using System;
using System.Linq;
using System.Net;
using Microsoft.AspNetCore.Antiforgery;
using Microsoft.Extensions.DependencyInjection;

namespace Microsoft.AspNetCore.Http
{
	/// <summary>
	/// Extensions for the <see cref="HttpContext"/>.
	/// </summary>
	public static class HttpContextExtensions
	{
		// Search these additional headers for a remote client ip address.
		private static readonly string[] _defaultIpHeaderNames = new[]
		{
			"Cf-Connecting-Ip",  // set by Cloudflare
			"X-Real-IP",         // wide-spread alternative to X-Forwarded-For
			"X-Forwarded-For",   // commonly used on all known proxies
		};

		/// <summary>
		/// Retrieves the antiforgery token.
		/// </summary>
		/// <param name="httpContext">The current <see cref="HttpContext"/>.</param>
		/// <returns>FormName, HeaderName and Value of the antiforgery token.</returns>
		public static (string FormName, string HeaderName, string Value) GetAntiforgeryToken(this HttpContext httpContext)
		{
			var antiforgery = httpContext.RequestServices.GetService<IAntiforgery>();
			var tokenSet = antiforgery?.GetAndStoreTokens(httpContext);

			return (tokenSet?.FormFieldName, tokenSet?.HeaderName, tokenSet?.RequestToken);
		}

		/// <summary>
		/// Returns the remote ip address.
		/// </summary>
		/// <remarks>
		/// Searches for additional headers in the following order:
		/// <list type="number">
		/// <item>Cf-Connecting-Ip</item>
		/// <item>X-Real-IP</item>
		/// <item>X-Forwarded-For</item>
		/// </list>
		/// </remarks>
		/// <param name="httpContext">The current <see cref="HttpContext"/>.</param>
		/// <param name="ipHeaderName">The name of the header to resolve the <see cref="IPAddress"/> when behind a proxy.</param>
		/// <returns>The ip address of the client.</returns>
		public static IPAddress GetRemoteIpAddress(this HttpContext httpContext, string ipHeaderName = null)
		{
			string forwardedForAddress = null;

			var headerNames = string.IsNullOrWhiteSpace(ipHeaderName)
				? _defaultIpHeaderNames
				: new[] { ipHeaderName }.Concat(_defaultIpHeaderNames);
			foreach (string headerName in headerNames)
			{
				if (!httpContext.Request.Headers.ContainsKey(headerName))
					continue;

				// X-Forwarded-For can contain multiple comma-separated addresses.
				forwardedForAddress = httpContext.Request.Headers[headerName].ToString()
					.Split(',', StringSplitOptions.TrimEntries)
					.First();

				break;
			}

			if (!string.IsNullOrWhiteSpace(forwardedForAddress) && IPAddress.TryParse(forwardedForAddress, out var remoteAddress))
			{
				return remoteAddress.IsIPv4MappedToIPv6
					? remoteAddress.MapToIPv4()
					: remoteAddress;
			}

			return httpContext.Connection.RemoteIpAddress.IsIPv4MappedToIPv6
				? httpContext.Connection.RemoteIpAddress.MapToIPv4()
				: httpContext.Connection.RemoteIpAddress;
		}

		/// <summary>
		/// Returns whether the request was made locally.
		/// </summary>
		/// <remarks>
		/// Searches for additional headers in the following order:
		/// <list type="number">
		/// <item>Cf-Connecting-Ip</item>
		/// <item>X-Real-IP</item>
		/// <item>X-Forwarded-For</item>
		/// </list>
		/// </remarks>
		/// <param name="httpContext">The current <see cref="HttpContext"/>.</param>
		/// <param name="ipHeaderName">The name of the header to resolve the <see cref="IPAddress"/> when behind a proxy.</param>
		/// <returns></returns>
		public static bool IsLocalRequest(this HttpContext httpContext, string ipHeaderName = null)
		{
			var remoteIpAddress = httpContext.GetRemoteIpAddress(ipHeaderName);
			return httpContext.Connection.LocalIpAddress.Equals(remoteIpAddress);
		}

		/// <summary>
		/// Tries to retrieve the return url.
		/// </summary>
		/// <param name="httpContext">The current <see cref="HttpContext"/>.</param>
		/// <returns></returns>
		public static string GetReturnUrl(this HttpContext httpContext)
		{
			if (httpContext.Items.ContainsKey("OriginalRequest"))
				return httpContext.Items["OriginalRequest"].ToString();

			if (httpContext.Request.Query.ContainsKey("ReturnUrl"))
				return httpContext.Request.Query["ReturnUrl"].ToString();

			return null;
		}

		/// <summary>
		/// Clears a session when available.
		/// </summary>
		/// <param name="httpContext">The current <see cref="HttpContext"/>.</param>
		public static void ClearSession(this HttpContext httpContext)
			=> httpContext.Session?.Clear();
	}
}