// 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.

#nullable disable

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using osu.Game.Rulesets;
using osu.Game.Rulesets.Objects;

namespace osu.Game.Beatmaps
{
    /// <summary>
    /// Converts a Beatmap for another mode.
    /// </summary>
    /// <typeparam name="T">The type of HitObject stored in the Beatmap.</typeparam>
    public abstract class BeatmapConverter<T> : IBeatmapConverter
        where T : HitObject
    {
        private event Action<HitObject, IEnumerable<HitObject>> objectConverted;

        event Action<HitObject, IEnumerable<HitObject>> IBeatmapConverter.ObjectConverted
        {
            add => objectConverted += value;
            remove => objectConverted -= value;
        }

        public IBeatmap Beatmap { get; }

        protected BeatmapConverter(IBeatmap beatmap, Ruleset ruleset)
        {
            Beatmap = beatmap;
        }

        /// <summary>
        /// Whether <see cref="Beatmap"/> can be converted by this <see cref="BeatmapConverter{T}"/>.
        /// </summary>
        public abstract bool CanConvert();

        public IBeatmap Convert(CancellationToken cancellationToken = default)
        {
            // We always operate on a clone of the original beatmap, to not modify it game-wide
            var original = Beatmap.Clone();

            // Shallow clone isn't enough to ensure we don't mutate beatmap info unexpectedly.
            // Can potentially be removed after `Beatmap.Difficulty` doesn't save back to `Beatmap.BeatmapInfo`.
            original.BeatmapInfo = original.BeatmapInfo.Clone();
            original.ControlPointInfo = original.ControlPointInfo.DeepClone();

            return ConvertBeatmap(original, cancellationToken);
        }

        /// <summary>
        /// Performs the conversion of a Beatmap using this Beatmap Converter.
        /// </summary>
        /// <param name="original">The un-converted Beatmap.</param>
        /// <param name="cancellationToken">The cancellation token.</param>
        /// <returns>The converted Beatmap.</returns>
        protected virtual Beatmap<T> ConvertBeatmap(IBeatmap original, CancellationToken cancellationToken)
        {
            var beatmap = CreateBeatmap();

            beatmap.BeatmapInfo = original.BeatmapInfo;
            beatmap.ControlPointInfo = original.ControlPointInfo;
            beatmap.HitObjects = convertHitObjects(original.HitObjects, original, cancellationToken).OrderBy(s => s.StartTime).ToList();
            beatmap.Breaks = original.Breaks;
            beatmap.UnhandledEventLines = original.UnhandledEventLines;

            return beatmap;
        }

        private List<T> convertHitObjects(IReadOnlyList<HitObject> hitObjects, IBeatmap beatmap, CancellationToken cancellationToken)
        {
            var result = new List<T>(hitObjects.Count);

            foreach (var obj in hitObjects)
            {
                if (obj is T tObj)
                {
                    result.Add(tObj);
                    continue;
                }

                var converted = ConvertHitObject(obj, beatmap, cancellationToken);

                if (objectConverted != null)
                {
                    converted = converted.ToList();
                    objectConverted.Invoke(obj, converted);
                }

                foreach (var c in converted)
                {
                    if (c != null)
                        result.Add(c);
                }
            }

            return result;
        }

        /// <summary>
        /// Creates the <see cref="Beatmap{T}"/> that will be returned by this <see cref="BeatmapProcessor"/>.
        /// </summary>
        protected virtual Beatmap<T> CreateBeatmap() => new Beatmap<T>();

        /// <summary>
        /// Performs the conversion of a hit object.
        /// This method is generally executed sequentially for all objects in a beatmap.
        /// </summary>
        /// <param name="original">The hit object to convert.</param>
        /// <param name="beatmap">The un-converted Beatmap.</param>
        /// <param name="cancellationToken">The cancellation token.</param>
        /// <returns>The converted hit object.</returns>
        protected virtual IEnumerable<T> ConvertHitObject(HitObject original, IBeatmap beatmap, CancellationToken cancellationToken) => Enumerable.Empty<T>();
    }
}