using System;
using System.Collections.Generic;
using System.Threading;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Extensions;
using Microsoft.Extensions.Options;
using Umbraco.Cms.Core.Configuration.Models;
using Umbraco.Cms.Core.Events;
using Umbraco.Cms.Core.Notifications;
using Umbraco.Cms.Core.Web;
using Umbraco.Extensions;

namespace Umbraco.Cms.Web.Common.AspNetCore
{
    public class AspNetCoreRequestAccessor : IRequestAccessor, INotificationHandler<UmbracoRequestBeginNotification>
    {
        private readonly IHttpContextAccessor _httpContextAccessor;
        private WebRoutingSettings _webRoutingSettings;
        private readonly ISet<string> _applicationUrls = new HashSet<string>();
        private Uri _currentApplicationUrl;
        private object _initLocker = new object();
        private bool _hasAppUrl = false;
        private bool _isInit = false;

        /// <summary>
        /// Initializes a new instance of the <see cref="AspNetCoreRequestAccessor"/> class.
        /// </summary>
        public AspNetCoreRequestAccessor(
            IHttpContextAccessor httpContextAccessor,
            IOptionsMonitor<WebRoutingSettings> webRoutingSettings)
        {
            _httpContextAccessor = httpContextAccessor;
            _webRoutingSettings = webRoutingSettings.CurrentValue;
            webRoutingSettings.OnChange(x => _webRoutingSettings = x);

        }

        /// <inheritdoc/>
        public string GetRequestValue(string name) => GetFormValue(name) ?? GetQueryStringValue(name);

        private string GetFormValue(string name)
        {
            var request = _httpContextAccessor.GetRequiredHttpContext().Request;
            if (!request.HasFormContentType)
                return null;
            return request.Form[name];
        }

        /// <inheritdoc/>
        public string GetQueryStringValue(string name) => _httpContextAccessor.GetRequiredHttpContext().Request.Query[name];

        /// <inheritdoc/>
        public Uri GetRequestUrl() => _httpContextAccessor.HttpContext != null ? new Uri(_httpContextAccessor.HttpContext.Request.GetEncodedUrl()) : null;

        /// <inheritdoc/>
        public Uri GetApplicationUrl()
        {
            // Fixme: This causes problems with site swap on azure because azure pre-warms a site by calling into `localhost` and when it does that
            // it changes the URL to `localhost:80` which actually doesn't work for pinging itself, it only works internally in Azure. The ironic part
            // about this is that this is here specifically for the slot swap scenario https://issues.umbraco.org/issue/U4-10626

            // see U4-10626 - in some cases we want to reset the application url
            // (this is a simplified version of what was in 7.x)
            // note: should this be optional? is it expensive?

            if (!(_webRoutingSettings.UmbracoApplicationUrl is null))
            {
                return new Uri(_webRoutingSettings.UmbracoApplicationUrl);
            }

            var request = _httpContextAccessor.HttpContext?.Request;

            if (request is null)
            {
                return _currentApplicationUrl;
            }

            var url = UriHelper.BuildAbsolute(request.Scheme, request.Host);
            var change = url != null && !_applicationUrls.Contains(url);
            if (change)
            {
                _applicationUrls.Add(url);

                _currentApplicationUrl ??= new Uri(url);
            }

            return _currentApplicationUrl;
        }

        /// <summary>
        /// This just initializes the application URL on first request attempt
        /// TODO: This doesn't belong here, the GetApplicationUrl doesn't belong to IRequestAccessor
        /// this should be part of middleware not a lazy init based on an INotification
        /// </summary>
        public void Handle(UmbracoRequestBeginNotification notification)
            => LazyInitializer.EnsureInitialized(ref _hasAppUrl, ref _isInit, ref _initLocker, () =>
            {
                GetApplicationUrl();
                return true;
            });
    }
}