using System.Diagnostics;

namespace PrivaPub.Infrastructure.Statistics
{
	public static class TrafficMeter
	{
		public static IApplicationBuilder UseTrafficMeter(this IApplicationBuilder app) =>
			app.Use(async (context, next) =>
			{
				var started = Stopwatch.GetTimestamp();
				try
				{
					await next(context);
				}
				finally
				{
					Count(context, (int)Stopwatch.GetElapsedTime(started).TotalMilliseconds);
				}
			});

		static void Count(HttpContext context, int latencyMs)
		{
			var ledger = context.RequestServices?.GetService<IInteractionLedger>();
			if (ledger == default)
				return;
			var path = context.Request.Path;
			var template = (context.GetEndpoint() as RouteEndpoint)?.RoutePattern.RawText;
			var method = context.Request.Method;
			var status = context.Response.StatusCode;
			if (path.StartsWithSegments("/api") || path.StartsWithSegments("/oauth") || path.StartsWithSegments("/clientapi"))
			{
				ledger.CountServer(ServerSections.Client, $"{Group(template)}:{method}:{status / 100}xx", latencyMs);
				return;
			}
			if (method != HttpMethods.Get && method != HttpMethods.Head)
				return;
			var served = Served(template, path);
			if (served != default)
				ledger.CountServer(ServerSections.Served,
					$"{served}:{status}:{(context.Request.Headers.ContainsKey("Signature") || context.Request.Headers.ContainsKey("Signature-Input") ? "signed" : "unsigned")}");
		}

		public static string Group(string template)
		{
			if (template == default)
				return "unmatched";
			var literals = template.Trim('/').Split('/', StringSplitOptions.RemoveEmptyEntries)
				.TakeWhile(segment => !segment.Contains('{'))
				.Take(3);
			var group = string.Join('/', literals);
			return group.Length == 0 ? "unmatched" : group;
		}

		public static string Served(string template, PathString path)
		{
			if (path.StartsWithSegments("/.well-known/webfinger"))
				return "webfinger";
			if (path.StartsWithSegments("/.well-known/nodeinfo") || path.StartsWithSegments("/nodeinfo"))
				return "nodeinfo";
			if (!path.StartsWithSegments("/peasants") && !path.StartsWithSegments("/users"))
				return default;
			var segments = (template ?? path.Value ?? string.Empty).Trim('/').Split('/');
			return segments.Length switch
			{
				<= 2 => "actor",
				_ => segments[2] switch
				{
					"anus" => "outbox",
					"scribbles" or "whispers" => "object",
					"grunts" => "activity",
					"parrot-licences" => "licence",
					"mouth" or "human-centipede" => default,
					_ => "collection"
				}
			};
		}
	}
}