"""SHA-256 content cache for skipping unchanged docs on re-sync.

Stores one .sha256 file per doc in .discourse_sync_cache/. On re-run,
compares the current file hash against the cached hash to determine
whether the doc needs syncing.
"""

from __future__ import annotations

import hashlib
from pathlib import Path

DEFAULT_CACHE_DIR = Path(__file__).resolve().parent.parent.parent / ".discourse_sync_cache"


class ContentCache:
    """File-based SHA-256 content cache."""

    def __init__(self, cache_dir: str | Path = DEFAULT_CACHE_DIR) -> None:
        self._cache_dir = Path(cache_dir)

    @property
    def cache_dir(self) -> Path:
        return self._cache_dir

    @staticmethod
    def compute_hash(content: str) -> str:
        """Compute SHA-256 hex digest of content."""
        return hashlib.sha256(content.encode("utf-8")).hexdigest()

    def _cache_path(self, doc_path: str) -> Path:
        """Map a doc path (e.g. 'features/cruise/icbm.md') to its cache file."""
        slug = doc_path.replace("/", "_").replace(".md", "")
        return self._cache_dir / f"{slug}.sha256"

    def is_changed(self, doc_path: str, content: str) -> bool:
        """Return True if content differs from the cached hash (or no cache exists)."""
        content_hash = self.compute_hash(content)
        cached = self._cache_path(doc_path)
        if not cached.exists():
            return True
        return cached.read_text().strip() != content_hash

    def save(self, doc_path: str, content: str) -> None:
        """Save the SHA-256 hash of content to the cache file."""
        content_hash = self.compute_hash(content)
        self._cache_dir.mkdir(parents=True, exist_ok=True)
        self._cache_path(doc_path).write_text(content_hash + "\n")

    def clear(self) -> int:
        """Remove all cached hashes. Returns the number of files removed."""
        if not self._cache_dir.exists():
            return 0
        count = 0
        for f in self._cache_dir.glob("*.sha256"):
            f.unlink()
            count += 1
        return count