using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Authentication;
using System.Security.Cryptography;
using System.Security.Claims;
using System.Security.Cryptography.X509Certificates;
using System.Threading.RateLimiting;
using Serilog;
using Serilog.Events;
using StellaOps.Attestor.Core.Options;
using StellaOps.Attestor.Core.Submission;
using StellaOps.Attestor.Infrastructure;
using StellaOps.Configuration;
using StellaOps.Auth.ServerIntegration;
using Microsoft.Extensions.Diagnostics.HealthChecks;
using OpenTelemetry.Metrics;
using StellaOps.Attestor.Core.Observability;
using StellaOps.Attestor.Core.Verification;
using Microsoft.AspNetCore.Server.Kestrel.Https;
using Serilog.Context;

const string ConfigurationSection = "attestor";

var builder = WebApplication.CreateBuilder(args);

builder.Configuration.AddStellaOpsDefaults(options =>
{
    options.BasePath = builder.Environment.ContentRootPath;
    options.EnvironmentPrefix = "ATTESTOR_";
    options.BindingSection = ConfigurationSection;
});

builder.Host.UseSerilog((context, services, loggerConfiguration) =>
{
    loggerConfiguration
        .MinimumLevel.Information()
        .MinimumLevel.Override("Microsoft", LogEventLevel.Warning)
        .Enrich.FromLogContext()
        .WriteTo.Console();
});

var attestorOptions = builder.Configuration.BindOptions<AttestorOptions>(ConfigurationSection);

var clientCertificateAuthorities = LoadClientCertificateAuthorities(attestorOptions.Security.Mtls.CaBundle);

builder.Services.AddSingleton(TimeProvider.System);
builder.Services.AddSingleton(attestorOptions);

builder.Services.AddRateLimiter(options =>
{
    options.RejectionStatusCode = StatusCodes.Status429TooManyRequests;
    options.OnRejected = static (context, _) =>
    {
        context.HttpContext.Response.Headers.TryAdd("Retry-After", "1");
        return ValueTask.CompletedTask;
    };

    options.AddPolicy("attestor-submissions", httpContext =>
    {
        var identity = httpContext.Connection.ClientCertificate?.Thumbprint
            ?? httpContext.User.FindFirst("sub")?.Value
            ?? httpContext.User.FindFirst("client_id")?.Value
            ?? httpContext.Connection.RemoteIpAddress?.ToString()
            ?? "anonymous";

        var quota = attestorOptions.Quotas.PerCaller;
        var tokensPerPeriod = Math.Max(1, quota.Qps);
        var tokenLimit = Math.Max(tokensPerPeriod, quota.Burst);
        var queueLimit = Math.Max(quota.Burst, tokensPerPeriod);

        return RateLimitPartition.GetTokenBucketLimiter(identity, _ => new TokenBucketRateLimiterOptions
        {
            TokenLimit = tokenLimit,
            TokensPerPeriod = tokensPerPeriod,
            ReplenishmentPeriod = TimeSpan.FromSeconds(1),
            QueueLimit = queueLimit,
            QueueProcessingOrder = QueueProcessingOrder.OldestFirst,
            AutoReplenishment = true
        });
    });
});

builder.Services.AddOptions<AttestorOptions>()
    .Bind(builder.Configuration.GetSection(ConfigurationSection))
    .ValidateOnStart();

builder.Services.AddProblemDetails();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddAttestorInfrastructure();
builder.Services.AddHttpContextAccessor();
builder.Services.AddHealthChecks()
    .AddCheck("self", () => HealthCheckResult.Healthy());

builder.Services.AddOpenTelemetry()
    .WithMetrics(metricsBuilder =>
    {
        metricsBuilder.AddMeter(AttestorMetrics.MeterName);
        metricsBuilder.AddAspNetCoreInstrumentation();
        metricsBuilder.AddRuntimeInstrumentation();
    });

if (attestorOptions.Security.Authority is { Issuer: not null } authority)
{
    builder.Services.AddStellaOpsResourceServerAuthentication(
        builder.Configuration,
        configurationSection: null,
        configure: resourceOptions =>
        {
            resourceOptions.Authority = authority.Issuer!;
            resourceOptions.RequireHttpsMetadata = authority.RequireHttpsMetadata;
            if (!string.IsNullOrWhiteSpace(authority.JwksUrl))
            {
                resourceOptions.MetadataAddress = authority.JwksUrl;
            }

            foreach (var audience in authority.Audiences)
            {
                resourceOptions.Audiences.Add(audience);
            }

