using System;
using System.Collections.Generic;
using UnityEngine.Networking;
using UnityEngine.ResourceManagement.Util;

namespace UnityEngine.ResourceManagement
{
    internal class WebRequestQueueOperation
    {
        private bool m_Completed = false;
        public UnityWebRequestAsyncOperation Result;
        public Action<UnityWebRequestAsyncOperation> OnComplete;

        public bool IsDone
        {
            get { return m_Completed || Result != null; }
        }

        internal UnityWebRequest m_WebRequest;

        public WebRequestQueueOperation(UnityWebRequest request)
        {
            m_WebRequest = request;
        }

        internal void Complete(UnityWebRequestAsyncOperation asyncOp)
        {
            m_Completed = true;
            Result = asyncOp;
            OnComplete?.Invoke(Result);
        }
    }


    internal static class WebRequestQueue
    {
        internal static int s_MaxRequest = 500;
        internal static Queue<WebRequestQueueOperation> s_QueuedOperations = new Queue<WebRequestQueueOperation>();
        internal static List<UnityWebRequestAsyncOperation> s_ActiveRequests = new List<UnityWebRequestAsyncOperation>();
        public static void SetMaxConcurrentRequests(int maxRequests)
        {
            if (maxRequests < 1)
                throw new ArgumentException("MaxRequests must be 1 or greater.", "maxRequests");
            s_MaxRequest = maxRequests;
        }

        public static WebRequestQueueOperation QueueRequest(UnityWebRequest request)
        {
            WebRequestQueueOperation queueOperation = new WebRequestQueueOperation(request);
            if (s_ActiveRequests.Count < s_MaxRequest)
            {
                UnityWebRequestAsyncOperation webRequestAsyncOp = null;
                try
                {
                    webRequestAsyncOp = request.SendWebRequest();
                    s_ActiveRequests.Add(webRequestAsyncOp);

                    if (webRequestAsyncOp.isDone)
                        OnWebAsyncOpComplete(webRequestAsyncOp);
                    else
                        webRequestAsyncOp.completed += OnWebAsyncOpComplete;
                }
                catch (Exception e)
                {
                    Debug.LogError(e.Message);
                }

                queueOperation.Complete(webRequestAsyncOp);
            }
            else
                s_QueuedOperations.Enqueue(queueOperation);

            return queueOperation;
        }

        internal static void WaitForRequestToBeActive(WebRequestQueueOperation request, int millisecondsTimeout)
        {
            var completedRequests = new List<UnityWebRequestAsyncOperation>();
            while (s_QueuedOperations.Contains(request))
            {
                completedRequests.Clear();
                foreach (UnityWebRequestAsyncOperation webRequestAsyncOp in s_ActiveRequests)
                {
                    if (UnityWebRequestUtilities.IsAssetBundleDownloaded(webRequestAsyncOp))
                        completedRequests.Add(webRequestAsyncOp);
                }
                foreach (UnityWebRequestAsyncOperation webRequestAsyncOp in completedRequests)
                {
                    bool requestIsActive = s_QueuedOperations.Peek() == request;
                    webRequestAsyncOp.completed -= OnWebAsyncOpComplete;
                    OnWebAsyncOpComplete(webRequestAsyncOp);
                    if (requestIsActive)
                        return;
                }
                System.Threading.Thread.Sleep(millisecondsTimeout);
            }
        }

        private static void OnWebAsyncOpComplete(AsyncOperation operation)
        {
            s_ActiveRequests.Remove((operation as UnityWebRequestAsyncOperation));

            if (s_QueuedOperations.Count > 0)
            {
                var nextQueuedOperation = s_QueuedOperations.Dequeue();
                var webRequestAsyncOp = nextQueuedOperation.m_WebRequest.SendWebRequest();
                webRequestAsyncOp.completed += OnWebAsyncOpComplete;
                s_ActiveRequests.Add(webRequestAsyncOp);
                nextQueuedOperation.Complete(webRequestAsyncOp);
            }
        }
    }
}