using UnityEngine;
using UnityEngine.Events;

namespace AssetManagement
{
    public abstract class AsyncLoadUnit
    {
        protected AssetPathHub pathHub;
        public string name { get; private set; }
        public int priority { get; set; }
        public string error { get; private set; }
        public AsyncLoadUnitState state { get; private set; }
        public event UnityAction<AsyncLoadUnit> onComplete;

        public void Init(AssetPathHub pathHub, string assetName, int priority)
        {
            name = assetName;
            this.priority = priority;
            this.pathHub = pathHub;
        }

        public void Load()
        {
            if (state != AsyncLoadUnitState.Loading)
            {
                string startError;
                var operation = StartOperation(out startError);
                error = startError;
                if (string.IsNullOrEmpty(error))
                    operation.completed += OnOperationComplete;
                state = string.IsNullOrEmpty(error) ? AsyncLoadUnitState.Loading : AsyncLoadUnitState.Done;
            }
        }
        
        public abstract float GetProgress();

        /// <summary>
        ///     开始当前配置的任务
        /// </summary>
        protected abstract AsyncOperation StartOperation(out string startError);

        /// <summary>
        ///     处理完成的任务，并返回错误
        /// </summary>
        protected abstract string HandleOperation(AsyncOperation operation);

        private void OnOperationComplete(AsyncOperation operation)
        {
            error = HandleOperation(operation);
            state = AsyncLoadUnitState.Done;
            if (onComplete != null)
                onComplete(this);
        }
    }

    public enum AsyncLoadUnitState
    {
        Idle,
        Loading,
        Done,
    }
}