using System;
using System.Globalization;
using System.Net;
using Cysharp.Threading.Tasks;
using UniRx;

public class NetTime : LazySingleton<NetTime>
{
    public readonly ReactiveProperty<bool> IsAvailable = new ReactiveProperty<bool>();
    public IObservable<bool> IsAvailableAsObservable() => IsAvailable;
    public DateTime Time => DateTime.Now + _timeDelta;

    private TimeSpan _timeDelta = TimeSpan.Zero;

    private static async UniTask<DateTime> GetTimeAsync()
    {
        using (var response =
            await WebRequest.Create("https://www.google.com").GetResponseAsync())
            return DateTime.ParseExact(response.Headers["date"],
                "ddd, dd MMM yyyy HH:mm:ss 'GMT'",
                CultureInfo.InvariantCulture.DateTimeFormat,
                DateTimeStyles.AssumeUniversal);
    }


    private void Awake()
    {
        UniTask.Run(CacheTimeAsync);
    }

    private void OnApplicationFocus(bool hasFocus)
    {
        if (hasFocus == false)
        {
            IsAvailable.Value = false;
            return;
        }

        UniTask.Run(CacheTimeAsync);
    }

    private async void CacheTimeAsync()
    {
        try
        {
            var googleTime = await GetTimeAsync();
            var deviceTime = DateTime.Now;
            _timeDelta = googleTime - deviceTime;
            IsAvailable.Value = true;
        }
        catch (Exception)
        {
            Log.Error("Can't connect with google.");
        }
    }
}