// 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.Linq;
using osu.Framework.Utils;
using osu.Game.Beatmaps;
using osu.Game.Replays;
using osu.Game.Rulesets.Catch.Beatmaps;
using osu.Game.Rulesets.Catch.Objects;
using osu.Game.Rulesets.Catch.UI;
using osu.Game.Rulesets.Replays;

namespace osu.Game.Rulesets.Catch.Replays
{
    internal class CatchAutoGenerator : AutoGenerator
    {
        public const double RELEASE_DELAY = 20;

        public new CatchBeatmap Beatmap => (CatchBeatmap)base.Beatmap;

        public CatchAutoGenerator(IBeatmap beatmap)
            : base(beatmap)
        {
            Replay = new Replay();
        }

        protected Replay Replay;

        private CatchReplayFrame currentFrame;

        public override Replay Generate()
        {
            if (Beatmap.HitObjects.Count == 0)
                return Replay;

            // todo: add support for HT DT
            const double dash_speed = Catcher.BASE_SPEED;
            const double movement_speed = dash_speed / 2;
            float lastPosition = CatchPlayfield.CENTER_X;
            double lastTime = 0;

            void moveToNext(PalpableCatchHitObject h)
            {
                float positionChange = Math.Abs(lastPosition - h.X);
                double timeAvailable = h.StartTime - lastTime;

                // So we can either make it there without a dash or not.
                // If positionChange is 0, we don't need to move, so speedRequired should also be 0 (could be NaN if timeAvailable is 0 too)
                // The case where positionChange > 0 and timeAvailable == 0 results in PositiveInfinity which provides expected beheaviour.
                double speedRequired = positionChange == 0 ? 0 : positionChange / timeAvailable;

                bool dashRequired = speedRequired > movement_speed;
                bool impossibleJump = speedRequired > movement_speed * 2;

                // todo: get correct catcher size, based on difficulty CS.
                const float catcher_width_half = CatcherArea.CATCHER_SIZE * 0.3f * 0.5f;

                if (lastPosition - catcher_width_half < h.X && lastPosition + catcher_width_half > h.X)
                {
                    // we are already in the correct range.
                    lastTime = h.StartTime;
                    addFrame(h.StartTime, lastPosition);
                    return;
                }

                if (impossibleJump)
                {
                    addFrame(h.StartTime, h.X);
                }
                else if (h.HyperDash)
                {
                    addFrame(h.StartTime - timeAvailable, lastPosition);
                    addFrame(h.StartTime, h.X);
                }
                else if (dashRequired)
                {
                    // we do a movement in two parts - the dash part then the normal part...
                    double timeAtNormalSpeed = positionChange / movement_speed;
                    double timeWeNeedToSave = timeAtNormalSpeed - timeAvailable;
                    double timeAtDashSpeed = timeWeNeedToSave / 2;

                    float midPosition = (float)Interpolation.Lerp(lastPosition, h.X, (float)timeAtDashSpeed / timeAvailable);

                    // dash movement
                    addFrame(h.StartTime - timeAvailable + 1, lastPosition, true);
                    addFrame(h.StartTime - timeAvailable + timeAtDashSpeed, midPosition);
                    addFrame(h.StartTime, h.X);
                }
                else
                {
                    double timeBefore = positionChange / movement_speed;

                    addFrame(h.StartTime - timeBefore, lastPosition);
                    addFrame(h.StartTime, h.X);
                }

                lastTime = h.StartTime;
                lastPosition = h.X;
            }

            foreach (var obj in Beatmap.HitObjects)
            {
                if (obj is PalpableCatchHitObject palpableObject)
                {
                    moveToNext(palpableObject);
                }

                foreach (var nestedObj in obj.NestedHitObjects.Cast<CatchHitObject>())
                {
                    if (nestedObj is PalpableCatchHitObject palpableNestedObject)
                    {
                        moveToNext(palpableNestedObject);
                    }
                }
            }

            return Replay;
        }

        private void addFrame(double time, float? position = null, bool dashing = false)
        {
            // todo: can be removed once FramedReplayInputHandler correctly handles rewinding before first frame.
            if (Replay.Frames.Count == 0)
                Replay.Frames.Add(new CatchReplayFrame(time - 1, position, false, null));

            var last = currentFrame;
            currentFrame = new CatchReplayFrame(time, position, dashing, last);
            Replay.Frames.Add(currentFrame);
        }
    }
}