            foreach (var scope in authority.RequiredScopes)
            {
                resourceOptions.RequiredScopes.Add(scope);
            }
        });

    builder.Services.AddAuthorization(options =>
    {
        options.AddPolicy("attestor:write", policy =>
        {
            policy.RequireAuthenticatedUser();
            policy.RequireClaim("scope", authority.RequiredScopes);
        });
    });
}
else
{
    builder.Services.AddAuthorization();
}

builder.WebHost.ConfigureKestrel(kestrel =>
{
    kestrel.ConfigureHttpsDefaults(https =>
    {
        if (attestorOptions.Security.Mtls.RequireClientCertificate)
        {
            https.ClientCertificateMode = ClientCertificateMode.RequireCertificate;
        }

        https.SslProtocols = SslProtocols.Tls13 | SslProtocols.Tls12;

        https.ClientCertificateValidation = (certificate, _, _) =>
        {
            if (!attestorOptions.Security.Mtls.RequireClientCertificate)
            {
                return true;
            }

            if (certificate is null)
            {
                Log.Warning("Client certificate missing");
                return false;
            }

            if (clientCertificateAuthorities.Count > 0)
            {
                using var chain = new X509Chain
                {
                    ChainPolicy =
                    {
                        RevocationMode = X509RevocationMode.NoCheck,
                        TrustMode = X509ChainTrustMode.CustomRootTrust
                    }
                };

                foreach (var authority in clientCertificateAuthorities)
                {
                    chain.ChainPolicy.CustomTrustStore.Add(authority);
                }

                if (!chain.Build(certificate))
                {
                    Log.Warning("Client certificate chain validation failed for {Subject}", certificate.Subject);
                    return false;
                }
            }

            if (attestorOptions.Security.Mtls.AllowedThumbprints.Count > 0 &&
                !attestorOptions.Security.Mtls.AllowedThumbprints.Contains(certificate.Thumbprint ?? string.Empty, StringComparer.OrdinalIgnoreCase))
            {
                Log.Warning("Client certificate thumbprint {Thumbprint} rejected", certificate.Thumbprint);
                return false;
            }

            if (attestorOptions.Security.Mtls.AllowedSubjects.Count > 0 &&
                !attestorOptions.Security.Mtls.AllowedSubjects.Contains(certificate.Subject, StringComparer.OrdinalIgnoreCase))
            {
                Log.Warning("Client certificate subject {Subject} rejected", certificate.Subject);
                return false;
            }

            return true;
        };
    });
});

var app = builder.Build();

app.UseSerilogRequestLogging();

app.Use(async (context, next) =>
{
    var correlationId = context.Request.Headers["X-Correlation-Id"].FirstOrDefault();
    if (string.IsNullOrWhiteSpace(correlationId))
    {
        correlationId = Guid.NewGuid().ToString("N");
    }

    context.Response.Headers["X-Correlation-Id"] = correlationId;

    using (LogContext.PushProperty("CorrelationId", correlationId))
    {
        await next().ConfigureAwait(false);
    }
});

app.UseExceptionHandler(static handler =>
{
    handler.Run(async context =>
    {
        var result = Results.Problem(statusCode: StatusCodes.Status500InternalServerError);
        await result.ExecuteAsync(context);
    });
});

app.UseRateLimiter();

app.UseAuthentication();
app.UseAuthorization();

app.MapHealthChecks("/health/ready");
app.MapHealthChecks("/health/live");

app.MapPost("/api/v1/rekor/entries", async (AttestorSubmissionRequest request, HttpContext httpContext, IAttestorSubmissionService submissionService, CancellationToken cancellationToken) =>
{
    var certificate = httpContext.Connection.ClientCertificate;
    if (certificate is null)
    {
        return Results.Problem(statusCode: StatusCodes.Status403Forbidden, title: "Client certificate required");
    }

    var user = httpContext.User;
    if (user?.Identity is not { IsAuthenticated: true })
    {
        return Results.Problem(statusCode: StatusCodes.Status401Unauthorized, title: "Authentication required");
    }

    var submissionContext = BuildSubmissionContext(user, certificate);

    try
    {
        var result = await submissionService.SubmitAsync(request, submissionContext, cancellationToken).ConfigureAwait(false);
        return Results.Ok(result);
    }
    catch (AttestorValidationException validationEx)
    {
        return Results.Problem(statusCode: StatusCodes.Status400BadRequest, title: validationEx.Message, extensions: new Dictionary<string, object?>
        {
            ["code"] = validationEx.Code
        });
    }
})
.RequireAuthorization("attestor:write")
.RequireRateLimiting("attestor-submissions");

