using System.Collections.Generic;
using System.Linq;
using UnityEngine;
using BaseGames.Core.Events;

namespace BaseGames.Core
{
    /// <summary>
    /// 状态机核心，持有状态注册表与当前状态。
    /// GameManager 持有一个实例；状态对象在 Awake 注入。
    /// </summary>
    public class GameStateMachine
    {
        private readonly Dictionary<GameStateId, IGameState> _states = new();
        private IGameState _current;

        public GameStateId CurrentStateId => _current?.Id ?? default;

        /// <summary>注册状态实现（同 Id 注册多次以最后一次为准）。</summary>
        public void Register(IGameState state) => _states[state.Id] = state;

        /// <summary>转换到目标状态。失败时返回 false 并填充 error 字符串。</summary>
        public bool TransitionTo(GameStateId nextId, out string error)
        {
            if (!_states.TryGetValue(nextId, out var next))
            {
                error = $"[GameStateMachine] 未知状态 '{nextId}'";
                return false;
            }
            if (_current != null && !_current.ValidNextStates.Contains(nextId))
            {
                error = $"[GameStateMachine] 非法转换 {_current.Id} → {nextId}";
                return false;
            }
            var prev = _current?.Id ?? default;
            _current?.OnExit(nextId);
            _current = next;
            _current.OnEnter(prev);
            error = null;
            return true;
        }

        public void Tick(float deltaTime) => _current?.Tick(deltaTime);
    }
}