using System;
using System.Collections.Generic;

namespace AibisDream
{
    /// <summary>
    /// 从现有 TalkSceneSO 图派生的运行时索引，不引入第二份章节创作数据。
    /// </summary>
    public sealed class TalkSceneGraphIndex
    {
        private readonly List<TalkSceneSO> _runtimeChapters = new();
        private readonly Dictionary<string, TalkSceneSO> _byName = new(StringComparer.Ordinal);
        private readonly HashSet<string> _ambiguousNames = new(StringComparer.Ordinal);
        private readonly List<string> _validationErrors = new();

        public IReadOnlyList<TalkSceneSO> RuntimeChapters => _runtimeChapters;
        public IReadOnlyList<string> ValidationErrors => _validationErrors;

        public TalkSceneGraphIndex(TalkSceneSO firstTalkScene)
        {
            var visited = new HashSet<TalkSceneSO>();
            VisitRuntime(firstTalkScene, visited);
        }

        public bool TryFindByName(string sceneName, out TalkSceneSO scene, out string error)
        {
            scene = null;
            if (string.IsNullOrWhiteSpace(sceneName))
            {
                error = "TalkSceneSO name is empty.";
                return false;
            }

            if (_ambiguousNames.Contains(sceneName))
            {
                error = $"TalkSceneSO name is ambiguous: {sceneName}.";
                return false;
            }

            if (!_byName.TryGetValue(sceneName, out scene) || scene == null)
            {
                error = $"TalkSceneSO does not exist: {sceneName}.";
                return false;
            }

            error = null;
            return true;
        }

        private void VisitRuntime(TalkSceneSO scene, ISet<TalkSceneSO> visited)
        {
            if (scene == null || !visited.Add(scene))
            {
                return;
            }

            _runtimeChapters.Add(scene);
            IndexByName(scene);

            if (scene.exits == null)
            {
                return;
            }

            foreach (var exit in scene.exits)
            {
                VisitRuntime(exit?.targetScene, visited);
            }
        }

        private void IndexByName(TalkSceneSO scene)
        {
            if (scene == null)
            {
                return;
            }

            var sceneName = scene.name;
            if (string.IsNullOrWhiteSpace(sceneName))
            {
                _validationErrors.Add("TalkSceneSO has an empty asset name.");
                return;
            }

            if (_byName.TryGetValue(sceneName, out var existing))
            {
                if (existing != scene && _ambiguousNames.Add(sceneName))
                {
                    _validationErrors.Add($"Duplicate TalkSceneSO name: {sceneName}.");
                }

                return;
            }

            _byName.Add(sceneName, scene);
        }
    }
}