"""Bounded, generation-safe media downloading and canonical slot cleanup."""

from __future__ import annotations

import logging
import os
import signal
import shutil
import subprocess
import threading
import time
import uuid
from concurrent.futures import Future, ThreadPoolExecutor
from dataclasses import dataclass
from pathlib import Path
from typing import Any, Callable

from .config import ControllerConfig
from .contracts import SLOT_IDS
from .models import DeleteToken, DownloadReservation, SlotProtectedError, StaleOperationError
from .store import ControllerStore


LOG = logging.getLogger(__name__)
MEDIA_EXTENSIONS = frozenset({".mp4", ".mkv", ".webm", ".mov", ".m4v"})


@dataclass(frozen=True)
class DownloadEvent:
    slot: int
    state: str
    title: str | None = None
    count: int | None = None
    message: str | None = None
    job_id: str | None = None
    generation: int | None = None
    url: str | None = None
    submitter: str | None = None
    note: str | None = None
    reused_slot: bool = False


EventCallback = Callable[[DownloadEvent], None]
Runner = Callable[..., subprocess.CompletedProcess[str]]


def canonical_slot_directory(media_base: Path, slot: int) -> Path:
    if slot not in SLOT_IDS:
        raise ValueError(f"slot must be in 1..10, got {slot!r}")
    return media_base / f"slot{slot}"


def canonical_playlist_path(media_base: Path, slot: int) -> Path:
    return canonical_slot_directory(media_base, slot) / "playlist.m3u"


def title_from_filename(path: Path) -> str:
    stem = path.stem
    if " - " in stem:
        stem = stem.split(" - ", 1)[1]
    if " [" in stem:
        stem = stem.rsplit(" [", 1)[0]
    return stem


class DownloadManager:
    """Reserve synchronously, then perform work on a bounded executor."""

    def __init__(
        self,
        config: ControllerConfig,
        store: ControllerStore,
        *,
        on_event: EventCallback | None = None,
        runner: Runner | None = None,
        executor: ThreadPoolExecutor | None = None,
    ):
        self.config = config
        self.store = store
        self.on_event = on_event or (lambda event: None)
        self.runner = runner
        self._executor = executor or ThreadPoolExecutor(
            max_workers=config.downloads.max_workers,
            thread_name_prefix="yt-download",
        )
        self._owns_executor = executor is None
        self._lock = threading.Lock()
        self._futures: set[Future[Any]] = set()
        self._processes: set[subprocess.Popen[str]] = set()
        self._stopping = False

    def enqueue(
        self,
        url: str,
        submitter: str | None,
        note: str | None,
    ) -> DownloadReservation:
        with self._lock:
            if self._stopping:
                return DownloadReservation(status="shutting_down")
        reservation = self.store.reserve_download(url, submitter, note)
        if reservation.status != "reserved":
            return reservation
        assert reservation.slot is not None
        assert reservation.job_id is not None
        assert reservation.generation is not None

        # Publish/record queued after the transaction commits and before a
        # worker can publish downloading or ready.
        self._emit(
            DownloadEvent(
                slot=reservation.slot,
                state="queued",
                job_id=reservation.job_id,
                generation=reservation.generation,
                url=url,
                submitter=submitter,
                note=note,
                reused_slot=reservation.reused_slot,
            )
        )
        try:
            future = self._executor.submit(
                self._download,
                url,
                reservation.slot,
                reservation.generation,
                reservation.job_id,
            )
        except BaseException as exc:
            message = f"could not start download worker: {exc}"
            self.store.fail_download(
                reservation.job_id,
                reservation.slot,
                reservation.generation,
                message,
            )
            self._emit(
                DownloadEvent(
                    slot=reservation.slot,
                    state="error",
                    message=message,
                    job_id=reservation.job_id,
                    generation=reservation.generation,
                )
            )
            return DownloadReservation(
                status="worker_error",
                slot=reservation.slot,
                generation=reservation.generation,
                job_id=reservation.job_id,
                reused_slot=reservation.reused_slot,
            )

        with self._lock:
            self._futures.add(future)
        future.add_done_callback(self._forget_future)
        return reservation

    def _forget_future(self, future: Future[Any]) -> None:
        with self._lock:
            self._futures.discard(future)
        try:
            future.result()
        except BaseException:
            LOG.exception("download worker escaped its failure boundary")

    def _emit(self, event: DownloadEvent) -> None:
        try:
            self.on_event(event)
        except BaseException:
            LOG.exception("download event callback failed")

    def _cookie_arguments(self) -> list[str]:
        path = self.config.downloads.cookie_path
        if path is None:
            return []
        if path.is_file():
            return ["--cookies", str(path)]
        if self.config.downloads.cookie_required:
            raise FileNotFoundError(f"required yt-dlp cookie file is missing: {path}")
        LOG.warning("yt-dlp cookie file is unavailable; continuing without it: %s", path)
        return []