app.MapGet("/api/v1/rekor/entries/{uuid}", async (string uuid, bool? refresh, IAttestorVerificationService verificationService, CancellationToken cancellationToken) =>
{
    var entry = await verificationService.GetEntryAsync(uuid, refresh is true, cancellationToken).ConfigureAwait(false);
    if (entry is null)
    {
        return Results.NotFound();
    }

    return Results.Ok(new
    {
        uuid = entry.RekorUuid,
        index = entry.Index,
        backend = entry.Log.Backend,
        proof = entry.Proof is null ? null : new
        {
            checkpoint = entry.Proof.Checkpoint is null ? null : new
            {
                origin = entry.Proof.Checkpoint.Origin,
                size = entry.Proof.Checkpoint.Size,
                rootHash = entry.Proof.Checkpoint.RootHash,
                timestamp = entry.Proof.Checkpoint.Timestamp?.ToString("O")
            },
            inclusion = entry.Proof.Inclusion is null ? null : new
            {
                leafHash = entry.Proof.Inclusion.LeafHash,
                path = entry.Proof.Inclusion.Path
            }
        },
        logURL = entry.Log.Url,
        status = entry.Status,
        mirror = entry.Mirror is null ? null : new
        {
            backend = entry.Mirror.Backend,
            uuid = entry.Mirror.Uuid,
            index = entry.Mirror.Index,
            logURL = entry.Mirror.Url,
            status = entry.Mirror.Status,
            proof = entry.Mirror.Proof is null ? null : new
            {
                checkpoint = entry.Mirror.Proof.Checkpoint is null ? null : new
                {
                    origin = entry.Mirror.Proof.Checkpoint.Origin,
                    size = entry.Mirror.Proof.Checkpoint.Size,
                    rootHash = entry.Mirror.Proof.Checkpoint.RootHash,
                    timestamp = entry.Mirror.Proof.Checkpoint.Timestamp?.ToString("O")
                },
                inclusion = entry.Mirror.Proof.Inclusion is null ? null : new
                {
                    leafHash = entry.Mirror.Proof.Inclusion.LeafHash,
                    path = entry.Mirror.Proof.Inclusion.Path
                }
            },
            error = entry.Mirror.Error
        },
        artifact = new
        {
            sha256 = entry.Artifact.Sha256,
            kind = entry.Artifact.Kind,
            imageDigest = entry.Artifact.ImageDigest,
            subjectUri = entry.Artifact.SubjectUri
        }
    });
}).RequireAuthorization("attestor:write");

app.MapPost("/api/v1/rekor/verify", async (AttestorVerificationRequest request, IAttestorVerificationService verificationService, CancellationToken cancellationToken) =>
{
    try
    {
        var result = await verificationService.VerifyAsync(request, cancellationToken).ConfigureAwait(false);
        return Results.Ok(result);
    }
    catch (AttestorVerificationException ex)
    {
        return Results.Problem(statusCode: StatusCodes.Status400BadRequest, title: ex.Message, extensions: new Dictionary<string, object?>
        {
            ["code"] = ex.Code
        });
    }
}).RequireAuthorization("attestor:write");

app.Run();

static SubmissionContext BuildSubmissionContext(ClaimsPrincipal user, X509Certificate2 certificate)
{
    var subject = user.FindFirst("sub")?.Value ?? certificate.Subject;
    var audience = user.FindFirst("aud")?.Value ?? string.Empty;
    var clientId = user.FindFirst("client_id")?.Value;
    var tenant = user.FindFirst("tenant")?.Value;

    return new SubmissionContext
    {
        CallerSubject = subject,
        CallerAudience = audience,
        CallerClientId = clientId,
        CallerTenant = tenant,
        ClientCertificate = certificate,
        MtlsThumbprint = certificate.Thumbprint
    };
}

static List<X509Certificate2> LoadClientCertificateAuthorities(string? path)
{
    var certificates = new List<X509Certificate2>();

    if (string.IsNullOrWhiteSpace(path))
    {
        return certificates;
    }

    try
    {
        if (!File.Exists(path))
        {
            Log.Warning("Client CA bundle '{Path}' not found", path);
            return certificates;
        }

        var collection = new X509Certificate2Collection();
        collection.ImportFromPemFile(path);

        certificates.AddRange(collection.Cast<X509Certificate2>());
    }
    catch (Exception ex) when (ex is IOException or CryptographicException)
    {
        Log.Warning(ex, "Failed to load client CA bundle from {Path}", path);
    }

    return certificates;
}