using Microsoft.JSInterop;
using System;
using System.Buffers;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Diagnostics;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;

namespace Blazor.Diagrams.Interop
{
    public class BatchJsRuntime : IJSRuntime
    {
        private long _nextId = 1;
        private readonly ConcurrentQueue<JsCall> _calls;
        private readonly ConcurrentDictionary<long, CancellationTokenRegistration> _cancellationRegistrations;
        private readonly IJSRuntime _jsRuntime;
        private Timer _timer;

        public BatchJsRuntime(IJSRuntime jsRuntime)
        {
            _jsRuntime = jsRuntime;
            _calls = new ConcurrentQueue<JsCall>();
            _cancellationRegistrations = new ConcurrentDictionary<long, CancellationTokenRegistration>();
        }

        public JsonSerializerOptions JsonSerializerOptions { get; } = new JsonSerializerOptions
        {
            MaxDepth = 32,
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
            PropertyNameCaseInsensitive = true
        };

        public ValueTask<TValue> InvokeAsync<TValue>(string identifier, object[] args)
        {
            return InvokeAsync<TValue>(identifier, CancellationToken.None, args);
        }

        public ValueTask<TValue> InvokeAsync<TValue>(string identifier, CancellationToken cancellationToken, object[] args)
        {
            var id = Interlocked.Increment(ref _nextId);
            var tcs = new TaskCompletionSource<TValue>();
            var call = new JsCall(id, identifier, args, tcs, typeof(TValue));
            _calls.Enqueue(call);

            // Handle cancellations
            if (cancellationToken.CanBeCanceled)
            {
                _cancellationRegistrations[id] = cancellationToken.Register(() =>
                {
                    tcs.TrySetCanceled(cancellationToken);
                    if (_cancellationRegistrations.TryGetValue(id, out var registration))
                    {
                        registration.Dispose();
                    }
                });
            }

            if (_timer == null)
            {
                _timer = new Timer(OnTimerTick, null, TimeSpan.FromMilliseconds(50), TimeSpan.FromMilliseconds(50));
            }

            return new ValueTask<TValue>(tcs.Task);
        }

        private async void OnTimerTick(object state)
        {
            if (_calls.Count == 0)
                return;

            var currentCalls = new List<JsCall>();
            var callJsObjects = new List<object>();

            while (_calls.TryDequeue(out var call))
            {
                currentCalls.Add(call);
                callJsObjects.Add(new
                {
                    identifier = call.Identifier,
                    args = call.Args != null && call.Args.Length != 0 ? call.Args : null
                });
            }
            
            var results = await _jsRuntime.InvokeAsync<JsResult[]>("batchJsInterop", callJsObjects);

            for (var i = 0; i < results.Length; i++)
            {
                var call = currentCalls[i];
                var result = results[i];

                if (result.Success)
                {
                    object resultObj = result.ReturnValue == null ? null : ToObject((JsonElement)result.ReturnValue, call.Type, JsonSerializerOptions);
                    TcsUtil.SetResult(call.Tcs, call.Type, resultObj);
                }
                else
                {
                    TcsUtil.SetException(call.Tcs, call.Type, new BatchJsException(result.Error));
                }
            }
        }

        private static object ToObject(JsonElement element, Type type, JsonSerializerOptions options = null)
        {
            var bufferWriter = new ArrayBufferWriter<byte>();
            using (var writer = new Utf8JsonWriter(bufferWriter))
            {
                element.WriteTo(writer);
            }

            return JsonSerializer.Deserialize(bufferWriter.WrittenSpan, type, options);
        }
    }
}