using System;
using System.IO;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using UnityEngine;

namespace FlowScope.Save
{
    public interface ISaveStorage
    {
        Task WriteAsync(string key, byte[] data, CancellationToken cancellationToken);
        Task<byte[]> ReadAsync(string key, CancellationToken cancellationToken);
        void Delete(string key);
        bool Exists(string key);
    }

    public sealed class FileSaveStorage : ISaveStorage
    {
        private readonly string _rootDirectory;

        public FileSaveStorage(string rootDirectory = null)
        {
            _rootDirectory = string.IsNullOrWhiteSpace(rootDirectory)
                ? Path.Combine(Application.persistentDataPath, "FlowScopeSaves")
                : rootDirectory;
        }

        public async Task WriteAsync(string key, byte[] data, CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();
            if (data == null)
            {
                throw new ArgumentNullException(nameof(data));
            }

            Directory.CreateDirectory(_rootDirectory);
            var path = GetPath(key);
            using var stream = new FileStream(path, FileMode.Create, FileAccess.Write, FileShare.None, 4096, true);
            await stream.WriteAsync(data, 0, data.Length, cancellationToken);
        }

        public async Task<byte[]> ReadAsync(string key, CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();
            var path = GetPath(key);
            if (!File.Exists(path))
            {
                return null;
            }

            using var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, 4096, true);
            var data = new byte[stream.Length];
            var read = 0;
            while (read < data.Length)
            {
                var count = await stream.ReadAsync(data, read, data.Length - read, cancellationToken);
                if (count == 0)
                {
                    break;
                }

                read += count;
            }

            return data;
        }

        public void Delete(string key)
        {
            var path = GetPath(key);
            if (File.Exists(path))
            {
                File.Delete(path);
            }
        }

        public bool Exists(string key)
        {
            return File.Exists(GetPath(key));
        }

        private string GetPath(string key)
        {
            if (string.IsNullOrWhiteSpace(key))
            {
                throw new ArgumentException("Save key is required.", nameof(key));
            }

            return Path.Combine(_rootDirectory, Convert.ToBase64String(Encoding.UTF8.GetBytes(key)) + ".json");
        }
    }
}