using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using Cysharp.Threading.Tasks;
using UnityEngine;

namespace AssetBundleHub
{
    /// <summary>
    /// Fileから非同期でAssetBundleを読むクラス
    /// Readerという名前にすることで「Fileを触るクラス感」を出す。
    /// </summary>
    public interface IAssetBundleReader
    {
        UniTask<AssetBundleRef> LoadFromFileAsync(string path, CancellationToken cancellationToken = default);
    }

    public static class DefaultAssetBundleReader
    {
        // NOTE: 暗号化機能作ったらこの中で分岐する想定
        public static IAssetBundleReader New() => new AssetBundleReader();
    }

    /// <summary>
    /// 暗号化されていないAssetBundleのLoader
    /// </summary>
    public class AssetBundleReader : IAssetBundleReader
    {
        public async UniTask<AssetBundleRef> LoadFromFileAsync(string path, CancellationToken cancellationToken = default)
        {
            var assetBundle = await AssetBundle.LoadFromFileAsync(path, 0).ToUniTask(cancellationToken: cancellationToken);
            return new AssetBundleRef(assetBundle);
        }
    }

    public class XORAssetBundleReader : IAssetBundleReader
    {
        byte[] keyBytes;

        public XORAssetBundleReader(byte[] keyBytes)
        {
            this.keyBytes = keyBytes;
        }

        // NOTE: streamはAssetBundleをUnloadした後にDisposeする必要がある
        // https://docs.unity3d.com/ja/2021.3/ScriptReference/AssetBundle.LoadFromStreamAsync.html
        public async UniTask<AssetBundleRef> LoadFromFileAsync(string path, CancellationToken cancellationToken = default)
        {
            AssetBundle assetBundle = null;
            var fs = new FileStream(path, FileMode.Open);
            var cs = new XORCryptStream(fs, keyBytes);
            assetBundle = await AssetBundle.LoadFromStreamAsync(cs, 0).ToUniTask(cancellationToken: cancellationToken);
            return new AssetBundleRef(assetBundle, new List<IDisposable>() { cs, fs });
        }
    }
}