using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using Jellyfin.Data.Enums;
using Jellyfin.Plugin.JRay.Models;
using Jellyfin.Plugin.JRay.Services;
using Jellyfin.Plugin.JRay.Services.Interfaces;
using MediaBrowser.Controller.Entities;
using MediaBrowser.Controller.Entities.TV;
using MediaBrowser.Controller.Library;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace Jellyfin.Plugin.JRay.Controllers;

/// <summary>
/// Lets a remote extraction worker discover which library items still need
/// to be processed.
/// </summary>
[ApiController]
[Route("Plugins/JRay/Tasks")]
[Authorize(Roles = "Administrator")]
public class TasksController : ControllerBase
{
    private const int DefaultLimit = 10;
    private const int MaxLimit = 100;

    private readonly ILibraryManager _libraryManager;
    private readonly ITruthDataService _truthDataService;
    private readonly IMediaPolicyStore _policyStore;

    /// <summary>
    /// Initializes a new instance of the <see cref="TasksController"/> class.
    /// </summary>
    /// <param name="libraryManager">The Jellyfin library manager.</param>
    /// <param name="truthDataService">The truth data service.</param>
    /// <param name="policyStore">The prioritise/ignore policy store.</param>
    public TasksController(ILibraryManager libraryManager, ITruthDataService truthDataService, IMediaPolicyStore policyStore)
    {
        _libraryManager = libraryManager;
        _truthDataService = truthDataService;
        _policyStore = policyStore;
    }

    /// <summary>
    /// Gets a random sample of movies/episodes that have no truth data yet.
    /// </summary>
    /// <param name="limit">The maximum number of items to return (default 10, max 100).</param>
    /// <returns>Up to <paramref name="limit"/> items with no truth data, in random order.</returns>
    [HttpGet("Pending")]
    [ProducesResponseType(StatusCodes.Status200OK)]
    public ActionResult<IEnumerable<PendingExtractionItem>> GetPending([FromQuery] int limit = DefaultLimit)
    {
        var effectiveLimit = Math.Clamp(limit, 1, MaxLimit);
        var rules = _policyStore.GetRules();

        var items = _libraryManager.GetItemList(new InternalItemsQuery
        {
            IncludeItemTypes = new[] { BaseItemKind.Movie, BaseItemKind.Episode },
            IsVirtualItem = false,
            Recursive = true,
        });

        // Keep only items that still need truth data, then apply the policy:
        // drop anything ignored, and order prioritised items ahead of the rest.
        // Randomise within each tier so the backlog still spreads across workers.
        var pending = items
            .Where(item => MediaFileExists(item) && !_truthDataService.HasTruth(item.Id, item.Path))
            .Select(item => new
            {
                Item = item,
                Action = PolicyResolver.Resolve(rules, item.Id, GetSeriesId(item), item.Genres)
            })
            .Where(x => x.Action != PolicyAction.Ignore)
            .OrderByDescending(x => x.Action == PolicyAction.Prioritise)
            .ThenBy(_ => Random.Shared.Next())
            .Take(effectiveLimit)
            .Select(x => new PendingExtractionItem
            {
                ItemId = x.Item.Id,
                Path = x.Item.Path,
                Name = x.Item.Name
            });

        return Ok(pending);
    }

    /// <summary>
    /// Gets the series id for an episode, or <see cref="Guid.Empty"/> for any
    /// other item type (so series rules only ever match episodes).
    /// </summary>
    /// <param name="item">The library item.</param>
    /// <returns>The owning series id, or empty.</returns>
    internal static Guid GetSeriesId(BaseItem item)
    {
        return item is Episode episode ? episode.SeriesId : Guid.Empty;
    }

    /// <summary>
    /// Determines whether an item's backing media still exists on disk.
    /// <para>
    /// A library item can outlive its file: deleting media from disk does not
    /// always purge the Jellyfin database entry, and such ghosts keep
    /// <c>IsVirtualItem == false</c>, so filtering on that flag alone is not
    /// enough. Without this check the pending endpoint hands stale paths/URLs to
    /// extraction workers, and — because a missing file can never gain truth
    /// data — those items stay pending forever.
    /// </para>
    /// Only local (file-protocol) items are stat-checked; remote/streamed items
    /// are assumed present so we never stat something off-box.
    /// </summary>
    /// <param name="item">The library item.</param>
    /// <returns><c>true</c> if the item has usable backing media; otherwise <c>false</c>.</returns>
    internal static bool MediaFileExists(BaseItem item)
    {
        if (string.IsNullOrEmpty(item.Path))
        {
            return false;
        }

        if (!item.IsFileProtocol)
        {
            return true;
        }

        // Path may point at a file or, for folder-based media, a directory.
        return System.IO.File.Exists(item.Path) || Directory.Exists(item.Path);
    }
}