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

import 'package:halkyon_base_server/base.dart';
import 'package:mailer/mailer.dart' as mailer;
import 'package:mailer/smtp_server.dart';
import 'package:serverpod/serverpod.dart';
import 'package:test/test.dart';

/// An SMTP server on a loopback port that takes one mail at a time, offers
/// no TLS, and keeps what it is told.
final class _FakeSmtp {
  _FakeSmtp._(this._socket) {
    _socket.listen(_serve);
  }

  static Future<_FakeSmtp> start() async =>
      _FakeSmtp._(await ServerSocket.bind(InternetAddress.loopbackIPv4, 0));

  final ServerSocket _socket;

  /// The commands received, in order.
  final commands = <String>[];

  /// What each mail's DATA held, its lines joined.
  final mails = <String>[];

  int get port => _socket.port;

  Future<void> close() => _socket.close();

  void _serve(Socket client) {
    client.write('220 fake ESMTP\r\n');
    var step = '';
    final data = StringBuffer();
    utf8.decoder.bind(client).transform(const LineSplitter()).listen((line) {
      if (step == 'data') {
        if (line == '.') {
          step = '';
          mails.add(data.toString());
          data.clear();
          client.write('250 2.0.0 queued\r\n');
        } else {
          data.writeln(line);
        }
        return;
      }
      if (step == 'auth') {
        step = '';
        client.write('235 2.7.0 Authentication successful\r\n');
        return;
      }
      commands.add(line);
      final command = line.toUpperCase();
      if (command.startsWith('EHLO')) {
        client.write('250-fake\r\n250 AUTH PLAIN\r\n');
      } else if (command == 'AUTH PLAIN') {
        step = 'auth';
        client.write('334 \r\n');
      } else if (command == 'DATA') {
        step = 'data';
        client.write('354 End data with <CR><LF>.<CR><LF>\r\n');
      } else if (command == 'QUIT') {
        client
          ..write('221 2.0.0 Bye\r\n')
          ..close();
      } else {
        client.write('250 2.0.0 OK\r\n');
      }
    });
  }
}

/// The text of [mail] as DATA held it: its headers and its body, decoded
/// from base64 where it was encoded so.
({String headers, String body}) _read(String mail) {
  final at = mail.indexOf('\n\n');
  final headers = mail.substring(0, at);
  final body = mail.substring(at + 2);
  return (
    headers: headers,
    body: headers.toLowerCase().contains('content-transfer-encoding: base64')
        ? utf8.decode(base64.decode(body.replaceAll(RegExp(r'\s'), '')))
        : body,
  );
}

void main() {
  group('the mail', () {
    test('is plain text with the code first, in the subject too, naming '
        'the instance and how long the code lasts', () {
      final mail = codeMail(
        code: 'K7QX-M2PD',
        language: 'en',
        app: 'Halkyon Learn',
        instance: 'learn.halkyon.eu',
        purpose: EmailCodePurpose.signUp,
      );

      expect(
        mail.subject,
        'K7QX-M2PD: your Halkyon Learn code to create an account or give it '
        'a password',
      );
      expect(mail.body, startsWith('K7QX-M2PD\n\n'));
      expect(mail.body, contains('create your account on learn.halkyon.eu'));
      expect(mail.body, contains('15 minutes'));
      expect(mail.body, isNot(contains('http')));
    });

    test('says what its code would do, and to type it nowhere but the app '
        'on the instance, in each language', () {
      ({String subject, String body}) mailFor(
        EmailCodePurpose purpose,
        String language,
      ) => codeMail(
        code: 'K7QX-M2PD',
        language: language,
        app: 'Halkyon Learn',
        instance: 'learn.halkyon.eu',
        purpose: purpose,
      );
      const english = {
        EmailCodePurpose.signUp: 'to create your account',
        EmailCodePurpose.finishSetup: 'to finish setting up your account',
        EmailCodePurpose.authenticatorReset:
            "to switch off your authenticator app's codes",
        EmailCodePurpose.accountReset: 'to reset your account',
        EmailCodePurpose.deletion: 'to delete your account',
        EmailCodePurpose.firstPassword:
            'to give your account on learn.halkyon.eu its first password',
        EmailCodePurpose.joinSpace:
            'to join, with your account on learn.halkyon.eu, what this '
            'address was invited to',
      };
      const german = {
        EmailCodePurpose.signUp: 'um dein Konto auf learn.halkyon.eu anzulegen',
        EmailCodePurpose.finishSetup: 'um die Einrichtung deines Kontos',
        EmailCodePurpose.authenticatorReset:
            'um die Codes deiner Authenticator-App',
        EmailCodePurpose.accountReset: 'zurückzusetzen',
        EmailCodePurpose.deletion: 'mit allem darin zu löschen',
        EmailCodePurpose.firstPassword:
            'um deinem Konto auf learn.halkyon.eu sein erstes Passwort zu '
            'geben',
        EmailCodePurpose.joinSpace:
            'um mit deinem Konto auf learn.halkyon.eu dem beizutreten, wozu '
            'diese Adresse eingeladen wurde',
      };
      for (final purpose in EmailCodePurpose.values) {
        final en = mailFor(purpose, 'en').body;
        expect(en, contains(english[purpose]));
        expect(
          en,
          contains('Type it only in Halkyon Learn on learn.halkyon.eu'),
        );
        expect(en, isNot(contains('sign in')));
        final de = mailFor(purpose, 'de').body;
        expect(de, contains(german[purpose]));
        expect(
          de,
          contains('Gib ihn nur in Halkyon Learn auf learn.halkyon.eu'),
        );
      }
      expect(
        mailFor(EmailCodePurpose.accountReset, 'en').body,
        contains('what was encrypted with the old ones is lost'),
      );
    });

