using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using Jellyfin.Data.Enums;
using Jellyfin.Database.Implementations;
using Jellyfin.Database.Implementations.Entities;
using Jellyfin.Extensions;
using MediaBrowser.Controller.Configuration;
using MediaBrowser.Controller.Dto;
using MediaBrowser.Controller.Entities;
using MediaBrowser.Controller.Entities.Movies;
using MediaBrowser.Controller.Library;
using MediaBrowser.Controller.Persistence;
using MediaBrowser.Model.Configuration;
using Microsoft.EntityFrameworkCore;
using BaseItemDto = MediaBrowser.Controller.Entities.BaseItem;

namespace Emby.Server.Implementations.Library.SimilarItems;

/// <summary>
/// Provides similar items for movies and trailers using weighted scoring.
/// </summary>
public sealed class MovieSimilarItemsProvider : ILocalSimilarItemsProvider<Movie>, ILocalSimilarItemsProvider<Trailer>, IBatchLocalSimilarItemsProvider
{
    private const int GenreWeight = 10;
    private const int TagWeight = 5;
    private const int StudioWeight = 5;
    private const int DirectorWeight = 50;
    private const int ActorWeight = 15;

    private static readonly (ItemValueType Type, int Weight)[] _itemValueDimensions =
    [
        (ItemValueType.Genre, GenreWeight),
        (ItemValueType.Tags, TagWeight),
        (ItemValueType.Studios, StudioWeight)
    ];

    private static readonly (string[] PersonTypes, int Weight)[] _peopleDimensions =
    [
        ([nameof(PersonKind.Director)], DirectorWeight),
        ([nameof(PersonKind.Actor), nameof(PersonKind.GuestStar)], ActorWeight)
    ];

    private readonly IDbContextFactory<JellyfinDbContext> _dbProvider;
    private readonly IItemQueryHelpers _queryHelpers;
    private readonly IServerConfigurationManager _serverConfigurationManager;

    /// <summary>
    /// Initializes a new instance of the <see cref="MovieSimilarItemsProvider"/> class.
    /// </summary>
    /// <param name="dbProvider">The database context factory.</param>
    /// <param name="queryHelpers">The shared query helpers.</param>
    /// <param name="serverConfigurationManager">The server configuration manager.</param>
    public MovieSimilarItemsProvider(
        IDbContextFactory<JellyfinDbContext> dbProvider,
        IItemQueryHelpers queryHelpers,
        IServerConfigurationManager serverConfigurationManager)
    {
        _dbProvider = dbProvider;
        _queryHelpers = queryHelpers;
        _serverConfigurationManager = serverConfigurationManager;
    }

    /// <inheritdoc/>
    public string Name => "Local Genre/Tag";

    /// <inheritdoc/>
    public MetadataPluginType Type => MetadataPluginType.LocalSimilarityProvider;

    /// <inheritdoc/>
    public async Task<IReadOnlyList<BaseItemDto>> GetSimilarItemsAsync(Movie item, SimilarItemsQuery query, CancellationToken cancellationToken)
    {
        var results = await GetBatchSimilarItemsAsync([item], query).ConfigureAwait(false);
        return results.TryGetValue(item.Id, out var items) ? items : [];
    }

    /// <inheritdoc/>
    public async Task<IReadOnlyList<BaseItemDto>> GetSimilarItemsAsync(Trailer item, SimilarItemsQuery query, CancellationToken cancellationToken)
    {
        var results = await GetBatchSimilarItemsAsync([item], query).ConfigureAwait(false);
        return results.TryGetValue(item.Id, out var items) ? items : [];
    }

    bool ILocalSimilarItemsProvider.Supports(Type itemType)
        => typeof(Movie).IsAssignableFrom(itemType) || typeof(Trailer).IsAssignableFrom(itemType);

    Task<IReadOnlyList<BaseItem>> ILocalSimilarItemsProvider.GetSimilarItemsAsync(BaseItem item, SimilarItemsQuery query, CancellationToken cancellationToken)
        => item switch
        {
            Movie movie => GetSimilarItemsAsync(movie, query, cancellationToken),
            Trailer trailer => GetSimilarItemsAsync(trailer, query, cancellationToken),
            _ => throw new ArgumentException($"Unsupported item type {item.GetType()}", nameof(item))
        };

