using System.Diagnostics.Metrics;
using System.Net;
using System.Net.Http.Headers;
using System.Net.Http.Json;
using System.Text.Json;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Testing;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.IdentityModel.JsonWebTokens;
using Microsoft.IdentityModel.Protocols.OpenIdConnect;
using Microsoft.IdentityModel.Tokens;
using Polly.Utilities;
using StellaOps.Auth.Client;
using StellaOps.Auth.Abstractions;
using StellaOps.Policy.Gateway.Clients;
using StellaOps.Policy.Gateway.Contracts;
using StellaOps.Policy.Gateway.Options;
using StellaOps.Policy.Gateway.Services;
using Xunit;
using Xunit.Sdk;

namespace StellaOps.Policy.Gateway.Tests;

public sealed class GatewayActivationTests
{
    [Fact]
    public async Task ActivateRevision_UsesServiceTokenFallback_And_RecordsMetrics()
    {
        await using var factory = new PolicyGatewayWebApplicationFactory();

        var tokenClient = factory.Services.GetRequiredService<StubTokenClient>();
        tokenClient.Reset();

        var recordingHandler = factory.Services.GetRequiredService<RecordingPolicyEngineHandler>();
        recordingHandler.Reset();

        using var listener = new MeterListener();
        var activationMeasurements = new List<(long Value, string Outcome, string Source)>();
        var latencyMeasurements = new List<(double Value, string Outcome, string Source)>();

        listener.InstrumentPublished += (instrument, meterListener) =>
        {
            if (instrument.Meter.Name != "StellaOps.Policy.Gateway")
            {
                return;
            }

            meterListener.EnableMeasurementEvents(instrument);
        };

        listener.SetMeasurementEventCallback<long>((instrument, value, tags, _) =>
        {
            if (instrument.Name != "policy_gateway_activation_requests_total")
            {
                return;
            }

            activationMeasurements.Add((value, GetTag(tags, "outcome"), GetTag(tags, "source")));
        });

        listener.SetMeasurementEventCallback<double>((instrument, value, tags, _) =>
        {
            if (instrument.Name != "policy_gateway_activation_latency_ms")
            {
                return;
            }

            latencyMeasurements.Add((value, GetTag(tags, "outcome"), GetTag(tags, "source")));
        });

        listener.Start();

        using var client = factory.CreateClient();

        var response = await client.PostAsJsonAsync(
            "/api/policy/packs/example/revisions/5:activate",
            new ActivatePolicyRevisionRequest("rollout window start"));

        listener.Dispose();

        var forwardedRequest = recordingHandler.LastRequest;
        var issuedTokens = tokenClient.RequestCount;
        var responseBody = await response.Content.ReadAsStringAsync();
        if (!response.IsSuccessStatusCode)
        {
            throw new Xunit.Sdk.XunitException(
                $"Gateway response was {(int)response.StatusCode} {response.StatusCode}. " +
                $"Body: {responseBody}. IssuedTokens: {issuedTokens}. Forwarded: { (forwardedRequest is null ? "no" : "yes") }.");
        }

        Assert.Equal(1, tokenClient.RequestCount);

        Assert.NotNull(forwardedRequest);
        Assert.Equal(HttpMethod.Post, forwardedRequest!.Method);
        Assert.Equal("https://policy-engine.test/api/policy/packs/example/revisions/5:activate", forwardedRequest.RequestUri!.ToString());
        Assert.Equal("Bearer", forwardedRequest.Headers.Authorization?.Scheme);
        Assert.Equal("service-token", forwardedRequest.Headers.Authorization?.Parameter);
        Assert.False(forwardedRequest.Headers.TryGetValues("DPoP", out _), "Expected no DPoP header when DPoP is disabled.");

        Assert.Contains(activationMeasurements, measurement =>
            measurement.Value == 1 &&
            measurement.Outcome == "activated" &&
            measurement.Source == "service");

        Assert.Contains(latencyMeasurements, measurement =>
            measurement.Outcome == "activated" &&
            measurement.Source == "service");
    }

    [Fact]
    public async Task ActivateRevision_RecordsMetrics_WhenUpstreamReturnsUnauthorized()
    {
        await using var factory = new PolicyGatewayWebApplicationFactory();

        var tokenClient = factory.Services.GetRequiredService<StubTokenClient>();
        tokenClient.Reset();

        var recordingHandler = factory.Services.GetRequiredService<RecordingPolicyEngineHandler>();
        recordingHandler.Reset();
        recordingHandler.SetResponseFactory(_ =>
        {
            var problem = new ProblemDetails
            {
                Title = "Unauthorized",
                Detail = "Caller token rejected.",
                Status = StatusCodes.Status401Unauthorized
            };
            return new HttpResponseMessage(HttpStatusCode.Unauthorized)
            {
                Content = JsonContent.Create(problem)
            };
        });

