// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
// See the LICENCE file in the repository root for full licence text.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using osu.Framework.Allocation;
using osu.Framework.Bindables;
using osu.Framework.Extensions;
using osu.Game.Beatmaps;
using osu.Game.Database;
using osu.Game.Extensions;
using osu.Game.Online.API;
using osu.Game.Online.API.Requests;
using osu.Game.Online.Leaderboards;
using osu.Game.Rulesets;
using osu.Game.Rulesets.Mods;
using osu.Game.Scoring;
using Realms;

namespace osu.Game.Screens.Select.Leaderboards
{
    public class BeatmapLeaderboard : Leaderboard<BeatmapLeaderboardScope, ScoreInfo>
    {
        public Action<ScoreInfo> ScoreSelected;

        private BeatmapInfo beatmapInfo;

        public BeatmapInfo BeatmapInfo
        {
            get => beatmapInfo;
            set
            {
                if (beatmapInfo == null && value == null)
                    return;

                if (beatmapInfo?.Equals(value) == true)
                    return;

                beatmapInfo = value;
                RefetchScores();
            }
        }

        private bool filterMods;

        /// <summary>
        /// Whether to apply the game's currently selected mods as a filter when retrieving scores.
        /// </summary>
        public bool FilterMods
        {
            get => filterMods;
            set
            {
                if (value == filterMods)
                    return;

                filterMods = value;

                RefetchScores();
            }
        }

        [Resolved]
        private ScoreManager scoreManager { get; set; }

        [Resolved]
        private IBindable<RulesetInfo> ruleset { get; set; }

        [Resolved]
        private IBindable<IReadOnlyList<Mod>> mods { get; set; }

        [Resolved]
        private IAPIProvider api { get; set; }

        [Resolved]
        private RulesetStore rulesets { get; set; }

        [Resolved]
        private RealmAccess realm { get; set; }

        private IDisposable scoreSubscription;

        [BackgroundDependencyLoader]
        private void load()
        {
            ruleset.ValueChanged += _ => RefetchScores();
            mods.ValueChanged += _ =>
            {
                if (filterMods)
                    RefetchScores();
            };
        }

        protected override bool IsOnlineScope => Scope != BeatmapLeaderboardScope.Local;

        protected override APIRequest FetchScores(CancellationToken cancellationToken)
        {
            var fetchBeatmapInfo = BeatmapInfo;
            var fetchRuleset = ruleset.Value ?? fetchBeatmapInfo.Ruleset;

            if (fetchBeatmapInfo == null)
            {
                SetErrorState(LeaderboardState.NoneSelected);
                return null;
            }

            if (Scope == BeatmapLeaderboardScope.Local)
            {
                subscribeToLocalScores(cancellationToken);
                return null;
            }

            if (api?.IsLoggedIn != true)
            {
                SetErrorState(LeaderboardState.NotLoggedIn);
                return null;
            }

            if (!fetchRuleset.IsLegacyRuleset())
            {
                SetErrorState(LeaderboardState.RulesetUnavailable);
                return null;
            }

            if (fetchBeatmapInfo.OnlineID <= 0 || fetchBeatmapInfo.Status <= BeatmapOnlineStatus.Pending)
            {
                SetErrorState(LeaderboardState.BeatmapUnavailable);
                return null;
            }

            if (!api.LocalUser.Value.IsSupporter && (Scope != BeatmapLeaderboardScope.Global || filterMods))
            {
                SetErrorState(LeaderboardState.NotSupporter);
                return null;
            }

            IReadOnlyList<Mod> requestMods = null;

            if (filterMods && !mods.Value.Any())
                // add nomod for the request
                requestMods = new Mod[] { new ModNoMod() };
            else if (filterMods)
                requestMods = mods.Value;

            var req = new GetScoresRequest(fetchBeatmapInfo, fetchRuleset, Scope, requestMods);

            req.Success += r =>
            {
                scoreManager.OrderByTotalScoreAsync(r.Scores.Select(s => s.CreateScoreInfo(rulesets, fetchBeatmapInfo)).ToArray(), cancellationToken)
                            .ContinueWith(task => Schedule(() =>
                            {
                                if (cancellationToken.IsCancellationRequested)
                                    return;

                                SetScores(task.GetResultSafely(), r.UserScore?.CreateScoreInfo(rulesets, fetchBeatmapInfo));
                            }), TaskContinuationOptions.OnlyOnRanToCompletion);
            };

            return req;
        }

        protected override LeaderboardScore CreateDrawableScore(ScoreInfo model, int index) => new LeaderboardScore(model, index, IsOnlineScope)
        {
            Action = () => ScoreSelected?.Invoke(model)
        };

        protected override LeaderboardScore CreateDrawableTopScore(ScoreInfo model) => new LeaderboardScore(model, model.Position, false)
        {
            Action = () => ScoreSelected?.Invoke(model)
        };

        private void subscribeToLocalScores(CancellationToken cancellationToken)
        {
            scoreSubscription?.Dispose();
            scoreSubscription = null;

            if (beatmapInfo == null)
                return;

            scoreSubscription = realm.RegisterForNotifications(r =>
                r.All<ScoreInfo>().Filter($"{nameof(ScoreInfo.BeatmapInfo)}.{nameof(BeatmapInfo.ID)} == $0"
                                          + $" AND {nameof(ScoreInfo.Ruleset)}.{nameof(RulesetInfo.ShortName)} == $1"
                                          + $" AND {nameof(ScoreInfo.DeletePending)} == false"
                    , beatmapInfo.ID, ruleset.Value.ShortName), localScoresChanged);

            void localScoresChanged(IRealmCollection<ScoreInfo> sender, ChangeSet changes, Exception exception)
            {
                if (cancellationToken.IsCancellationRequested)
                    return;

                // This subscription may fire from changes to linked beatmaps, which we don't care about.
                // It's currently not possible for a score to be modified after insertion, so we can safely ignore callbacks with only modifications.
                if (changes?.HasCollectionChanges() == false)
                    return;

                var scores = sender.AsEnumerable();

                if (filterMods && !mods.Value.Any())
                {
                    // we need to filter out all scores that have any mods to get all local nomod scores
                    scores = scores.Where(s => !s.Mods.Any());
                }
                else if (filterMods)
                {
                    // otherwise find all the scores that have *any* of the currently selected mods (similar to how web applies mod filters)
                    // we're creating and using a string list representation of selected mods so that it can be translated into the DB query itself
                    var selectedMods = mods.Value.Select(m => m.Acronym);
                    scores = scores.Where(s => s.Mods.Any(m => selectedMods.Contains(m.Acronym)));
                }

                scores = scores.Detach();

                scoreManager.OrderByTotalScoreAsync(scores.ToArray(), cancellationToken)
                            .ContinueWith(ordered => Schedule(() =>
                            {
                                if (cancellationToken.IsCancellationRequested)
                                    return;

                                SetScores(ordered.GetResultSafely());
                            }), TaskContinuationOptions.OnlyOnRanToCompletion);
            }
        }

        protected override void Dispose(bool isDisposing)
        {
            base.Dispose(isDisposing);
            scoreSubscription?.Dispose();
        }
    }
}