using StellaOps.Router.Common.Models;
using StellaOps.Router.Gateway;
using System.Text.Json;

namespace StellaOps.Gateway.WebService.Authorization;

public sealed class AuthorizationMiddleware
{
    private readonly RequestDelegate _next;
    private readonly IEffectiveClaimsStore _claimsStore;
    private readonly ILogger<AuthorizationMiddleware> _logger;

    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
        WriteIndented = false
    };

    public AuthorizationMiddleware(
        RequestDelegate next,
        IEffectiveClaimsStore claimsStore,
        ILogger<AuthorizationMiddleware> logger)
    {
        _next = next;
        _claimsStore = claimsStore;
        _logger = logger;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        if (!context.Items.TryGetValue(RouterHttpContextKeys.EndpointDescriptor, out var endpointObj) ||
            endpointObj is not EndpointDescriptor endpoint)
        {
            await _next(context);
            return;
        }

        if (endpoint.AllowAnonymous)
        {
            await _next(context);
            return;
        }

        var requiresAuthentication = EndpointAuthorizationSemantics.ResolveRequiresAuthentication(endpoint);
        var isAuthenticated = context.User.Identity?.IsAuthenticated == true;
        if (requiresAuthentication && !isAuthenticated)
        {
            _logger.LogWarning(
                "Authorization failed for {Method} {Path}: unauthenticated principal",
                endpoint.Method,
                endpoint.Path);

            await WriteUnauthorizedAsync(context, endpoint);
            return;
        }

        var effectiveClaims = _claimsStore.GetEffectiveClaims(
            endpoint.ServiceName,
            endpoint.Method,
            endpoint.Path);

        if (effectiveClaims.Count == 0)
        {
            await _next(context);
            return;
        }

        foreach (var required in effectiveClaims)
        {
            var userClaims = context.User.Claims;
            var hasClaim = required.Value == null
                ? userClaims.Any(c => c.Type == required.Type)
                : userClaims.Any(c => c.Type == required.Type && c.Value == required.Value);

            if (!hasClaim)
            {
                _logger.LogWarning(
                    "Authorization failed for {Method} {Path}: user lacks claim {ClaimType}={ClaimValue}",
                    endpoint.Method,
                    endpoint.Path,
                    required.Type,
                    required.Value ?? "(any)");

                await WriteForbiddenAsync(context, endpoint, required);
                return;
            }
        }

        await _next(context);
    }

    private static Task WriteUnauthorizedAsync(HttpContext context, EndpointDescriptor endpoint)
    {
        context.Response.StatusCode = StatusCodes.Status401Unauthorized;
        context.Response.ContentType = "application/json; charset=utf-8";

        var payload = new AuthorizationFailureResponse(
            Error: "unauthorized",
            Message: "Authentication required",
            RequiredClaimType: string.Empty,
            RequiredClaimValue: null,
            Service: endpoint.ServiceName,
            Version: endpoint.Version);

        return JsonSerializer.SerializeAsync(context.Response.Body, payload, JsonOptions, context.RequestAborted);
    }

    private static Task WriteForbiddenAsync(
        HttpContext context,
        EndpointDescriptor endpoint,
        ClaimRequirement required)
    {
        context.Response.StatusCode = StatusCodes.Status403Forbidden;
        context.Response.ContentType = "application/json; charset=utf-8";

        var payload = new AuthorizationFailureResponse(
            Error: "forbidden",
            Message: "Authorization failed: missing required claim",
            RequiredClaimType: required.Type,
            RequiredClaimValue: required.Value,
            Service: endpoint.ServiceName,
            Version: endpoint.Version);

        return JsonSerializer.SerializeAsync(context.Response.Body, payload, JsonOptions, context.RequestAborted);
    }

    private sealed record AuthorizationFailureResponse(
        string Error,
        string Message,
        string RequiredClaimType,
        string? RequiredClaimValue,
        string Service,
        string Version);
}