EmojiStore.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.IO;
using System.Threading.Tasks;
using SimpleJson;
using Json = SimpleJson.SimpleJson;

namespace Emoji
{
	[Export(typeof(IEmojiStore))]
	class EmojiStore : IEmojiStore
	{
		private readonly string _storeDirectory;
		private readonly Downloader _downloader;
		private readonly Dictionary<string, Emoji> _emojis = new Dictionary<string, Emoji>();

		public EmojiStore()
		{
			_storeDirectory = StoreDirectory();
			_downloader = new Downloader();

			if (!Directory.Exists(_storeDirectory))
				Directory.CreateDirectory(_storeDirectory);

			InitializeStore();
		}

		private void InitializeStore()
		{
			Task.Run(async () =>
			{
				try
				{
					var json = await _downloader.DownloadEmojiListAsync();
					InitializeFromJson(json);
					await WriteLocalJsonAsync(json);
				}
				catch
				{
					InitializeFromJson(await ReadLocalJsonAsync());
				}
			});
		}

		private async Task WriteLocalJsonAsync(string json)
		{
			var localJsonFile = Path.Combine(_storeDirectory, "emojis.json");

			using (var file = new FileStream(localJsonFile, File.Exists(localJsonFile) ? FileMode.Truncate : FileMode.OpenOrCreate, FileAccess.Write))
			using (var writer = new StreamWriter(file) { AutoFlush = true })
				await writer.WriteAsync(json);
		}

		private async Task<string> ReadLocalJsonAsync()
		{
			var localJsonFile = Path.Combine(_storeDirectory, "emojis.json");

			using (var file = File.OpenText(localJsonFile))
				return await file.ReadToEndAsync();
		}

		private void InitializeFromJson(string json)
		{
			foreach (var pair in Json.DeserializeObject<JsonObject>(json))
			{
				var name = pair.Key;
				var uri = new Uri((string) pair.Value);

				var emoji = new Emoji(name, uri, EmojiFileName(uri));
				if (!emoji.IsRetrieved)
					DownloadEmoji(emoji);

				_emojis.Add(name, emoji);
			}
		}

		private void DownloadEmoji(Emoji emoji)
		{
			Task.Run(async () => await _downloader.DownloadEmojiAsync(emoji));
		}

		private string EmojiFileName(Uri uri)
		{
			return Path.Combine(_storeDirectory, Path.GetFileName(uri.LocalPath));
		}

		private static string StoreDirectory() => Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "EmojiVS");

		public bool TryGetEmoji(string name, out Emoji emoji)
		{
			return _emojis.TryGetValue(name, out emoji);
		}

		public IEnumerable<Emoji> Emojis()
		{
			return _emojis.Values;
		}
	}
}