// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Collections.Generic;
using System.Diagnostics;
using System.Diagnostics.Metrics;
using System.Threading;
 
namespace System.Net.Http
{
    internal static class DiagnosticsHelper
    {
        // OTel bucket boundary recommendation for 'http.request.duration':
        // https://github.com/open-telemetry/semantic-conventions/blob/release/v1.23.x/docs/http/http-metrics.md#metric-httpclientrequestduration
        // We are using the same boundaries for durations which are not expected to be longer than an HTTP request.
        public static InstrumentAdvice<double> ShortHistogramAdvice { get; } = new()
        {
            HistogramBucketBoundaries = [0.005, 0.01, 0.025, 0.05, 0.075, 0.1, 0.25, 0.5, 0.75, 1, 2.5, 5, 7.5, 10]
        };
 
        internal static string GetRedactedUriString(Uri uri)
        {
            Debug.Assert(uri.IsAbsoluteUri);
 
            if (GlobalHttpSettings.DiagnosticsHandler.DisableUriRedaction)
            {
                return uri.AbsoluteUri;
            }
 
            string pathAndQuery = uri.PathAndQuery;
            int queryIndex = pathAndQuery.IndexOf('?');
 
            bool redactQuery = queryIndex >= 0 && // Query is present.
                queryIndex < pathAndQuery.Length - 1; // Query is not empty.
 
            return (redactQuery, uri.IsDefaultPort) switch
            {
                (true, true) => $"{uri.Scheme}://{uri.Host}{pathAndQuery.AsSpan(0, queryIndex + 1)}*",
                (true, false) => $"{uri.Scheme}://{uri.Host}:{uri.Port}{pathAndQuery.AsSpan(0, queryIndex + 1)}*",
                (false, true) => $"{uri.Scheme}://{uri.Host}{pathAndQuery}",
                (false, false) => $"{uri.Scheme}://{uri.Host}:{uri.Port}{pathAndQuery}"
            };
        }
 
        internal static KeyValuePair<string, object?> GetMethodTag(HttpMethod method, out bool isUnknownMethod)
        {
            // Return canonical names for known methods and "_OTHER" for unknown ones.
            HttpMethod? known = HttpMethod.GetKnownMethod(method.Method);
            isUnknownMethod = known is null;
            return new KeyValuePair<string, object?>("http.request.method", isUnknownMethod ? "_OTHER" : known!.Method);
        }
 
        internal static string GetProtocolVersionString(Version httpVersion) => (httpVersion.Major, httpVersion.Minor) switch
        {
            (1, 0) => "1.0",
            (1, 1) => "1.1",
            (2, 0) => "2",
            (3, 0) => "3",
            _ => httpVersion.ToString()
        };
 
        public static bool TryGetErrorType(HttpResponseMessage? response, Exception? exception, out string? errorType)
        {
            if (response is not null)
            {
                int statusCode = (int)response.StatusCode;
 
                // In case the status code indicates a client or a server error, return the string representation of the status code.
                // See the paragraph Status and the definition of 'error.type' in
                // https://github.com/open-telemetry/semantic-conventions/blob/release/v1.23.x/docs/http/http-spans.md#Status
                if (statusCode >= 400 && statusCode <= 599)
                {
                    errorType = GetErrorStatusCodeString(statusCode);
                    return true;
                }
            }
 
            if (exception is null)
            {
                errorType = null;
                return false;
            }
 
            Debug.Assert(Enum.GetValues<HttpRequestError>().Length == 12, "We need to extend the mapping in case new values are added to HttpRequestError.");
            errorType = (exception as HttpRequestException)?.HttpRequestError switch
            {
                HttpRequestError.NameResolutionError => "name_resolution_error",
                HttpRequestError.ConnectionError => "connection_error",
                HttpRequestError.SecureConnectionError => "secure_connection_error",
                HttpRequestError.HttpProtocolError => "http_protocol_error",
                HttpRequestError.ExtendedConnectNotSupported => "extended_connect_not_supported",
                HttpRequestError.VersionNegotiationError => "version_negotiation_error",
                HttpRequestError.UserAuthenticationError => "user_authentication_error",
                HttpRequestError.ProxyTunnelError => "proxy_tunnel_error",
                HttpRequestError.InvalidResponse => "invalid_response",
                HttpRequestError.ResponseEnded => "response_ended",
                HttpRequestError.ConfigurationLimitExceeded => "configuration_limit_exceeded",
 
                // Fall back to the exception type name in case of HttpRequestError.Unknown or when exception is not an HttpRequestException.
                _ => exception.GetType().FullName!
            };
            return true;
        }
 
        private static object[]? s_boxedStatusCodes;
        private static string[]? s_statusCodeStrings;
 
#pragma warning disable CA1859 // we explictly box here
        // Returns a pooled object if 'value' is between 0-512,
        // saving allocations for standard HTTP status codes and small port tag values.
        public static object GetBoxedInt32(int value)
        {
            object[] boxes = LazyInitializer.EnsureInitialized(ref s_boxedStatusCodes, static () => new object[512]);
 
            return (uint)value < (uint)boxes.Length
                ? boxes[value] ??= value
                : value;
        }
#pragma warning restore
 
        private static string GetErrorStatusCodeString(int statusCode)
        {
            Debug.Assert(statusCode >= 400 && statusCode <= 599);
 
            string[] strings = LazyInitializer.EnsureInitialized(ref s_statusCodeStrings, static () => new string[200]);
            int index = statusCode - 400;
            return (uint)index < (uint)strings.Length
                ? strings[index] ??= statusCode.ToString()
                : statusCode.ToString();
        }
    }
}