        using var listener = new MeterListener();
        var activationMeasurements = new List<(long Value, string Outcome, string Source)>();
        var latencyMeasurements = new List<(double Value, string Outcome, string Source)>();

        listener.InstrumentPublished += (instrument, meterListener) =>
        {
            if (instrument.Meter.Name != "StellaOps.Policy.Gateway")
            {
                return;
            }

            meterListener.EnableMeasurementEvents(instrument);
        };

        listener.SetMeasurementEventCallback<long>((instrument, value, tags, _) =>
        {
            if (instrument.Name != "policy_gateway_activation_requests_total")
            {
                return;
            }

            activationMeasurements.Add((value, GetTag(tags, "outcome"), GetTag(tags, "source")));
        });

        listener.SetMeasurementEventCallback<double>((instrument, value, tags, _) =>
        {
            if (instrument.Name != "policy_gateway_activation_latency_ms")
            {
                return;
            }

            latencyMeasurements.Add((value, GetTag(tags, "outcome"), GetTag(tags, "source")));
        });

        listener.Start();

        using var client = factory.CreateClient();

        var response = await client.PostAsJsonAsync(
            "/api/policy/packs/example/revisions/2:activate",
            new ActivatePolicyRevisionRequest("failure path"));

        listener.Dispose();

        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);

        Assert.Equal(1, tokenClient.RequestCount);

        var forwardedRequest = recordingHandler.LastRequest;
        Assert.NotNull(forwardedRequest);
        Assert.Equal("service-token", forwardedRequest!.Headers.Authorization?.Parameter);

        Assert.Contains(activationMeasurements, measurement =>
            measurement.Value == 1 &&
            measurement.Outcome == "unauthorized" &&
            measurement.Source == "service");

        Assert.Contains(latencyMeasurements, measurement =>
            measurement.Outcome == "unauthorized" &&
            measurement.Source == "service");
    }

    [Fact]
    public async Task ActivateRevision_RecordsMetrics_WhenUpstreamReturnsBadGateway()
    {
        await using var factory = new PolicyGatewayWebApplicationFactory();

        var tokenClient = factory.Services.GetRequiredService<StubTokenClient>();
        tokenClient.Reset();

        var recordingHandler = factory.Services.GetRequiredService<RecordingPolicyEngineHandler>();
        recordingHandler.Reset();
        recordingHandler.SetResponseFactory(_ =>
        {
            var problem = new ProblemDetails
            {
                Title = "Upstream error",
                Detail = "Policy Engine returned 502.",
                Status = StatusCodes.Status502BadGateway
            };
            return new HttpResponseMessage(HttpStatusCode.BadGateway)
            {
                Content = JsonContent.Create(problem)
            };
        });

        using var listener = new MeterListener();
        var activationMeasurements = new List<(long Value, string Outcome, string Source)>();
        var latencyMeasurements = new List<(double Value, string Outcome, string Source)>();

        listener.InstrumentPublished += (instrument, meterListener) =>
        {
            if (instrument.Meter.Name != "StellaOps.Policy.Gateway")
            {
                return;
            }

            meterListener.EnableMeasurementEvents(instrument);
        };

        listener.SetMeasurementEventCallback<long>((instrument, value, tags, _) =>
        {
            if (instrument.Name != "policy_gateway_activation_requests_total")
            {
                return;
            }

            activationMeasurements.Add((value, GetTag(tags, "outcome"), GetTag(tags, "source")));
        });

        listener.SetMeasurementEventCallback<double>((instrument, value, tags, _) =>
        {
            if (instrument.Name != "policy_gateway_activation_latency_ms")
            {
                return;
            }

            latencyMeasurements.Add((value, GetTag(tags, "outcome"), GetTag(tags, "source")));
        });

        listener.Start();

        using var client = factory.CreateClient();

        var response = await client.PostAsJsonAsync(
            "/api/policy/packs/example/revisions/3:activate",
            new ActivatePolicyRevisionRequest("upstream failure"));

        listener.Dispose();

        Assert.Equal(HttpStatusCode.BadGateway, response.StatusCode);

        Assert.Equal(1, tokenClient.RequestCount);

        var forwardedRequest = recordingHandler.LastRequest;
        Assert.NotNull(forwardedRequest);
        Assert.Equal("service-token", forwardedRequest!.Headers.Authorization?.Parameter);

        Assert.Contains(activationMeasurements, measurement =>
            measurement.Value == 1 &&
            measurement.Outcome == "error" &&
            measurement.Source == "service");

        Assert.Contains(latencyMeasurements, measurement =>
            measurement.Outcome == "error" &&
            measurement.Source == "service");
    }

