using System;
using System.Diagnostics;
using System.IO;
using System.Net.Http;
using System.Net;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using NetEscapades.Configuration.Yaml;
using StellaOps.Auth.Abstractions;
using StellaOps.Auth.Client;
using StellaOps.Auth.ServerIntegration;
using StellaOps.Configuration;
using StellaOps.Policy.Gateway.Clients;
using StellaOps.Policy.Gateway.Contracts;
using StellaOps.Policy.Gateway.Infrastructure;
using StellaOps.Policy.Gateway.Options;
using StellaOps.Policy.Gateway.Services;
using Polly;
using Polly.Extensions.Http;
using StellaOps.AirGap.Policy;

var builder = WebApplication.CreateBuilder(args);

builder.Logging.ClearProviders();
builder.Logging.AddJsonConsole();

builder.Configuration.AddStellaOpsDefaults(options =>
{
    options.BasePath = builder.Environment.ContentRootPath;
    options.EnvironmentPrefix = "STELLAOPS_POLICY_GATEWAY_";
    options.ConfigureBuilder = configurationBuilder =>
    {
        var contentRoot = builder.Environment.ContentRootPath;
        foreach (var relative in new[]
        {
            "../etc/policy-gateway.yaml",
            "../etc/policy-gateway.local.yaml",
            "policy-gateway.yaml",
            "policy-gateway.local.yaml"
        })
        {
            var path = Path.Combine(contentRoot, relative);
            configurationBuilder.AddYamlFile(path, optional: true);
        }
    };
});

var bootstrap = StellaOpsConfigurationBootstrapper.Build<PolicyGatewayOptions>(options =>
{
    options.BasePath = builder.Environment.ContentRootPath;
    options.EnvironmentPrefix = "STELLAOPS_POLICY_GATEWAY_";
    options.BindingSection = PolicyGatewayOptions.SectionName;
    options.ConfigureBuilder = configurationBuilder =>
    {
        foreach (var relative in new[]
        {
            "../etc/policy-gateway.yaml",
            "../etc/policy-gateway.local.yaml",
            "policy-gateway.yaml",
            "policy-gateway.local.yaml"
        })
        {
            var path = Path.Combine(builder.Environment.ContentRootPath, relative);
            configurationBuilder.AddYamlFile(path, optional: true);
        }
    };
    options.PostBind = static (value, _) => value.Validate();
});

builder.Configuration.AddConfiguration(bootstrap.Configuration);

builder.Services.AddAirGapEgressPolicy(builder.Configuration, sectionName: "AirGap");

builder.Logging.SetMinimumLevel(bootstrap.Options.Telemetry.MinimumLogLevel);

builder.Services.AddOptions<PolicyGatewayOptions>()
    .Bind(builder.Configuration.GetSection(PolicyGatewayOptions.SectionName))
    .Validate(options =>
    {
        try
        {
            options.Validate();
            return true;
        }
        catch (Exception ex)
        {
            throw new OptionsValidationException(
                PolicyGatewayOptions.SectionName,
                typeof(PolicyGatewayOptions),
                new[] { ex.Message });
        }
    })
    .ValidateOnStart();

builder.Services.AddSingleton(sp => sp.GetRequiredService<IOptions<PolicyGatewayOptions>>().Value);
builder.Services.AddSingleton(TimeProvider.System);
builder.Services.AddRouting(options => options.LowercaseUrls = true);
builder.Services.AddProblemDetails();
builder.Services.AddHealthChecks();
builder.Services.AddAuthentication();
builder.Services.AddAuthorization();
builder.Services.AddStellaOpsScopeHandler();
builder.Services.AddStellaOpsResourceServerAuthentication(
    builder.Configuration,
    configurationSection: $"{PolicyGatewayOptions.SectionName}:ResourceServer");
builder.Services.AddSingleton<PolicyGatewayMetrics>();
builder.Services.AddSingleton<PolicyGatewayDpopProofGenerator>();
builder.Services.AddSingleton<PolicyEngineTokenProvider>();
builder.Services.AddTransient<PolicyGatewayDpopHandler>();

if (bootstrap.Options.PolicyEngine.ClientCredentials.Enabled)
{
    builder.Services.AddOptions<StellaOpsAuthClientOptions>()
        .Configure(options =>
        {
            options.Authority = bootstrap.Options.ResourceServer.Authority;
            options.ClientId = bootstrap.Options.PolicyEngine.ClientCredentials.ClientId;
            options.ClientSecret = bootstrap.Options.PolicyEngine.ClientCredentials.ClientSecret;
            options.HttpTimeout = TimeSpan.FromSeconds(bootstrap.Options.PolicyEngine.ClientCredentials.BackchannelTimeoutSeconds);
            foreach (var scope in bootstrap.Options.PolicyEngine.ClientCredentials.Scopes)
            {
                options.DefaultScopes.Add(scope);
            }
        })
        .PostConfigure(static opt => opt.Validate());