    /// <inheritdoc/>
    public Task<Dictionary<Guid, IReadOnlyList<BaseItemDto>>> GetBatchSimilarItemsAsync(
        IReadOnlyList<BaseItemDto> sourceItems,
        SimilarItemsQuery query)
    {
        var includeItemTypes = new List<BaseItemKind> { BaseItemKind.Movie };
        if (_serverConfigurationManager.Configuration.EnableExternalContentInSuggestions)
        {
            includeItemTypes.Add(BaseItemKind.Trailer);
            includeItemTypes.Add(BaseItemKind.LiveTvProgram);
        }

        var limit = query.Limit ?? 50;
        var dtoOptions = query.DtoOptions ?? new DtoOptions();

        using var context = _dbProvider.CreateDbContext();

        // Phase 1: Score all candidates per source item
        var sourceIds = sourceItems.Select(i => i.Id).ToList();
        var perSourceScores = ComputeBatchScores(sourceIds, context);

        var allCandidateIds = new HashSet<Guid>();
        foreach (var (_, scores) in perSourceScores)
        {
            allCandidateIds.UnionWith(
                scores.OrderByDescending(kvp => kvp.Value)
                    .Take(limit * 3)
                    .Select(kvp => kvp.Key));
        }

        var result = new Dictionary<Guid, IReadOnlyList<BaseItemDto>>();
        if (allCandidateIds.Count == 0)
        {
            return Task.FromResult(result);
        }

        // Phase 2: One access filter for all candidates
        var filter = new InternalItemsQuery(query.User)
        {
            IncludeItemTypes = [.. includeItemTypes],
            ExcludeItemIds = [.. query.ExcludeItemIds],
            DtoOptions = dtoOptions,
            EnableGroupByMetadataKey = true,
            EnableTotalRecordCount = false,
            IsMovie = true,
            IsPlayed = false
        };

        _queryHelpers.PrepareFilterQuery(filter);
        var baseQuery = _queryHelpers.PrepareItemQuery(context, filter);
        baseQuery = _queryHelpers.TranslateQuery(baseQuery, context, filter);

        var allCandidateIdsList = allCandidateIds.ToList();
        var accessibleItems = baseQuery
            .Where(e => allCandidateIdsList.Contains(e.Id))
            .Select(e => new { e.Id, e.PresentationUniqueKey })
            .ToList();

        // Phase 3: Pick top IDs per source, dedup by PresentationUniqueKey
        var allOrderedIds = new HashSet<Guid>();
        var perSourceOrderedIds = new Dictionary<Guid, List<Guid>>();

        foreach (var item in sourceItems)
        {
            if (!perSourceScores.TryGetValue(item.Id, out var scores))
            {
                continue;
            }

            var orderedIds = accessibleItems
                .Where(x => scores.ContainsKey(x.Id))
                .OrderByDescending(x => scores.GetValueOrDefault(x.Id))
                .DistinctBy(x => x.PresentationUniqueKey)
                .Take(limit)
                .Select(x => x.Id)
                .ToList();

            if (orderedIds.Count > 0)
            {
                perSourceOrderedIds[item.Id] = orderedIds;
                allOrderedIds.UnionWith(orderedIds);
            }
        }

        if (allOrderedIds.Count == 0)
        {
            return Task.FromResult(result);
        }

        // Phase 4: One entity load for all results
        var allOrderedIdsList = allOrderedIds.ToList();
        var entitiesById = _queryHelpers.ApplyNavigations(
                context.BaseItems.AsNoTracking().Where(e => allOrderedIdsList.Contains(e.Id)),
                filter)
            .AsEnumerable()
            .Select(e => _queryHelpers.DeserializeBaseItem(e, filter.SkipDeserialization))
            .Where(dto => dto is not null)
            .ToDictionary(i => i!.Id);

