// 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 osu.Framework.Allocation;
using osu.Framework.Bindables;
using osu.Framework.Extensions.IEnumerableExtensions;
using osu.Framework.Graphics;
using osu.Game.Beatmaps;
using osu.Game.Online.API;
using osu.Game.Online.API.Requests;
using osu.Game.Rulesets;

namespace osu.Game.Screens.Select
{
    public class DifficultyRecommender : Component
    {
        [Resolved]
        private IAPIProvider api { get; set; }

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

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

        private readonly Dictionary<RulesetInfo, double> recommendedStarDifficulty = new Dictionary<RulesetInfo, double>();

        private int pendingAPIRequests;

        [BackgroundDependencyLoader]
        private void load()
        {
            calculateRecommendedDifficulties();
        }

        /// <summary>
        /// Find the recommended difficulty from a selection of available difficulties for the current local user.
        /// </summary>
        /// <remarks>
        /// This requires the user to be online for now.
        /// </remarks>
        /// <param name="beatmaps">A collection of beatmaps to select a difficulty from.</param>
        /// <returns>The recommended difficulty, or null if a recommendation could not be provided.</returns>
        public BeatmapInfo GetRecommendedBeatmap(IEnumerable<BeatmapInfo> beatmaps)
        {
            if (!recommendedStarDifficulty.ContainsKey(ruleset.Value))
            {
                calculateRecommendedDifficulties();
                return null;
            }

            return beatmaps.OrderBy(b =>
            {
                var difference = b.StarDifficulty - recommendedStarDifficulty[ruleset.Value];
                return difference >= 0 ? difference * 2 : difference * -1; // prefer easier over harder
            }).FirstOrDefault();
        }

        private void calculateRecommendedDifficulties()
        {
            if (pendingAPIRequests > 0)
                return;
            if (api.LocalUser.Value is GuestUser)
                return;

            rulesets.AvailableRulesets.ForEach(rulesetInfo =>
            {
                var req = new GetUserRequest(api.LocalUser.Value.Id, rulesetInfo);

                req.Success += result =>
                {
                    // algorithm taken from https://github.com/ppy/osu-web/blob/e6e2825516449e3d0f3f5e1852c6bdd3428c3437/app/Models/User.php#L1505
                    recommendedStarDifficulty[rulesetInfo] = Math.Pow((double)(result.Statistics.PP ?? 0), 0.4) * 0.195;
                    pendingAPIRequests--;
                };

                req.Failure += _ => pendingAPIRequests--;

                pendingAPIRequests++;
                api.Queue(req);
            });
        }
    }
}