using System;
using System.IO;
using System.Runtime.Serialization.Json;
using System.Text;

namespace Prophet.CoopWithDsh
{
    internal sealed class SnapshotPublisher : IDisposable
    {
        private static readonly DataContractJsonSerializer Serializer = new DataContractJsonSerializer(typeof(OpenFileSnapshot));
        private readonly object gate = new object();
        internal string InstanceId { get; } = Guid.NewGuid().ToString("N");
        internal string FilePath { get; }

        internal SnapshotPublisher(string? localAppData = null)
        {
            var root = localAppData ?? Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData);
            if (string.IsNullOrWhiteSpace(root)) throw new InvalidOperationException("LOCALAPPDATA is unavailable.");
            var directory = Path.Combine(root, "Prophet", "dsh-plugin-coop-with-vs", "v1", "instances");
            FilePath = Path.Combine(directory, $"visualstudio-{InstanceId}.json");
        }

        internal void Publish(OpenFileSnapshot snapshot)
        {
            lock (gate)
            {
                var directory = Path.GetDirectoryName(FilePath)!;
                Directory.CreateDirectory(directory);
                var temporary = FilePath + "." + Guid.NewGuid().ToString("N") + ".tmp";
                using (var stream = new MemoryStream())
                {
                    Serializer.WriteObject(stream, snapshot);
                    File.WriteAllText(temporary, Encoding.UTF8.GetString(stream.ToArray()) + Environment.NewLine, new UTF8Encoding(false));
                }
                try
                {
                    if (File.Exists(FilePath)) File.Replace(temporary, FilePath, null);
                    else File.Move(temporary, FilePath);
                }
                catch
                {
                    TryDelete(temporary);
                    throw;
                }
            }
        }

        public void Dispose() => TryDelete(FilePath);

        private static void TryDelete(string path)
        {
            try { if (File.Exists(path)) File.Delete(path); } catch { }
        }
    }
}