    [Fact]
    public async Task ActivateRevision_RetriesOnTooManyRequests()
    {
        await using var factory = new PolicyGatewayWebApplicationFactory();

        var recordedDelays = new List<TimeSpan>();
        var originalSleep = SystemClock.SleepAsync;
        SystemClock.SleepAsync = (delay, cancellationToken) =>
        {
            recordedDelays.Add(delay);
            return Task.CompletedTask;
        };

        var tokenClient = factory.Services.GetRequiredService<StubTokenClient>();
        tokenClient.Reset();

        var recordingHandler = factory.Services.GetRequiredService<RecordingPolicyEngineHandler>();
        recordingHandler.Reset();
        recordingHandler.SetResponseSequence(new[]
        {
            CreateThrottleResponse(),
            CreateThrottleResponse(),
            RecordingPolicyEngineHandler.CreateSuccessResponse()
        });

        using var client = factory.CreateClient();

        try
        {
            var response = await client.PostAsJsonAsync(
                "/api/policy/packs/example/revisions/7:activate",
                new ActivatePolicyRevisionRequest("retry after throttle"));

            Assert.True(response.IsSuccessStatusCode, "Gateway should succeed after retrying throttled upstream responses.");
            Assert.Equal(1, tokenClient.RequestCount);
            Assert.Equal(3, recordingHandler.RequestCount);
        }
        finally
        {
            SystemClock.SleepAsync = originalSleep;
        }

        Assert.Equal(new[] { TimeSpan.FromSeconds(2), TimeSpan.FromSeconds(4) }, recordedDelays);
    }

    private static HttpResponseMessage CreateThrottleResponse()
    {
        var problem = new ProblemDetails
        {
            Title = "Too many requests",
            Detail = "Slow down.",
            Status = StatusCodes.Status429TooManyRequests
        };

        var response = new HttpResponseMessage((HttpStatusCode)StatusCodes.Status429TooManyRequests)
        {
            Content = JsonContent.Create(problem)
        };
        response.Headers.RetryAfter = new RetryConditionHeaderValue(TimeSpan.FromMilliseconds(10));
        return response;
    }

    private static string GetTag(ReadOnlySpan<KeyValuePair<string, object?>> tags, string key)
    {
        foreach (var tag in tags)
        {
            if (string.Equals(tag.Key, key, StringComparison.Ordinal))
            {
                return tag.Value?.ToString() ?? string.Empty;
            }
        }

        return string.Empty;
    }

    private sealed class PolicyGatewayWebApplicationFactory : WebApplicationFactory<Program>
    {
        protected override void ConfigureWebHost(IWebHostBuilder builder)
        {
            builder.UseEnvironment("Development");

            builder.ConfigureAppConfiguration((_, configurationBuilder) =>
            {
                var settings = new Dictionary<string, string?>
                {
                    ["PolicyGateway:Telemetry:MinimumLogLevel"] = "Warning",
                    ["PolicyGateway:ResourceServer:Authority"] = "https://authority.test",
                    ["PolicyGateway:ResourceServer:RequireHttpsMetadata"] = "false",
                    ["PolicyGateway:ResourceServer:BypassNetworks:0"] = "127.0.0.1/32",
                    ["PolicyGateway:ResourceServer:BypassNetworks:1"] = "::1/128",
                    ["PolicyGateway:PolicyEngine:BaseAddress"] = "https://policy-engine.test/",
                    ["PolicyGateway:PolicyEngine:ClientCredentials:Enabled"] = "true",
                    ["PolicyGateway:PolicyEngine:ClientCredentials:ClientId"] = "policy-gateway",
                    ["PolicyGateway:PolicyEngine:ClientCredentials:ClientSecret"] = "secret",
                    ["PolicyGateway:PolicyEngine:ClientCredentials:Scopes:0"] = "policy:activate",
                    ["PolicyGateway:PolicyEngine:Dpop:Enabled"] = "false"
                };

                configurationBuilder.AddInMemoryCollection(settings);
            });

            builder.ConfigureServices(services =>
            {
                services.RemoveAll<IStellaOpsTokenClient>();
                services.AddSingleton<StubTokenClient>();
                services.AddSingleton<IStellaOpsTokenClient>(sp => sp.GetRequiredService<StubTokenClient>());

                services.RemoveAll<PolicyEngineClient>();
                services.RemoveAll<IPolicyEngineClient>();
                services.AddSingleton<RecordingPolicyEngineHandler>();
                services.AddHttpClient<IPolicyEngineClient, PolicyEngineClient>()
                    .ConfigureHttpClient(client =>
                    {
                        client.BaseAddress = new Uri("https://policy-engine.test/");
                    })
                    .ConfigurePrimaryHttpMessageHandler(sp => sp.GetRequiredService<RecordingPolicyEngineHandler>());

