// Copyright 2022 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

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

import 'package:github/github.dart';
import 'package:shelf/shelf.dart';
import 'package:crypto/crypto.dart';

import '../request_handling/pubsub.dart';
import '../service/config.dart';
import '../service/log.dart';
import '../server/request_handler.dart';
import '../requests/exceptions.dart';

/// Handler for processing GitHub webhooks.
///
/// On events where an 'autosubmit' label was added to a pull request,
/// check if the pull request is mergable and publish to pubsub.
class GithubWebhook extends RequestHandler {
  const GithubWebhook({
    required Config config,
    this.pubsub = const PubSub(),
  }) : super(config: config);

  final PubSub pubsub;

  @override
  Future<Response> post(Request request) async {
    final Map<String, String> reqHeader = request.headers;
    log.info('Header: $reqHeader');

    final String? gitHubEvent = request.headers['X-GitHub-Event'];

    if (gitHubEvent == null || request.headers['X-Hub-Signature'] == null) {
      throw const BadRequestException('Missing required headers.');
    }
    final List<int> requestBytes = await request.read().expand((_) => _).toList();
    final String? hmacSignature = request.headers['X-Hub-Signature'];
    if (!await _validateRequest(hmacSignature, requestBytes)) {
      throw const Forbidden();
    }

    // Listen to the pull request with 'autosubmit' label.
    bool hasAutosubmit = false;
    final String rawBody = utf8.decode(requestBytes);
    final body = json.decode(rawBody) as Map<String, dynamic>;

    if (!body.containsKey('pull_request') || !((body['pull_request'] as Map<String, dynamic>).containsKey('labels'))) {
      return Response.ok(jsonEncode(<String, String>{}));
    }

    final PullRequest pullRequest = PullRequest.fromJson(body['pull_request'] as Map<String, dynamic>);
    hasAutosubmit = pullRequest.labels!.any((label) => label.name == config.autosubmitLabel);

    if (hasAutosubmit) {
      log.info('Found pull request with auto submit label.');
      await pubsub.publish('auto-submit-queue', pullRequest);
    }

    return Response.ok(rawBody);
  }

  Future<bool> _validateRequest(
    String? signature,
    List<int> requestBody,
  ) async {
    final String rawKey = await config.getWebhookKey();
    final List<int> key = utf8.encode(rawKey);
    final Hmac hmac = Hmac(sha1, key);
    final Digest digest = hmac.convert(requestBody);
    final String bodySignature = 'sha1=$digest';
    return bodySignature == signature;
  }
}