using System.Reflection;
using FinalFactory.Rendezvous.Contracts;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;

namespace FinalFactory.Rendezvous.Server.Diagnostics;

internal static class DiagnosticDashboardEndpoints
{
    private const string ContentSecurityPolicy =
        "default-src 'none'; base-uri 'none'; connect-src 'self'; "
        + "font-src 'self'; form-action 'none'; frame-ancestors 'none'; "
        + "img-src 'self'; manifest-src 'none'; object-src 'none'; "
        + "script-src 'self'; style-src 'self'";
    private static readonly byte[] Index = ReadAsset("index.html");
    private static readonly byte[] Script = ReadAsset("app.mjs");
    private static readonly byte[] Styles = ReadAsset("styles.css");

    public static IEndpointRouteBuilder MapDiagnosticDashboardEndpoints(
        this IEndpointRouteBuilder endpoints)
    {
        RouteGroupBuilder dashboard = endpoints.MapGroup("/diagnostics")
            .ExcludeFromDescription();
        dashboard.MapGet("", ServeIndex);
        dashboard.MapGet("/app.mjs", ServeScript);
        dashboard.MapGet("/styles.css", ServeStyles);
        dashboard.MapGet("/config.json", ServeConfiguration);
        return endpoints;
    }

    private static IResult ServeIndex(
        HttpContext context,
        [FromServices] IOptions<DiagnosticDashboardOptions> configured) =>
        ServeAsset(context, configured.Value, Index, "text/html; charset=utf-8");

    private static IResult ServeScript(
        HttpContext context,
        [FromServices] IOptions<DiagnosticDashboardOptions> configured) =>
        ServeAsset(context, configured.Value, Script, "text/javascript; charset=utf-8");

    private static IResult ServeStyles(
        HttpContext context,
        [FromServices] IOptions<DiagnosticDashboardOptions> configured) =>
        ServeAsset(context, configured.Value, Styles, "text/css; charset=utf-8");

    private static IResult ServeConfiguration(
        HttpContext context,
        [FromServices] IOptions<DiagnosticDashboardOptions> configured)
    {
        DiagnosticDashboardOptions options = configured.Value;
        if (!options.Enabled)
        {
            return Results.NotFound();
        }

        ApplySecurityHeaders(context.Response);
        return Results.Json(new
        {
            contractVersion = ContractLimits.ContractVersion,
            pollIntervalSeconds = options.PollIntervalSeconds,
            maximumRenderedSessions = options.MaximumRenderedSessions,
            scopes = options.Scopes.Select(static scope => new
            {
                gameId = scope.GameId,
                environmentId = scope.EnvironmentId,
                protocolVersions = scope.ProtocolVersions,
                regions = scope.Regions,
                visibility = "public",
            }),
        });
    }

    private static IResult ServeAsset(
        HttpContext context,
        DiagnosticDashboardOptions options,
        byte[] content,
        string contentType)
    {
        if (!options.Enabled)
        {
            return Results.NotFound();
        }

        ApplySecurityHeaders(context.Response);
        return Results.Bytes(content, contentType);
    }

    private static void ApplySecurityHeaders(HttpResponse response)
    {
        response.Headers.CacheControl = "no-store";
        response.Headers["Content-Security-Policy"] = ContentSecurityPolicy;
        response.Headers["X-Content-Type-Options"] = "nosniff";
        response.Headers["X-Frame-Options"] = "DENY";
        response.Headers["Cross-Origin-Opener-Policy"] = "same-origin";
        response.Headers["Cross-Origin-Resource-Policy"] = "same-origin";
        response.Headers["Permissions-Policy"] =
            "camera=(), geolocation=(), microphone=(), payment=(), usb=()";
        response.Headers["Referrer-Policy"] = "no-referrer";
    }

    private static byte[] ReadAsset(string fileName)
    {
        Assembly assembly = typeof(DiagnosticDashboardEndpoints).Assembly;
        string resourceName = $"FinalFactory.Rendezvous.Server.Diagnostics.Assets.{fileName}";
        using Stream source = assembly.GetManifestResourceStream(resourceName)
            ?? throw new InvalidOperationException($"Missing embedded dashboard asset {fileName}.");
        using MemoryStream destination = new();
        source.CopyTo(destination);
        return destination.ToArray();
    }
}