    test('names its purpose in the subject, which a notification shows '
        'alone (the third reading)', () {
      String subjectOf(EmailCodePurpose purpose, String language) => codeMail(
        code: 'K7QX-M2PD',
        language: language,
        app: 'Halkyon Learn',
        instance: 'learn.halkyon.eu',
        purpose: purpose,
      ).subject;
      const english = {
        EmailCodePurpose.signUp:
            'K7QX-M2PD: your Halkyon Learn code to create an account or give '
            'it a password',
        EmailCodePurpose.finishSetup:
            'K7QX-M2PD: your Halkyon Learn code to finish setting up your '
            'account',
        EmailCodePurpose.authenticatorReset:
            'K7QX-M2PD: your Halkyon Learn code to switch off your '
            'authenticator',
        EmailCodePurpose.accountReset:
            'K7QX-M2PD: your Halkyon Learn code to reset your account',
        EmailCodePurpose.deletion:
            'K7QX-M2PD: your Halkyon Learn code to delete your account',
        EmailCodePurpose.firstPassword:
            'K7QX-M2PD: your Halkyon Learn code to give your account a '
            'password',
        EmailCodePurpose.joinSpace:
            'K7QX-M2PD: your Halkyon Learn code to accept an invitation',
      };
      const german = {
        EmailCodePurpose.signUp:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um ein Konto anzulegen oder '
            'ihm ein Passwort zu geben',
        EmailCodePurpose.finishSetup:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um dein Konto fertig '
            'einzurichten',
        EmailCodePurpose.authenticatorReset:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um deine Authenticator-App '
            'abzuschalten',
        EmailCodePurpose.accountReset:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um dein Konto zurückzusetzen',
        EmailCodePurpose.deletion:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um dein Konto zu löschen',
        EmailCodePurpose.firstPassword:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um deinem Konto ein Passwort '
            'zu geben',
        EmailCodePurpose.joinSpace:
            'K7QX-M2PD: dein Halkyon-Learn-Code, um einer Einladung zu folgen',
      };
      for (final purpose in EmailCodePurpose.values) {
        expect(subjectOf(purpose, 'en'), english[purpose]);
        expect(subjectOf(purpose, 'de'), german[purpose]);
      }
    });

    test('for signing up, says it also gives a password to an account with '
        'that address and none yet', () {
      ({String subject, String body}) mailIn(String language) => codeMail(
        code: 'K7QX-M2PD',
        language: language,
        app: 'Halkyon Learn',
        instance: 'learn.halkyon.eu',
        purpose: EmailCodePurpose.signUp,
      );

      expect(
        mailIn('en').body,
        contains(
          'or, should an account there have this address and no password '
          'yet, to give it one',
        ),
      );
      expect(
        mailIn('de').body,
        contains(
          'oder, hat dort schon ein Konto diese Adresse und noch kein '
          'Passwort, ihm eines zu geben',
        ),
      );
    });

    test('in German for German, in English for anything else', () {
      ({String subject, String body}) mailIn(String language) => codeMail(
        code: 'K7QX-M2PD',
        language: language,
        app: 'Halkyon Learn',
        instance: 'x',
        purpose: EmailCodePurpose.signUp,
      );

      expect(
        mailIn('de').subject,
        'K7QX-M2PD: dein Halkyon-Learn-Code, um ein Konto anzulegen oder ihm '
        'ein Passwort zu geben',
      );
      expect(
        mailIn('fr').subject,
        'K7QX-M2PD: your Halkyon Learn code to create an account or give '
        'it a password',
      );
    });

    test('names the app the host is, in its text too', () {
      ({String subject, String body}) mailIn(String language) => codeMail(
        code: 'K7QX-M2PD',
        language: language,
        app: 'Halkyon Todo',
        instance: 'todo.example.org',
        purpose: EmailCodePurpose.signUp,
      );

      expect(
        mailIn('en').subject,
        'K7QX-M2PD: your Halkyon Todo code to create an account or give it a '
        'password',
      );
      expect(mailIn('en').body, contains('Type this code in Halkyon Todo'));
      expect(
        mailIn('de').subject,
        'K7QX-M2PD: dein Halkyon-Todo-Code, um ein Konto anzulegen oder '
        'ihm ein Passwort zu geben',
      );
      expect(mailIn('de').body, contains('Gib diesen Code in Halkyon Todo'));
    });
  });

