using System;
using UnityEngine;

namespace AibisDream.FrameAnimation
{
    internal readonly struct FrameAnimationSessionEvaluation
    {
        public static FrameAnimationSessionEvaluation Running =>
            new FrameAnimationSessionEvaluation(
                false,
                FrameClipEndBehavior.HoldLastFrame,
                FrameAnimationPlaybackError.None);

        public bool IsCompleted { get; }
        public FrameClipEndBehavior EndBehavior { get; }
        public FrameAnimationPlaybackError Error { get; }
        public bool IsFailed => Error.Code != FrameAnimationPlaybackErrorCode.None;

        private FrameAnimationSessionEvaluation(
            bool isCompleted,
            FrameClipEndBehavior endBehavior,
            FrameAnimationPlaybackError error)
        {
            IsCompleted = isCompleted;
            EndBehavior = endBehavior;
            Error = error;
        }

        public static FrameAnimationSessionEvaluation Completed(FrameClipEndBehavior endBehavior)
        {
            return new FrameAnimationSessionEvaluation(true, endBehavior, FrameAnimationPlaybackError.None);
        }

        public static FrameAnimationSessionEvaluation Failed(
            FrameAnimationPlaybackErrorCode code,
            string message)
        {
            return new FrameAnimationSessionEvaluation(
                false,
                FrameClipEndBehavior.HoldLastFrame,
                new FrameAnimationPlaybackError(code, message));
        }
    }

    internal sealed class FrameAnimationPlaybackSession
    {
        private const double Epsilon = 0.000000001d;

        private readonly ResolvedPlaybackPlan plan;
        private int stepIndex;
        private int frameIndex;
        private double frameElapsedSeconds;
        private bool hasStarted;
        private bool hasCompleted;

        public string PlayableId => plan.PlayableId;
        public string CurrentClipId => CurrentStep?.Clip != null ? CurrentStep.Clip.Id : string.Empty;
        public string CurrentNodeId => plan.IsFlow && CurrentStep != null ? CurrentStep.NodeId : string.Empty;
        public int CurrentFrameIndex => hasStarted && !hasCompleted ? frameIndex : -1;
        public FrameClip CurrentClip => CurrentStep?.Clip;

        private ResolvedPlaybackStep CurrentStep =>
            stepIndex >= 0 && stepIndex < plan.Steps.Count ? plan.Steps[stepIndex] : null;

        internal FrameAnimationPlaybackSession(ResolvedPlaybackPlan plan)
        {
            this.plan = plan ?? throw new ArgumentNullException(nameof(plan));
        }

        public void Start(Action<Sprite> applySprite)
        {
            if (hasStarted)
            {
                return;
            }

            hasStarted = true;
            stepIndex = 0;
            frameIndex = 0;
            frameElapsedSeconds = 0d;
            ApplyCurrentFrame(applySprite);
        }

        public FrameAnimationSessionEvaluation Evaluate(
            double deltaTimeSeconds,
            float playerSpeed,
            Action<Sprite> applySprite)
        {
            if (!hasStarted || hasCompleted || deltaTimeSeconds <= 0d)
            {
                return FrameAnimationSessionEvaluation.Running;
            }

            var remainingRealSeconds = deltaTimeSeconds;
            while (remainingRealSeconds > Epsilon)
            {
                var step = CurrentStep;
                if (step?.Clip == null ||
                    frameIndex < 0 ||
                    frameIndex >= step.Clip.FrameCount)
                {
                    hasCompleted = true;
                    return FrameAnimationSessionEvaluation.Failed(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        "播放期间 Clip 或 Frame 数据失效。");
                }

                var effectiveSpeed = playerSpeed * step.PlaybackSpeed;
                if (!FrameAnimationValueUtility.IsValidSpeed(effectiveSpeed))
                {
                    hasCompleted = true;
                    return FrameAnimationSessionEvaluation.Failed(
                        FrameAnimationPlaybackErrorCode.InvalidSpeed,
                        "播放期间有效速度变为无效值。");
                }

                if (effectiveSpeed == 0f)
                {
                    return FrameAnimationSessionEvaluation.Running;
                }

                if (IsTerminalLoop(step) && frameIndex == 0 && frameElapsedSeconds <= Epsilon)
                {
                    var cycleRealDuration = GetClipDurationSeconds(step.Clip) / effectiveSpeed;
                    if (cycleRealDuration > Epsilon && remainingRealSeconds >= cycleRealDuration)
                    {
                        remainingRealSeconds %= cycleRealDuration;
                        if (remainingRealSeconds <= Epsilon)
                        {
                            return FrameAnimationSessionEvaluation.Running;
                        }
                    }
                }

                var frame = step.Clip.Frames[frameIndex];
                if (frame == null || frame.DurationMs <= 0)
                {
                    hasCompleted = true;
                    return FrameAnimationSessionEvaluation.Failed(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        "播放期间 Frame 数据失效或 durationMs 不再有效。");
                }

                var frameDurationSeconds = frame.DurationMs / 1000d;
                var remainingAnimationSeconds = Math.Max(0d, frameDurationSeconds - frameElapsedSeconds);
                var realSecondsToBoundary = remainingAnimationSeconds / effectiveSpeed;

                if (remainingRealSeconds + Epsilon < realSecondsToBoundary)
                {
                    frameElapsedSeconds += remainingRealSeconds * effectiveSpeed;
                    return FrameAnimationSessionEvaluation.Running;
                }

                remainingRealSeconds = Math.Max(0d, remainingRealSeconds - realSecondsToBoundary);
                frameElapsedSeconds = 0d;

                var completion = AdvanceFrameOrStep(applySprite);
                if (completion.IsCompleted)
                {
                    return completion;
                }
            }

            return FrameAnimationSessionEvaluation.Running;
        }

        private FrameAnimationSessionEvaluation AdvanceFrameOrStep(Action<Sprite> applySprite)
        {
            var step = CurrentStep;
            frameIndex++;
            if (frameIndex < step.Clip.FrameCount)
            {
                ApplyCurrentFrame(applySprite);
                return FrameAnimationSessionEvaluation.Running;
            }

            var isTerminalStep = stepIndex == plan.Steps.Count - 1;
            if (!isTerminalStep)
            {
                stepIndex++;
                frameIndex = 0;
                ApplyCurrentFrame(applySprite);
                return FrameAnimationSessionEvaluation.Running;
            }

            if (step.TerminalEndBehavior == FrameClipEndBehavior.Loop)
            {
                frameIndex = 0;
                ApplyCurrentFrame(applySprite);
                return FrameAnimationSessionEvaluation.Running;
            }

            frameIndex = step.Clip.FrameCount - 1;
            hasCompleted = true;
            return FrameAnimationSessionEvaluation.Completed(step.TerminalEndBehavior);
        }

        private bool IsTerminalLoop(ResolvedPlaybackStep step)
        {
            return stepIndex == plan.Steps.Count - 1 &&
                   step.TerminalEndBehavior == FrameClipEndBehavior.Loop;
        }

        private static double GetClipDurationSeconds(FrameClip clip)
        {
            return clip.TotalDurationMs / 1000d;
        }

        private void ApplyCurrentFrame(Action<Sprite> applySprite)
        {
            var step = CurrentStep;
            if (step?.Clip == null || frameIndex < 0 || frameIndex >= step.Clip.FrameCount)
            {
                return;
            }

            applySprite?.Invoke(step.Clip.Frames[frameIndex]?.Sprite);
        }
    }
}