        // Phase 5: Split by source, preserving score order
        foreach (var (sourceId, orderedIds) in perSourceOrderedIds)
        {
            var items = orderedIds
                .Where(entitiesById.ContainsKey)
                .Select(id => entitiesById[id]!)
                .ToList();

            if (items.Count > 0)
            {
                result[sourceId] = items;
            }
        }

        return Task.FromResult(result);
    }

    private Dictionary<Guid, Dictionary<Guid, int>> ComputeBatchScores(List<Guid> sourceIds, JellyfinDbContext context)
    {
        var result = new Dictionary<Guid, Dictionary<Guid, int>>();
        foreach (var id in sourceIds)
        {
            result[id] = [];
        }

        // Score item-value dimensions (genre, tags, studios)
        foreach (var (valueType, weight) in _itemValueDimensions)
        {
            var sourceMap = context.ItemValuesMap.AsNoTracking()
                .Where(m => sourceIds.Contains(m.ItemId) && m.ItemValue.Type == valueType)
                .Select(m => new { m.ItemId, m.ItemValue.CleanValue })
                .ToList()
                .GroupBy(m => m.ItemId)
                .ToDictionary(g => g.Key, g => g.Select(x => x.CleanValue).ToHashSet());

            var allValues = sourceMap.Values.SelectMany(v => v).Distinct().ToList();
            if (allValues.Count == 0)
            {
                continue;
            }

            var valueToCandidates = context.ItemValuesMap.AsNoTracking()
                .Where(m => m.ItemValue.Type == valueType && allValues.Contains(m.ItemValue.CleanValue))
                .Select(m => new { m.ItemId, m.ItemValue.CleanValue })
                .ToList()
                .GroupBy(m => m.CleanValue)
                .ToDictionary(g => g.Key, g => g.Select(x => x.ItemId).ToList());

            foreach (var sourceId in sourceIds)
            {
                if (!sourceMap.TryGetValue(sourceId, out var sourceValues))
                {
                    continue;
                }

                var scoreMap = result[sourceId];
                foreach (var value in sourceValues)
                {
                    if (valueToCandidates.TryGetValue(value, out var candidates))
                    {
                        foreach (var candidateId in candidates)
                        {
                            scoreMap[candidateId] = scoreMap.GetValueOrDefault(candidateId) + weight;
                        }
                    }
                }
            }
        }

        // Score people dimensions (directors, actors)
        foreach (var (personTypes, weight) in _peopleDimensions)
        {
            var sourceMap = context.PeopleBaseItemMap.AsNoTracking()
                .Where(m => sourceIds.Contains(m.ItemId) && personTypes.Contains(m.People.PersonType))
                .Select(m => new { m.ItemId, m.PeopleId })
                .ToList()
                .GroupBy(m => m.ItemId)
                .ToDictionary(g => g.Key, g => g.Select(x => x.PeopleId).ToHashSet());

            var allPeopleIds = sourceMap.Values.SelectMany(v => v).Distinct().ToList();
            if (allPeopleIds.Count == 0)
            {
                continue;
            }

            var personToCandidates = context.PeopleBaseItemMap.AsNoTracking()
                .Where(m => allPeopleIds.Contains(m.PeopleId))
                .Select(m => new { m.ItemId, m.PeopleId })
                .ToList()
                .GroupBy(m => m.PeopleId)
                .ToDictionary(g => g.Key, g => g.Select(x => x.ItemId).ToList());

            foreach (var sourceId in sourceIds)
            {
                if (!sourceMap.TryGetValue(sourceId, out var sourcePeopleIds))
                {
                    continue;
                }

                var scoreMap = result[sourceId];
                foreach (var peopleId in sourcePeopleIds)
                {
                    if (personToCandidates.TryGetValue(peopleId, out var candidates))
                    {
                        foreach (var candidateId in candidates)
                        {
                            scoreMap[candidateId] = scoreMap.GetValueOrDefault(candidateId) + weight;
                        }
                    }
                }
            }
        }

        // Remove self-references and empty entries
        foreach (var sourceId in sourceIds)
        {
            var scoreMap = result[sourceId];
            scoreMap.Remove(sourceId);
            if (scoreMap.Count == 0)
            {
                result.Remove(sourceId);
            }
        }

        return result;
    }
}