  group("a reset's notice", () {
    ({String subject, String body}) notice(
      AccountResetKind kind,
      String language,
    ) => resetMail(
      kind: kind,
      takesEffectAt: DateTime.utc(2026, 10, 23, 14, 5, 59),
      language: language,
      app: 'Halkyon Learn',
      instance: 'learn.halkyon.eu',
    );

    test('says what goes when, in UTC, on which instance, and that signing '
        'in calls it off, in German for German and English else', () {
      for (final kind in AccountResetKind.values) {
        for (final language in ['en', 'de', 'fr']) {
          final mail = notice(kind, language);
          expect(mail.body, contains('2026-10-23 14:05 UTC'));
          expect(mail.body, contains('learn.halkyon.eu'));
          expect(mail.subject, contains('Halkyon Learn'));
          expect(
            mail.body,
            language == 'de'
                ? contains('bricht es ab')
                : contains('calls it off'),
          );
        }
      }
      expect(
        notice(AccountResetKind.account, 'en').body,
        contains('can no longer be read'),
      );
    });

    test('holds no link and no code: it helps nobody but the owner', () {
      for (final kind in AccountResetKind.values) {
        final mail = notice(kind, 'en');
        expect(mail.body, isNot(contains('http')));
        expect(mail.body, isNot(matches(RegExp('[0-9A-Z]{4}-[0-9A-Z]{4}'))));
      }
    });
  });

  group('codes go', () {
    final smtp = SmtpCodeMailer(
      server: SmtpServer('localhost'),
      from: const mailer.Address('learn@halkyon.eu'),
      app: 'Halkyon Learn',
      instance: 'learn.halkyon.eu',
    );

    test('through the SMTP service set up, in every run mode', () {
      for (final runMode in [
        ServerpodRunMode.development,
        ServerpodRunMode.production,
      ]) {
        expect(codeMailerFor(runMode: runMode, smtp: smtp), same(smtp));
      }
    });

    test('into the log in development without one, and nowhere elsewhere '
        '(no email sign-in)', () {
      expect(
        codeMailerFor(runMode: ServerpodRunMode.development, smtp: null),
        isA<LogCodeMailer>(),
      );
      for (final runMode in [
        ServerpodRunMode.staging,
        ServerpodRunMode.production,
        ServerpodRunMode.test,
      ]) {
        expect(codeMailerFor(runMode: runMode, smtp: null), isNull);
      }
    });
  });

  group('over SMTP', () {
    late _FakeSmtp server;

    setUp(() async => server = await _FakeSmtp.start());
    tearDown(() => server.close());

    SmtpCodeMailer mailerFor({required bool allowInsecure}) => SmtpCodeMailer(
      server: SmtpServer(
        '127.0.0.1',
        port: server.port,
        username: 'learn@halkyon.eu',
        password: 'token',
        allowInsecure: allowInsecure,
      ),
      from: const mailer.Address('learn@halkyon.eu', 'Halkyon Learn'),
      app: 'Halkyon Learn',
      instance: 'learn.halkyon.eu',
    );

    test(
      'mails the code from the address set up to the address typed',
      () async {
        await mailerFor(allowInsecure: true).mail(
          to: 'anna@example.org',
          code: 'K7QX-M2PD',
          language: 'de',
          purpose: EmailCodePurpose.signUp,
        );

        expect(server.commands, contains('MAIL FROM:<learn@halkyon.eu>'));
        expect(server.commands, contains('RCPT TO:<anna@example.org>'));
        final mail = _read(server.mails.single);
        expect(mail.headers, contains('Halkyon Learn'));
        expect(mail.headers, contains('<learn@halkyon.eu>'));
        expect(mail.headers, contains('text/plain'));
        expect(mail.body, startsWith('K7QX-M2PD'));
        expect(
          mail.body,
          contains('um dein Konto auf learn.halkyon.eu anzulegen'),
        );
      },
    );

    test('never over a connection without TLS', () async {
      await expectLater(
        mailerFor(allowInsecure: false).mail(
          to: 'anna@example.org',
          code: 'K7QX-M2PD',
          language: 'en',
          purpose: EmailCodePurpose.signUp,
        ),
        throwsA(isA<Exception>()),
      );
      expect(server.mails, isEmpty);
      expect(
        server.commands.where((command) => command.startsWith('AUTH')),
        isEmpty,
      );
    });
  });

  test('an invitation names who invites and where, its link and when it '
      'lapses, that joining takes a code mailed here, and nothing of what is '
      'shared, in each language', () {
    for (final language in ['en', 'de']) {
      final mail = invitationMail(
        inviter: 'Alice (@alice)',
        app: 'Halkyon Learn',
        link: Uri.parse('https://learn.halkyon.eu/join/abc'),
        lapsesAt: DateTime.utc(2026, 11, 25, 12),
        language: language,
      );
      expect(mail.subject, contains('Alice (@alice)'));
      expect(mail.subject, contains('Halkyon Learn'));
      expect(mail.body, contains('https://learn.halkyon.eu/join/abc'));
      expect(mail.body, contains('learn.halkyon.eu.'));
      expect(mail.body, contains('2026-11-25 12:00 UTC'));
      expect(
        mail.body,
        contains(language == 'de' ? 'einen Code' : 'mails a code'),
      );
    }
  });
}