using System.Collections.Generic;
using System.Linq;

namespace AibisDream.FrameAnimation
{
    internal sealed class ResolvedPlaybackStep
    {
        public FrameClip Clip { get; }
        public string NodeId { get; }
        public float PlaybackSpeed { get; }
        public FrameClipEndBehavior TerminalEndBehavior { get; }

        public ResolvedPlaybackStep(
            FrameClip clip,
            string nodeId,
            float playbackSpeed,
            FrameClipEndBehavior terminalEndBehavior)
        {
            Clip = clip;
            NodeId = nodeId ?? string.Empty;
            PlaybackSpeed = playbackSpeed;
            TerminalEndBehavior = terminalEndBehavior;
        }
    }

    internal sealed class ResolvedPlaybackPlan
    {
        public string PlayableId { get; }
        public bool IsFlow { get; }
        public IReadOnlyList<ResolvedPlaybackStep> Steps { get; }
        public AnimationFlowAsyncCompletionMode AsyncCompletionMode { get; }

        public ResolvedPlaybackPlan(
            string playableId,
            bool isFlow,
            IReadOnlyList<ResolvedPlaybackStep> steps,
            AnimationFlowAsyncCompletionMode asyncCompletionMode =
                AnimationFlowAsyncCompletionMode.WaitForTerminalLoopFirstCycle)
        {
            PlayableId = playableId;
            IsFlow = isFlow;
            Steps = steps;
            AsyncCompletionMode = asyncCompletionMode;
        }
    }

    internal static class FrameAnimationResolver
    {
        internal static bool TryResolveNode(
            FrameAnimationGraph graph,
            AnimationNode node,
            out ResolvedPlaybackPlan plan,
            out FrameAnimationPlaybackError error)
        {
            plan = null;
            error = FrameAnimationPlaybackError.None;
            if (graph == null)
            {
                error = Error(FrameAnimationPlaybackErrorCode.GraphMissing, "FrameAnimationGraph 为空。");
                return false;
            }
            if (node == null || !graph.Nodes.Contains(node) || node.Type != AnimationNodeType.Clip)
            {
                error = Error(FrameAnimationPlaybackErrorCode.InvalidPlayableData, "AnimationNode 不属于当前 Graph 或类型无效。");
                return false;
            }

            var clips = graph.Clips.Where(clip => clip != null && clip.Id == node.ClipId).ToArray();
            if (clips.Length != 1)
            {
                error = Error(
                    FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                    $"Node '{node.InternalId}' 的 clipId '{node.ClipId}' 不存在或不唯一。");
                return false;
            }
            var clip = clips[0];
            if (!TryValidateClip(clip, out error))
            {
                return false;
            }
            var speed = node.SpeedOverride ?? clip.Speed;
            if (!FrameAnimationValueUtility.IsValidSpeed(speed))
            {
                error = Error(FrameAnimationPlaybackErrorCode.InvalidSpeed, $"Node '{node.InternalId}' 的有效速度无效。");
                return false;
            }

            plan = new ResolvedPlaybackPlan(
                node.InternalId,
                false,
                new[]
                {
                    new ResolvedPlaybackStep(
                        clip,
                        node.InternalId,
                        speed,
                        node.EndBehaviorOverride ?? clip.DefaultEndBehavior)
                });
            return true;
        }

        public static bool TryResolve(
            FrameAnimationGraph graph,
            string playableId,
            FrameAnimationPlayOptions options,
            out ResolvedPlaybackPlan plan,
            out FrameAnimationPlaybackError error)
        {
            plan = null;
            error = FrameAnimationPlaybackError.None;

            if (graph == null)
            {
                error = Error(FrameAnimationPlaybackErrorCode.GraphMissing, "FrameAnimationGraph 为空。");
                return false;
            }

            if (string.IsNullOrWhiteSpace(playableId))
            {
                error = Error(FrameAnimationPlaybackErrorCode.PlayableIdEmpty, "playableId 不能为空。");
                return false;
            }

            var clipMatches = graph.Clips.Where(clip => clip != null && clip.Id == playableId).ToList();
            var flowMatches = graph.Flows.Where(flow => flow != null && flow.Id == playableId).ToList();
            var matchCount = clipMatches.Count + flowMatches.Count;
            if (matchCount == 0)
            {
                error = Error(
                    FrameAnimationPlaybackErrorCode.PlayableNotFound,
                    $"Graph '{graph.Id}' 中不存在 playable '{playableId}'。");
                return false;
            }

            if (matchCount > 1)
            {
                error = Error(
                    FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                    $"playableId '{playableId}' 在 Clip / Flow 统一命名空间中不唯一。");
                return false;
            }

            if (clipMatches.Count == 1)
            {
                return TryResolveClip(clipMatches[0], options, out plan, out error);
            }

            return TryResolveFlow(graph, flowMatches[0], options, out plan, out error);
        }

        internal static bool TryResolveClip(
            FrameClip clip,
            FrameAnimationPlayOptions options,
            out ResolvedPlaybackPlan plan,
            out FrameAnimationPlaybackError error)
        {
            plan = null;
            if (!TryValidateClip(clip, out error))
            {
                return false;
            }

