import 'dart:async';
import 'dart:convert';

import 'package:clock/clock.dart';
import 'package:halkyon_oidc_server/oidc.dart';
import 'package:http/http.dart' as http;
import 'package:http/testing.dart';

import 'test_provider.dart';

/// An OpenID Connect provider answering the module's requests in the test:
/// its discovery document, its keys, and its token endpoint, which gives an
/// ID token for a code it issued ([authorize]), signed with [key], for its
/// client alone.
final class FakeProvider {
  FakeProvider({
    required this.key,
    this.issuer = 'https://id.example',
    this.clientId = 'client-1',
    this.clientSecret = 'secret-1',
    this.pkce = true,
    this.discovered = false,
  });

  final TestKey key;
  final String issuer;
  final String clientId;
  final String clientSecret;
  final bool pkce;

  /// Whether the host reads its endpoints from its discovery document.
  final bool discovered;

  final callbackUrl = Uri.parse('https://app.example/oidc-callback');

  /// The codes it issued, each taken once: what its ID token says.
  final _codes = <String, _Code>{};

  /// What its token endpoint was asked, in order.
  final tokenRequests = <http.Request>[];

  /// How often its discovery document and its keys were fetched.
  int discoveries = 0;
  int keyFetches = 0;

  /// What its token endpoint answers instead of a token, for tests of its
  /// failures: a status (and body), or an error thrown.
  ({int status, String body})? tokenAnswer;
  Exception? tokenError;

  /// How long its token endpoint takes to answer.
  Duration tokenDelay = Duration.zero;

  /// What its discovery document says of its issuer, for a test of one
  /// naming another.
  String? discoveryIssuer;

  /// The provider as the host names it.
  OidcProvider get provider => OidcProvider(
    key: 'fake',
    issuer: issuer,
    clientId: clientId,
    clientSecret: clientSecret,
    callbackUrl: callbackUrl,
    pkce: pkce,
    scopes: const ['openid', 'profile'],
    endpoints: discovered
        ? null
        : OidcEndpoints(
            authorization: Uri.parse('$issuer/authorize'),
            token: Uri.parse('$issuer/token'),
            jwks: Uri.parse('$issuer/jwks'),
          ),
  );

  /// The person [subject] allowing the sign-in [authorizationUrl] asks for: the
  /// code the provider sends back, whose ID token carries the URL's nonce and
  /// [claims]; [nonce] in its place, for a test of a code of another attempt.
  String authorize(
    Uri authorizationUrl, {
    required String subject,
    Map<String, Object?> claims = const {},
    String? nonce,
  }) {
    final query = authorizationUrl.queryParameters;
    final code = randomText(24);
    _codes[code] = _Code(
      subject: subject,
      nonce: nonce ?? query['nonce']!,
      challenge: query['code_challenge'],
      claims: claims,
    );
    return code;
  }

  /// The HTTP client the module asks the provider through.
  http.Client get client => MockClient(_answer);

  Future<http.Response> _answer(http.Request request) async {
    final path = request.url.path;
    if (request.method == 'GET' &&
        path == '/.well-known/openid-configuration') {
      discoveries++;
      return http.Response(
        jsonEncode({
          'issuer': discoveryIssuer ?? issuer,
          'authorization_endpoint': '$issuer/authorize',
          'token_endpoint': '$issuer/token',
          'jwks_uri': '$issuer/jwks',
        }),
        200,
      );
    }
    if (request.method == 'GET' && path == '/jwks') {
      keyFetches++;
      return http.Response(jwksOf([key]), 200);
    }
    if (request.method == 'POST' && path == '/token') {
      tokenRequests.add(request);
      await Future<void>.delayed(tokenDelay);
      if (tokenError case final error?) {
        throw error;
      }
      if (tokenAnswer case (:final status, :final body)) {
        return http.Response(body, status);
      }
      return _token(request);
    }
    return http.Response('', 404);
  }

  http.Response _token(http.Request request) {
    final basic =
        'Basic ${base64.encode(utf8.encode('$clientId:$clientSecret'))}';
    final form = request.bodyFields;
    final code = _codes.remove(form['code']);
    if (request.headers['authorization'] != basic ||
        form['grant_type'] != 'authorization_code' ||
        form['redirect_uri'] != '$callbackUrl' ||
        code == null ||
        (code.challenge != null &&
            pkceChallenge(form['code_verifier'] ?? '') != code.challenge)) {
      return http.Response(jsonEncode({'error': 'invalid_grant'}), 400);
    }
    final now = clock.now();
    return http.Response(
      jsonEncode({
        'access_token': randomText(),
        'token_type': 'Bearer',
        'expires_in': 3600,
        'id_token': key.sign({
          'iss': issuer,
          'sub': code.subject,
          'aud': clientId,
          'exp': secondsOf(now.add(const Duration(hours: 1))),
          'iat': secondsOf(now),
          'nonce': code.nonce,
          ...code.claims,
        }),
      }),
      200,
      headers: {'content-type': 'application/json'},
    );
  }
}

final class _Code {
  _Code({
    required this.subject,
    required this.nonce,
    required this.challenge,
    required this.claims,
  });

  final String subject;
  final String nonce;
  final String? challenge;
  final Map<String, Object?> claims;
}