    def _base_yt_dlp_arguments(self) -> list[str]:
        return [self.config.downloads.yt_dlp_binary, "--ignore-config"] + self._cookie_arguments()

    def _get_title(self, url: str) -> tuple[str, str | None]:
        arguments = self._base_yt_dlp_arguments() + [
            "--flat-playlist",
            "--print",
            "%(playlist_title)s|||%(title)s|||%(id)s",
            "--playlist-end",
            "1",
            url,
        ]
        try:
            result = self._run_command(
                arguments,
                check=True,
                capture_output=True,
                text=True,
                timeout=min(120.0, self.config.downloads.process_timeout_seconds),
            )
            line = (result.stdout or "").strip().splitlines()[0]
            playlist_title, _, remainder = line.partition("|||")
            video_title, _, yt_id = remainder.partition("|||")
            playlist_title = playlist_title.strip()
            video_title = video_title.strip()
            title = (
                playlist_title
                if playlist_title and playlist_title.upper() not in {"NA", "NONE"}
                else video_title
            )
            return title or url, yt_id.strip() or None
        except (IndexError, OSError, subprocess.SubprocessError, ValueError) as exc:
            LOG.warning("could not determine media title for %s: %s", url, exc)
            return url, None

    def _download(
        self,
        url: str,
        slot: int,
        generation: int,
        job_id: str,
    ) -> None:
        if not self.store.mark_download_running(job_id, slot, generation):
            return
        self._emit(
            DownloadEvent(
                slot=slot,
                state="downloading",
                job_id=job_id,
                generation=generation,
            )
        )
        slot_directory = canonical_slot_directory(self.config.storage.media_base, slot)
        temporary_playlist = slot_directory / f".playlist.{job_id}.tmp"
        try:
            slot_directory.mkdir(parents=True, exist_ok=True)
            if slot_directory.is_symlink():
                raise RuntimeError(f"refusing to download through symlink: {slot_directory}")
            title, yt_id = self._get_title(url)
            arguments = self._base_yt_dlp_arguments() + [
                "--yes-playlist",
                "--no-overwrites",
                "--no-progress",
                "-o",
                str(
                    slot_directory
                    / "%(playlist_index)03d - %(title)s [%(id)s].%(ext)s"
                ),
                "-f",
                (
                    f"bv*[height<={self.config.downloads.max_height}]+ba/"
                    f"b[height<={self.config.downloads.max_height}]/b"
                ),
                url,
            ]
            self._run_command(
                arguments,
                check=True,
                text=True,
                timeout=self.config.downloads.process_timeout_seconds,
            )
            media_files = sorted(
                path
                for path in slot_directory.iterdir()
                if path.is_file() and path.suffix.lower() in MEDIA_EXTENSIONS
            )
            if not media_files:
                raise RuntimeError("yt-dlp completed without producing media files")

            items = [
                (title_from_filename(path), os.path.relpath(path, slot_directory))
                for path in media_files
            ]
            with temporary_playlist.open("w", encoding="utf-8", newline="\n") as stream:
                for _, relative_path in items:
                    stream.write(relative_path + "\n")
                stream.flush()
                os.fsync(stream.fileno())
            os.replace(
                temporary_playlist,
                canonical_playlist_path(self.config.storage.media_base, slot),
            )
            self._fsync_directory(slot_directory)

            if not self.store.complete_download(
                job_id,
                slot,
                generation,
                title=title,
                items=items,
                yt_id=yt_id,
            ):
                LOG.warning(
                    "ignored stale download completion job=%s slot=%s generation=%s",
                    job_id,
                    slot,
                    generation,
                )
                return
            self._emit(
                DownloadEvent(
                    slot=slot,
                    state="ready",
                    title=title,
                    count=len(items),
                    job_id=job_id,
                    generation=generation,
                )
            )
        except BaseException as exc:
            temporary_playlist.unlink(missing_ok=True)
            message = self._failure_message(exc)
            self.store.fail_download(job_id, slot, generation, message)
            self._emit(
                DownloadEvent(
                    slot=slot,
                    state="error",
                    message=message,
                    job_id=job_id,
                    generation=generation,
                )
            )