    builder.Services.TryAddSingleton<IStellaOpsTokenCache, InMemoryTokenCache>();

    builder.Services.AddHttpClient<StellaOpsDiscoveryCache>((provider, client) =>
    {
        var authOptions = provider.GetRequiredService<IOptionsMonitor<StellaOpsAuthClientOptions>>().CurrentValue;
        client.Timeout = authOptions.HttpTimeout;
    }).AddPolicyHandler(static (provider, _) => CreateAuthorityRetryPolicy(provider));

    builder.Services.AddHttpClient<StellaOpsJwksCache>((provider, client) =>
    {
        var authOptions = provider.GetRequiredService<IOptionsMonitor<StellaOpsAuthClientOptions>>().CurrentValue;
        client.Timeout = authOptions.HttpTimeout;
    }).AddPolicyHandler(static (provider, _) => CreateAuthorityRetryPolicy(provider));

    builder.Services.AddHttpClient<IStellaOpsTokenClient, StellaOpsTokenClient>((provider, client) =>
    {
        var authOptions = provider.GetRequiredService<IOptionsMonitor<StellaOpsAuthClientOptions>>().CurrentValue;
        client.Timeout = authOptions.HttpTimeout;
    })
    .AddPolicyHandler(static (provider, _) => CreateAuthorityRetryPolicy(provider))
    .AddHttpMessageHandler<PolicyGatewayDpopHandler>();
}

builder.Services.AddHttpClient<IPolicyEngineClient, PolicyEngineClient>((serviceProvider, client) =>
{
    var gatewayOptions = serviceProvider.GetRequiredService<IOptions<PolicyGatewayOptions>>().Value;
    var egressPolicy = serviceProvider.GetService<IEgressPolicy>();
    if (egressPolicy is not null)
    {
        egressPolicy.EnsureAllowed(new EgressRequest("PolicyGateway", gatewayOptions.PolicyEngine.BaseUri, "policy-engine-client"));
    }
    client.BaseAddress = gatewayOptions.PolicyEngine.BaseUri;
    client.Timeout = TimeSpan.FromSeconds(gatewayOptions.PolicyEngine.ClientCredentials.BackchannelTimeoutSeconds);
})
.AddPolicyHandler(static (provider, _) => CreatePolicyEngineRetryPolicy(provider));

var app = builder.Build();

app.UseExceptionHandler(static appBuilder => appBuilder.Run(async context =>
{
    context.Response.StatusCode = StatusCodes.Status500InternalServerError;
    await context.Response.WriteAsJsonAsync(new { error = "Unexpected gateway error." });
}));

app.UseStatusCodePages();

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

app.MapHealthChecks("/healthz");

app.MapGet("/readyz", () => Results.Ok(new { status = "ready" }))
    .WithName("Readiness");

app.MapGet("/", () => Results.Redirect("/healthz"));

var policyPacks = app.MapGroup("/api/policy/packs")
    .WithTags("Policy Packs");

policyPacks.MapGet(string.Empty, async Task<IResult> (
        HttpContext context,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.ListPolicyPacksAsync(forwardingContext, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRead));

policyPacks.MapPost(string.Empty, async Task<IResult> (
        HttpContext context,
        CreatePolicyPackRequest request,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        if (request is null)
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Request body required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.CreatePolicyPackAsync(forwardingContext, request, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyAuthor));

policyPacks.MapPost("/{packId}/revisions", async Task<IResult> (
        HttpContext context,
        string packId,
        CreatePolicyRevisionRequest request,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        if (string.IsNullOrWhiteSpace(packId))
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "packId is required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        if (request is null)
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Request body required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.CreatePolicyRevisionAsync(forwardingContext, packId, request, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyAuthor));

policyPacks.MapPost("/{packId}/revisions/{version:int}:activate", async Task<IResult> (
        HttpContext context,
        string packId,
        int version,
        ActivatePolicyRevisionRequest request,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        PolicyGatewayMetrics metrics,
        ILoggerFactory loggerFactory,
        CancellationToken cancellationToken) =>
    {
        if (string.IsNullOrWhiteSpace(packId))
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "packId is required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        if (request is null)
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Request body required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        GatewayForwardingContext? forwardingContext = null;
        var source = "service";
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
            source = "caller";
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var stopwatch = System.Diagnostics.Stopwatch.StartNew();
        var response = await client.ActivatePolicyRevisionAsync(forwardingContext, packId, version, request, cancellationToken).ConfigureAwait(false);
        stopwatch.Stop();

        var outcome = DetermineActivationOutcome(response);
        metrics.RecordActivation(outcome, source, stopwatch.Elapsed.TotalMilliseconds);

        var logger = loggerFactory.CreateLogger("StellaOps.Policy.Gateway.Activation");
        LogActivation(logger, packId, version, outcome, source, response.StatusCode);

