Google API's AppDataFileStore

AppDataFileStore.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

using System.IO;
using System.Threading;
using System.Threading.Tasks;

using Google.Apis.Util.Store;
using Google.Apis.Json;

namespace Google.Apis.Util.Store {
    public class AppDataFileStore : IDataStore {
        readonly string folderPath;
        /// <summary>Gets the full folder path.</summary>
        public string FolderPath { get { return folderPath; } }

        /// <summary>
        /// Constructs a new file data store with the specified folder. This folder is created (if it doesn't exist
        /// yet) under <see cref="Environment.SpecialFolder.ApplicationData"/>.
        /// </summary>
        /// <param name="folder">Folder name.</param>
        public AppDataFileStore(string folder) {
            folderPath = Path.Combine(HttpContext.Current.Server.MapPath("~/App_Data/"), folder);
            if (!Directory.Exists(folderPath)) {
                Directory.CreateDirectory(folderPath);
            }
        }

        /// <summary>
        /// Stores the given value for the given key. It creates a new file (named <see cref="GenerateStoredKey"/>) in
        /// <see cref="FolderPath"/>.
        /// </summary>
        /// <typeparam name="T">The type to store in the data store.</typeparam>
        /// <param name="key">The key.</param>
        /// <param name="value">The value to store in the data store.</param>
        public Task StoreAsync<T>(string key, T value) {
            if (string.IsNullOrEmpty(key)) {
                throw new ArgumentException("Key MUST have a value");
            }

            var serialized = NewtonsoftJsonSerializer.Instance.Serialize(value);
            var filePath = Path.Combine(folderPath, GenerateStoredKey(key, typeof(T)));
            File.WriteAllText(filePath, serialized);
            return TaskEx.Delay(0);
        }

        /// <summary>
        /// Deletes the given key. It deletes the <see cref="GenerateStoredKey"/> named file in
        /// <see cref="FolderPath"/>.
        /// </summary>
        /// <param name="key">The key to delete from the data store.</param>
        public Task DeleteAsync<T>(string key) {
            if (string.IsNullOrEmpty(key)) {
                throw new ArgumentException("Key MUST have a value");
            }

            var filePath = Path.Combine(folderPath, GenerateStoredKey(key, typeof(T)));
            if (File.Exists(filePath)) {
                File.Delete(filePath);
            }
            return TaskEx.Delay(0);
        }

        /// <summary>
        /// Returns the stored value for the given key or <c>null</c> if the matching file (<see cref="GenerateStoredKey"/>
        /// in <see cref="FolderPath"/> doesn't exist.
        /// </summary>
        /// <typeparam name="T">The type to retrieve.</typeparam>
        /// <param name="key">The key to retrieve from the data store.</param>
        /// <returns>The stored object.</returns>
        public Task<T> GetAsync<T>(string key) {
            if (string.IsNullOrEmpty(key)) {
                throw new ArgumentException("Key MUST have a value");
            }

            TaskCompletionSource<T> tcs = new TaskCompletionSource<T>();
            var filePath = Path.Combine(folderPath, GenerateStoredKey(key, typeof(T)));
            if (File.Exists(filePath)) {
                try {
                    var obj = File.ReadAllText(filePath);
                    tcs.SetResult(NewtonsoftJsonSerializer.Instance.Deserialize<T>(obj));
                }
                catch (Exception ex) {
                    tcs.SetException(ex);
                }
            }
            else {
                tcs.SetResult(default(T));
            }
            return tcs.Task;
        }

        /// <summary>
        /// Clears all values in the data store. This method deletes all files in <see cref="FolderPath"/>.
        /// </summary>
        public Task ClearAsync() {
            if (Directory.Exists(folderPath)) {
                Directory.Delete(folderPath, true);
                Directory.CreateDirectory(folderPath);
            }

            return TaskEx.Delay(0);
        }

        /// <summary>Creates a unique stored key based on the key and the class type.</summary>
        /// <param name="key">The object key.</param>
        /// <param name="t">The type to store or retrieve.</param>
        public static string GenerateStoredKey(string key, Type t) {
            return string.Format("{0}-{1}", t.FullName, key);
        }
    }
}