapshot(
            snapshot_id=snapshot_id,
            snapshot=await self.get(snapshot_id),
        )

    @staticmethod
    def _metadata_from_snapshot(
        snapshot_id: str,
        snapshot: SnapshotSpec,
        *,
        stored_at: float | None = None,
    ) -> dict[str, Any]:
        return {
            "snapshot_id": snapshot_id,
            "vuln_classes": [v.type for v in snapshot.truth_graph.vulns],
            "golden_path_steps": len(snapshot.golden_path),
            "flag_count": len(snapshot.flags),
            "npc_count": len(snapshot.npc_personas),
            "has_compose": bool(snapshot.compose),
            "has_payload_files": bool(snapshot.files),
            "live_validated": bool(snapshot.topology.get("live_validated", False)),
            "parent_snapshot_id": snapshot.lineage.parent_snapshot_id,
            "root_snapshot_id": snapshot.lineage.root_snapshot_id,
            "generation_depth": snapshot.lineage.generation_depth,
            "mutation_summary": list(snapshot.lineage.mutation_summary),
            "stored_at": float(time.time() if stored_at is None else stored_at),
        }

    @staticmethod
    def _load_spec(spec_path: Path) -> SnapshotSpec:
        try:
            raw = json.loads(spec_path.read_text(encoding="utf-8"))
            return SnapshotSpec.model_validate(raw)
        except Exception as exc:  # noqa: BLE001
            raise ValueError(f"invalid snapshot spec at {spec_path}: {exc}") from exc