                services.AddSingleton<IStartupFilter>(new RemoteIpStartupFilter());

                services.PostConfigure<JwtBearerOptions>(StellaOpsAuthenticationDefaults.AuthenticationScheme, options =>
                {
                    options.RequireHttpsMetadata = false;
                    options.Configuration = new OpenIdConnectConfiguration
                    {
                        Issuer = "https://authority.test",
                        TokenEndpoint = "https://authority.test/token"
                    };
                    options.TokenValidationParameters = new TokenValidationParameters
                    {
                        ValidateIssuer = false,
                        ValidateAudience = false,
                        ValidateIssuerSigningKey = false,
                        SignatureValidator = (token, parameters) => new JsonWebToken(token)
                    };
                    options.BackchannelHttpHandler = new NoOpBackchannelHandler();
                });

            });
        }
    }

    private sealed class RemoteIpStartupFilter : IStartupFilter
    {
        public Action<IApplicationBuilder> Configure(Action<IApplicationBuilder> next)
        {
            return app =>
            {
                app.Use(async (context, innerNext) =>
                {
                    context.Connection.RemoteIpAddress ??= IPAddress.Loopback;
                    await innerNext();
                });

                next(app);
            };
        }
    }

    private sealed class RecordingPolicyEngineHandler : HttpMessageHandler
    {
        private static readonly JsonSerializerOptions SerializerOptions = new(JsonSerializerDefaults.Web);

        public HttpRequestMessage? LastRequest { get; private set; }
        public int RequestCount { get; private set; }
        private Func<HttpRequestMessage, HttpResponseMessage>? responseFactory;
        private Queue<HttpResponseMessage>? responseQueue;

        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
        {
            LastRequest = request;
            RequestCount++;

            if (responseQueue is { Count: > 0 })
            {
                return Task.FromResult(responseQueue.Dequeue());
            }

            var response = responseFactory is not null
                ? responseFactory(request)
                : CreateSuccessResponse();

            return Task.FromResult(response);
        }

        public void Reset()
        {
            LastRequest = null;
            RequestCount = 0;
            responseFactory = null;
            responseQueue?.Clear();
            responseQueue = null;
        }

        public void SetResponseFactory(Func<HttpRequestMessage, HttpResponseMessage>? factory)
        {
            responseFactory = factory;
        }

        public void SetResponseSequence(IEnumerable<HttpResponseMessage> responses)
        {
            responseQueue = new Queue<HttpResponseMessage>(responses ?? Array.Empty<HttpResponseMessage>());
        }

        public static HttpResponseMessage CreateSuccessResponse()
        {
            var now = DateTimeOffset.UtcNow;
            var payload = new PolicyRevisionActivationDto(
                "activated",
                new PolicyRevisionDto(
                    5,
                    "activated",
                    false,
                    now,
                    now,
                    Array.Empty<PolicyActivationApprovalDto>()));

            return new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = JsonContent.Create(payload, options: SerializerOptions)
            };
        }
    }

    private sealed class NoOpBackchannelHandler : HttpMessageHandler
    {
        protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
            => Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK));
    }

    private sealed class StubTokenClient : IStellaOpsTokenClient
    {
        public int RequestCount { get; private set; }

        public void Reset()
        {
            RequestCount = 0;
        }

        public Task<StellaOpsTokenResult> RequestClientCredentialsTokenAsync(string? scope = null, IReadOnlyDictionary<string, string>? additionalParameters = null, CancellationToken cancellationToken = default)
        {
            RequestCount++;
            var expiresAt = DateTimeOffset.UtcNow.AddMinutes(5);
            return Task.FromResult(new StellaOpsTokenResult("service-token", "Bearer", expiresAt, Array.Empty<string>()));
        }

        public Task<StellaOpsTokenResult> RequestPasswordTokenAsync(string username, string password, string? scope = null, IReadOnlyDictionary<string, string>? additionalParameters = null, CancellationToken cancellationToken = default)
            => throw new NotSupportedException();

        public Task<JsonWebKeySet> GetJsonWebKeySetAsync(CancellationToken cancellationToken = default)
            => throw new NotSupportedException();

        public ValueTask<StellaOpsTokenCacheEntry?> GetCachedTokenAsync(string key, CancellationToken cancellationToken = default)
            => ValueTask.FromResult<StellaOpsTokenCacheEntry?>(null);

        public ValueTask CacheTokenAsync(string key, StellaOpsTokenCacheEntry entry, CancellationToken cancellationToken = default)
            => ValueTask.CompletedTask;

        public ValueTask ClearCachedTokenAsync(string key, CancellationToken cancellationToken = default)
            => ValueTask.CompletedTask;
    }
}