        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(
        StellaOpsScopes.PolicyOperate,
        StellaOpsScopes.PolicyActivate));

var cvss = app.MapGroup("/api/cvss")
    .WithTags("CVSS Receipts");

cvss.MapPost("/receipts", async Task<IResult>(
        HttpContext context,
        CreateCvssReceiptRequest request,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        if (request is null)
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Request body required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.CreateCvssReceiptAsync(forwardingContext, request, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRun));

cvss.MapGet("/receipts/{receiptId}", async Task<IResult>(
        HttpContext context,
        string receiptId,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.GetCvssReceiptAsync(forwardingContext, receiptId, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.FindingsRead));

cvss.MapPut("/receipts/{receiptId}/amend", async Task<IResult>(
        HttpContext context,
        string receiptId,
        AmendCvssReceiptRequest request,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        if (request is null)
        {
            return Results.BadRequest(new ProblemDetails
            {
                Title = "Request body required.",
                Status = StatusCodes.Status400BadRequest
            });
        }

        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.AmendCvssReceiptAsync(forwardingContext, receiptId, request, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.PolicyRun));

cvss.MapGet("/receipts/{receiptId}/history", async Task<IResult>(
        HttpContext context,
        string receiptId,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.GetCvssReceiptHistoryAsync(forwardingContext, receiptId, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.FindingsRead));

cvss.MapGet("/policies", async Task<IResult>(
        HttpContext context,
        IPolicyEngineClient client,
        PolicyEngineTokenProvider tokenProvider,
        CancellationToken cancellationToken) =>
    {
        GatewayForwardingContext? forwardingContext = null;
        if (GatewayForwardingContext.TryCreate(context, out var callerContext))
        {
            forwardingContext = callerContext;
        }
        else if (!tokenProvider.IsEnabled)
        {
            return Results.Unauthorized();
        }

        var response = await client.ListCvssPoliciesAsync(forwardingContext, cancellationToken).ConfigureAwait(false);
        return response.ToMinimalResult();
    })
    .RequireAuthorization(policy => policy.RequireStellaOpsScopes(StellaOpsScopes.FindingsRead));

app.Run();

static IAsyncPolicy<HttpResponseMessage> CreateAuthorityRetryPolicy(IServiceProvider provider)
{
    var authOptions = provider.GetRequiredService<IOptionsMonitor<StellaOpsAuthClientOptions>>().CurrentValue;
    var delays = authOptions.NormalizedRetryDelays;
    if (delays.Count == 0)
    {
        return Policy.NoOpAsync<HttpResponseMessage>();
    }

    var loggerFactory = provider.GetService<ILoggerFactory>();
    var logger = loggerFactory?.CreateLogger("PolicyGateway.AuthorityHttp");

    return HttpPolicyExtensions
        .HandleTransientHttpError()
        .OrResult(static message => message.StatusCode == HttpStatusCode.TooManyRequests)
        .WaitAndRetryAsync(
            delays.Count,
            attempt => delays[attempt - 1],
            (outcome, delay, attempt, _) =>
            {
                logger?.LogWarning(
                    outcome.Exception,
                    "Retrying Authority HTTP call ({Attempt}/{Total}) after {Reason}; waiting {Delay}.",
                    attempt,
                    delays.Count,
                    outcome.Exception?.Message ?? outcome.Result?.StatusCode.ToString(),
                    delay);
            });
}

static IAsyncPolicy<HttpResponseMessage> CreatePolicyEngineRetryPolicy(IServiceProvider provider)
    => HttpPolicyExtensions
        .HandleTransientHttpError()
        .OrResult(static response => response.StatusCode is HttpStatusCode.TooManyRequests or HttpStatusCode.BadGateway or HttpStatusCode.ServiceUnavailable or HttpStatusCode.GatewayTimeout)
        .WaitAndRetryAsync(3, attempt => TimeSpan.FromSeconds(Math.Pow(2, attempt)));

static string DetermineActivationOutcome(PolicyEngineResponse<PolicyRevisionActivationDto> response)
{
    if (response.IsSuccess)
    {
        return response.Value?.Status switch
        {
            "activated" => "activated",
            "already_active" => "already_active",
            "pending_second_approval" => "pending_second_approval",
            _ => "success"
        };
    }

    return response.StatusCode switch
    {
        HttpStatusCode.BadRequest => "bad_request",
        HttpStatusCode.NotFound => "not_found",
        HttpStatusCode.Unauthorized => "unauthorized",
        HttpStatusCode.Forbidden => "forbidden",
        _ => "error"
    };
}

static void LogActivation(ILogger logger, string packId, int version, string outcome, string source, HttpStatusCode statusCode)
{
    if (logger is null)
    {
        return;
    }

    var message = "Policy activation forwarded.";
    var logLevel = outcome is "activated" or "already_active" or "pending_second_approval" ? LogLevel.Information : LogLevel.Warning;
    logger.Log(logLevel, message + " Outcome={Outcome}; Source={Source}; PackId={PackId}; Version={Version}; StatusCode={StatusCode}.", outcome, source, packId, version, (int)statusCode);
}

public partial class Program
{
}