"""Local file cache for remote transcript files.

Provides transparent caching of remote files (e.g., S3) to local disk,
with multiprocess coordination via marker files.
"""

import atexit
import hashlib
import os
import shutil
import tempfile
from logging import getLogger
from pathlib import Path
from typing import Callable, Final

import anyio
from inspect_ai._util.asyncfiles import AsyncFilesystem
from inspect_ai._util.file import filesystem
from inspect_ai.util import trace_action, trace_message

logger = getLogger(__name__)


class LocalFilesCache:
    """Cache for remote files with automatic cleanup.

    Downloads remote files to a local temporary directory for faster access.
    Coordinates concurrent downloads across processes using marker files.
    """

    MAX_CACHE_FILE_SIZE: Final[int] = 5 * 1024 * 1024 * 1024  # 5GB

    def __init__(self, cache_dir: Path) -> None:
        """Initialize cache with specified directory.

        Args:
            cache_dir: Directory to store cached files. Created immediately.
        """
        self._cache_dir = cache_dir
        self._cache_dir.mkdir(parents=True, exist_ok=True)

    @property
    def cache_dir(self) -> Path:
        """Get the cache directory path."""
        return self._cache_dir

    async def resolve_remote_uri_to_local(self, fs: AsyncFilesystem, uri: str) -> str:
        """Resolve a URI to a local file path, downloading if necessary.

        If the URI is already local, returns it unchanged. If remote,
        downloads to cache (or waits for another process to finish downloading)
        and returns the cached file path.

        Args:
            fs: AsyncFilesystem instance for reading remote files.
            uri: File URI (local path or remote URL like s3://)

        Returns:
            Local file path that can be accessed directly.
        """
        if filesystem(uri).is_local():
            return uri

        # Check total cache size - skip caching if cache is full
        total_cache_size = sum(
            f.stat().st_size
            for f in self._cache_dir.iterdir()
            if f.is_file() and not f.suffix == ".downloading"
        )
        if total_cache_size > self.MAX_CACHE_FILE_SIZE:
            return uri

        # Generate unique cache filename from URI hash
        uri_hash = hashlib.sha256(uri.encode()).hexdigest()
        cache_file = self._cache_dir / uri_hash
        marker_file = cache_file.with_suffix(".downloading")

        while True:
            if cache_file.exists():
                return cache_file.as_posix()

            if not _try_create_marker(marker_file):
                trace_message(logger, "Scout Cache Wait", f"Waiting for {uri}")
                await anyio.sleep(1)
                continue

            # We own the marker now - download
            with trace_action(logger, "Scout Cache Download", f"Downloading {uri}"):
                try:
                    await _download_file(fs, uri, marker_file)
                    marker_file.rename(cache_file)
                    return cache_file.as_posix()
                except Exception:
                    marker_file.unlink(missing_ok=True)
                    raise

    def cleanup(self) -> None:
        """Delete the cache directory and all its contents."""
        if self._cache_dir.exists():
            shutil.rmtree(self._cache_dir)


async def _download_file(fs: AsyncFilesystem, uri: str, dest_path: Path) -> None:
    """Download remote file to local path."""
    await fs.get_file(uri, dest_path.as_posix())


def _try_create_marker(marker_file: Path) -> bool:
    """Atomically create marker file if it doesn't exist."""
    try:
        marker_fd = os.open(marker_file, os.O_CREAT | os.O_EXCL | os.O_WRONLY)
        os.close(marker_fd)
        return True
    except FileExistsError:
        return False


def create_temp_cache() -> LocalFilesCache:
    """Create a cache with a temporary directory.

    Returns:
        LocalFilesCache: Cache instance with temp directory.
    """
    temp_dir = tempfile.mkdtemp(prefix="inspect_scout_cache_")
    return LocalFilesCache(Path(temp_dir))


_task_files_cache: tuple[LocalFilesCache, int, Callable[[], None]] | None = None


def init_task_files_cache() -> LocalFilesCache:
    global _task_files_cache
    if not _task_files_cache:
        cache = create_temp_cache()
        handler = atexit.register(_atexit_task_files_cache)
        _task_files_cache = (cache, os.getpid(), handler)
    return _task_files_cache[0]


def _atexit_task_files_cache() -> None:
    if _task_files_cache and _task_files_cache[1] == os.getpid():
        cleanup_task_files_cache()


def cleanup_task_files_cache() -> None:
    global _task_files_cache
    if _task_files_cache:
        atexit.unregister(_task_files_cache[2])
        _task_files_cache[0].cleanup()
        _task_files_cache = None
