// 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.Diagnostics;
using System.Linq;
using System.Threading.Tasks;
using osu.Framework.Extensions.ObjectExtensions;
using osu.Framework.Logging;
using osu.Framework.Platform;
using osu.Game.Database;
using osu.Game.Online.API;
using osu.Game.Rulesets.Objects;

namespace osu.Game.Beatmaps
{
    /// <summary>
    /// Handles all processing required to ensure a local beatmap is in a consistent state with any changes.
    /// </summary>
    public class BeatmapUpdater : IDisposable
    {
        private readonly IWorkingBeatmapCache workingBeatmapCache;
        private readonly BeatmapOnlineLookupQueue onlineLookupQueue;
        private readonly BeatmapDifficultyCache difficultyCache;

        public BeatmapUpdater(IWorkingBeatmapCache workingBeatmapCache, BeatmapDifficultyCache difficultyCache, IAPIProvider api, Storage storage)
        {
            this.workingBeatmapCache = workingBeatmapCache;
            this.difficultyCache = difficultyCache;

            onlineLookupQueue = new BeatmapOnlineLookupQueue(api, storage);
        }

        /// <summary>
        /// Queue a beatmap for background processing.
        /// </summary>
        public void Queue(Live<BeatmapSetInfo> beatmap)
        {
            Logger.Log($"Queueing change for local beatmap {beatmap}");
            Task.Factory.StartNew(() => beatmap.PerformRead(Process));
        }

        /// <summary>
        /// Run all processing on a beatmap immediately.
        /// </summary>
        public void Process(BeatmapSetInfo beatmapSet) => beatmapSet.Realm.Write(r =>
        {
            // Before we use below, we want to invalidate.
            workingBeatmapCache.Invalidate(beatmapSet);

            // TODO: this call currently uses the local `online.db` lookup.
            // We probably don't want this to happen after initial import (as the data may be stale).
            onlineLookupQueue.Update(beatmapSet);

            foreach (var beatmap in beatmapSet.Beatmaps)
            {
                difficultyCache.Invalidate(beatmap);

                var working = workingBeatmapCache.GetWorkingBeatmap(beatmap);
                var ruleset = working.BeatmapInfo.Ruleset.CreateInstance();

                Debug.Assert(ruleset != null);

                var calculator = ruleset.CreateDifficultyCalculator(working);

                beatmap.StarRating = calculator.Calculate().StarRating;
                beatmap.Length = calculateLength(working.Beatmap);
                beatmap.BPM = 60000 / working.Beatmap.GetMostCommonBeatLength();
            }

            // And invalidate again afterwards as re-fetching the most up-to-date database metadata will be required.
            workingBeatmapCache.Invalidate(beatmapSet);
        });

        private double calculateLength(IBeatmap b)
        {
            if (!b.HitObjects.Any())
                return 0;

            var lastObject = b.HitObjects.Last();

            //TODO: this isn't always correct (consider mania where a non-last object may last for longer than the last in the list).
            double endTime = lastObject.GetEndTime();
            double startTime = b.HitObjects.First().StartTime;

            return endTime - startTime;
        }

        #region Implementation of IDisposable

        public void Dispose()
        {
            if (onlineLookupQueue.IsNotNull())
                onlineLookupQueue.Dispose();
        }

        #endregion
    }
}