    @staticmethod
    def _failure_message(exc: BaseException) -> str:
        if isinstance(exc, subprocess.TimeoutExpired):
            return f"yt-dlp timed out after {exc.timeout} seconds"
        if isinstance(exc, subprocess.CalledProcessError):
            return f"yt-dlp failed with exit code {exc.returncode}"
        return f"download failed: {exc}"

    def _run_command(
        self,
        arguments: list[str],
        *,
        check: bool,
        text: bool,
        timeout: float,
        capture_output: bool = False,
    ) -> subprocess.CompletedProcess[str]:
        if self.runner is not None:
            return self.runner(
                arguments,
                check=check,
                text=text,
                timeout=timeout,
                capture_output=capture_output,
            )

        with self._lock:
            if self._stopping:
                raise RuntimeError("Controller is shutting down")
            process = subprocess.Popen(
                arguments,
                stdout=subprocess.PIPE if capture_output else None,
                stderr=subprocess.PIPE if capture_output else None,
                text=text,
                start_new_session=True,
            )
            self._processes.add(process)
        try:
            try:
                stdout, stderr = process.communicate(timeout=timeout)
            except subprocess.TimeoutExpired:
                self._terminate_process(process, force=False)
                try:
                    stdout, stderr = process.communicate(timeout=2.0)
                except subprocess.TimeoutExpired:
                    self._terminate_process(process, force=True)
                    stdout, stderr = process.communicate()
                raise subprocess.TimeoutExpired(
                    arguments,
                    timeout,
                    output=stdout,
                    stderr=stderr,
                )
            completed = subprocess.CompletedProcess(
                arguments,
                process.returncode,
                stdout=stdout,
                stderr=stderr,
            )
            if check and process.returncode:
                raise subprocess.CalledProcessError(
                    process.returncode,
                    arguments,
                    output=stdout,
                    stderr=stderr,
                )
            return completed
        finally:
            with self._lock:
                self._processes.discard(process)

    @staticmethod
    def _terminate_process(
        process: subprocess.Popen[str],
        *,
        force: bool,
    ) -> None:
        if process.poll() is not None:
            return
        try:
            os.killpg(
                process.pid,
                signal.SIGKILL if force else signal.SIGTERM,
            )
        except ProcessLookupError:
            return
        except OSError:
            try:
                process.kill() if force else process.terminate()
            except ProcessLookupError:
                pass

    @staticmethod
    def _fsync_directory(path: Path) -> None:
        descriptor = os.open(path, os.O_RDONLY | getattr(os, "O_DIRECTORY", 0))
        try:
            os.fsync(descriptor)
        finally:
            os.close(descriptor)

    def delete_slot(
        self,
        slot: int,
        *,
        reason: str,
        expected_url: str | None = None,
    ) -> bool:
        token = self.store.begin_delete(slot, reason=reason, expected_url=expected_url)
        return self.finish_deletion(token)

    def finish_deletion(self, token: DeleteToken) -> bool:
        slot_directory = canonical_slot_directory(self.config.storage.media_base, token.slot)
        trash_root = self.config.storage.media_base / ".controller-trash"
        trash_path: Path | None = None
        if os.path.lexists(slot_directory):
            if slot_directory.is_symlink():
                slot_directory.unlink()
            else:
                trash_root.mkdir(parents=True, exist_ok=True)
                trash_path = trash_root / (
                    f"slot{token.slot}.generation{token.generation}.{uuid.uuid4().hex}"
                )
                os.replace(slot_directory, trash_path)
                self._fsync_directory(self.config.storage.media_base)
        if trash_path is not None:
            shutil.rmtree(trash_path)
        return self.store.finish_delete(token)

    def expire_due_slots(self) -> list[int]:
        deleted: list[int] = []
        for token in self.store.begin_expired_deletions():
            try:
                if self.finish_deletion(token):
                    deleted.append(token.slot)
            except OSError:
                LOG.exception("could not finish expired deletion for slot %s", token.slot)
        return deleted

    def recover_pending_deletions(self) -> list[int]:
        recovered: list[int] = []
        trash_root = self.config.storage.media_base / ".controller-trash"
        for token in self.store.pending_deletions():
            if trash_root.is_dir():
                prefix = f"slot{token.slot}.generation{token.generation}."
                for candidate in trash_root.iterdir():
                    if candidate.name.startswith(prefix):
                        if candidate.is_symlink() or candidate.is_file():
                            candidate.unlink()
                        elif candidate.is_dir():
                            shutil.rmtree(candidate)
            if self.finish_deletion(token):
                recovered.append(token.slot)
        return recovered

    def shutdown(self, *, wait: bool = True) -> None:
        with self._lock:
            self._stopping = True
            processes = tuple(self._processes)
        for process in processes:
            self._terminate_process(process, force=False)
        deadline = time.monotonic() + 2.0
        for process in processes:
            if process.poll() is not None:
                continue
            try:
                process.wait(timeout=max(0.0, deadline - time.monotonic()))
            except subprocess.TimeoutExpired:
                self._terminate_process(process, force=True)
        if self._owns_executor:
            self._executor.shutdown(wait=wait, cancel_futures=True)

    def active_future_count(self) -> int:
        with self._lock:
            return len(self._futures)