            var endBehavior = options.EndBehaviorOverride ?? clip.DefaultEndBehavior;
            plan = new ResolvedPlaybackPlan(
                clip != null ? clip.Id : string.Empty,
                false,
                new[] { new ResolvedPlaybackStep(clip, string.Empty, clip.Speed, endBehavior) });
            return true;
        }

        private static bool TryResolveFlow(
            FrameAnimationGraph graph,
            AnimationFlow flow,
            FrameAnimationPlayOptions options,
            out ResolvedPlaybackPlan plan,
            out FrameAnimationPlaybackError error)
        {
            plan = null;
            error = FrameAnimationPlaybackError.None;
            var steps = new List<ResolvedPlaybackStep>();
            var visited = new HashSet<string>();
            var currentNodeId = flow.EntryNodeId;
            var topology = new FrameAnimationGraphTopology(graph);

            while (true)
            {
                if (!FrameAnimationValueUtility.IsValidInternalId(currentNodeId))
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Flow '{flow.Id}' 的入口或后继 Node internalId 无效。");
                    return false;
                }

                if (!visited.Add(currentNodeId))
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Flow '{flow.Id}' 的可达路径形成了环路。");
                    return false;
                }

                var nodeMatches = topology.FindNodes(currentNodeId);
                if (nodeMatches.Count != 1)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Flow '{flow.Id}' 的 Node '{currentNodeId}' 不存在或不唯一。");
                    return false;
                }

                var node = nodeMatches[0];
                if (node.Type != AnimationNodeType.Clip)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Node '{node.InternalId}' 使用了第一版不支持的节点类型。");
                    return false;
                }

                var clipMatches = graph.Clips.Where(clip => clip != null && clip.Id == node.ClipId).ToList();
                if (clipMatches.Count != 1)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Node '{node.InternalId}' 的 clipId '{node.ClipId}' 不存在或不唯一。");
                    return false;
                }

                var clip = clipMatches[0];
                if (!TryValidateClip(clip, out error))
                {
                    return false;
                }

                var nodeSpeed = node.SpeedOverride ?? clip.Speed;
                if (!FrameAnimationValueUtility.IsValidSpeed(nodeSpeed))
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidSpeed,
                        $"Node '{node.InternalId}' 的有效播放速度无效。");
                    return false;
                }

                var outgoing = topology.GetOutgoing(currentNodeId);
                if (outgoing.Count > 1)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Node '{node.InternalId}' 第一版最多只能有一个后继 Edge。");
                    return false;
                }

                if (node.EndBehaviorOverride.HasValue && outgoing.Count > 0)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Node '{node.InternalId}' 已设置结束行为，不能同时拥有后继 Edge。");
                    return false;
                }

                var isTerminal = outgoing.Count == 0;
                var terminalBehavior = node.EndBehaviorOverride ??
                                       options.EndBehaviorOverride ??
                                       flow.EndBehaviorOverride ??
                                       clip.DefaultEndBehavior;
                steps.Add(new ResolvedPlaybackStep(clip, node.InternalId, nodeSpeed, terminalBehavior));

                if (isTerminal)
                {
                    break;
                }

                var edge = outgoing[0];
                if (!FrameAnimationValueUtility.IsValidInternalId(edge.InternalId) ||
                    edge.Condition != AnimationEdgeCondition.Always ||
                    edge.FromNodeId == edge.ToNodeId)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Node '{node.InternalId}' 的后继 Edge 无效。");
                    return false;
                }

                currentNodeId = edge.ToNodeId;
            }

            plan = new ResolvedPlaybackPlan(
                flow.Id,
                true,
                steps,
                flow.AsyncCompletionMode);
            return true;
        }

        private static bool TryValidateClip(FrameClip clip, out FrameAnimationPlaybackError error)
        {
            if (clip == null || string.IsNullOrWhiteSpace(clip.Id) || clip.FrameCount == 0)
            {
                error = Error(
                    FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                    "FrameClip 为空、id 为空或没有 Frame。");
                return false;
            }

            if (!FrameAnimationValueUtility.IsValidSpeed(clip.Speed))
            {
                error = Error(
                    FrameAnimationPlaybackErrorCode.InvalidSpeed,
                    $"Clip '{clip.Id}' 的 speed 无效。");
                return false;
            }

            for (var index = 0; index < clip.Frames.Count; index++)
            {
                var frame = clip.Frames[index];
                if (frame == null || frame.DurationMs <= 0)
                {
                    error = Error(
                        FrameAnimationPlaybackErrorCode.InvalidPlayableData,
                        $"Clip '{clip.Id}' 的第 {index} 帧为空或 durationMs 无效。");
                    return false;
                }
            }

            error = FrameAnimationPlaybackError.None;
            return true;
        }

        private static FrameAnimationPlaybackError Error(
            FrameAnimationPlaybackErrorCode code,
            string message)
        {
            return new FrameAnimationPlaybackError(code, message);
        }
    }
}