using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.SceneManagement;

namespace AibisDream
{
    public sealed class SceneReadinessResult
    {
        public bool Success { get; internal set; }
        public bool Cancelled { get; internal set; }
        public string Error { get; internal set; }
    }

    public static class SceneReadiness
    {
        public const float DefaultTimeoutSeconds = 15f;

        public static IEnumerator WaitUntilReady(
            Scene scene,
            Func<bool> isCancellationRequested,
            Action<SceneReadinessResult> completed,
            float timeoutSeconds = DefaultTimeoutSeconds)
        {
            var result = new SceneReadinessResult();

            // 等待场景内 Awake/Start 完成，再收集当前场景自己的 Gate。
            yield return null;

            if (isCancellationRequested?.Invoke() == true)
            {
                result.Cancelled = true;
                result.Error = "Scene readiness was cancelled.";
                completed?.Invoke(result);
                yield break;
            }

            if (!scene.IsValid() || !scene.isLoaded)
            {
                result.Error = "Loaded scene is invalid or not loaded.";
                completed?.Invoke(result);
                yield break;
            }

            var gates = CollectGates(scene);
            if (gates.Count == 0)
            {
                result.Success = true;
                completed?.Invoke(result);
                yield break;
            }

            var deadline = Time.unscaledTime + Mathf.Max(0f, timeoutSeconds);
            while (true)
            {
                if (isCancellationRequested?.Invoke() == true)
                {
                    result.Cancelled = true;
                    result.Error = "Scene readiness was cancelled.";
                    break;
                }

                var allReady = true;
                foreach (var gate in gates)
                {
                    if (gate is UnityEngine.Object unityObject && unityObject == null)
                    {
                        result.Error = "A scene dialogue gate was destroyed while waiting.";
                        completed?.Invoke(result);
                        yield break;
                    }

                    if (!gate.IsDialogueReady)
                    {
                        allReady = false;
                    }
                }

                if (allReady)
                {
                    result.Success = true;
                    break;
                }

                if (Time.unscaledTime >= deadline)
                {
                    result.Error = $"Scene readiness timed out after {timeoutSeconds:0.#} seconds.";
                    break;
                }

                yield return null;
            }

            completed?.Invoke(result);
        }

        private static List<ISceneDialogueGate> CollectGates(Scene scene)
        {
            var gates = new List<ISceneDialogueGate>();
            foreach (var root in scene.GetRootGameObjects())
            {
                foreach (var behaviour in root.GetComponentsInChildren<MonoBehaviour>(true))
                {
                    if (behaviour is ISceneDialogueGate gate)
                    {
                        gates.Add(gate);
                    }
                }
            }

            return gates;
        }
    }
}