Github = {};

OAuth.registerService('github', 2, null, async (query) => {
  const accessToken = await getAccessToken(query);
  const identity = await getIdentity(accessToken);
  const emails = await getEmails(accessToken);
  const primaryEmail = emails.find((email) => email.primary);

  return {
    serviceData: {
      id: identity.id,
      accessToken: OAuth.sealSecret(accessToken),
      email: identity.email || (primaryEmail && primaryEmail.email) || '',
      username: identity.login,
      name: identity.name,
      avatar: identity.avatar_url,
      company: identity.company,
      blog: identity.blog,
      location: identity.location,
      bio: identity.bio,
      emails
    },
    options: { profile: { name: identity.name } }
  };
});

// http://developer.github.com/v3/#user-agent-required
let userAgent = 'Meteor';
if (Meteor.release) userAgent += `/${Meteor.release}`;

const getAccessToken = async (query) => {
  const config = ServiceConfiguration.configurations.findOne({
    service: 'github'
  });
  if (!config) throw new ServiceConfiguration.ConfigError();

  let response;
  try {
    const content = new URLSearchParams({
      client_id: config.clientId,
      client_secret: config.secret,
      code: query.code,
      redirect_uri: OAuth._redirectUri(
        'github',
        config
      )
    });
    const request = await fetch(
      `https://github.com/login/oauth/access_token?${content.toString()}`,
      {
        method: 'POST',
        headers: {
          Accept: 'application/json',
          'User-Agent': userAgent
        }
      }
    );
    response = await request.json();
  } catch (err) {
    throw Object.assign(
      new Error(
        `Failed to complete OAuth handshake with Github. ${err.message}`
      ),
      { response: err.response }
    );
  }
  if (response.error) {
    // if the http response was a json object with an error attribute
    throw new Error(
      `Failed to complete OAuth handshake with GitHub. ${response.error}`
    );
  } else {
    return response.access_token;
  }
};

const getIdentity = async (accessToken) => {
  try {
    const request = await fetch('https://api.github.com/user', {
      method: 'GET',
      headers: {
        Accept: 'application/json',
        'User-Agent': userAgent,
        Authorization: `token ${accessToken}`
      } // http://developer.github.com/v3/#user-agent-required
    });
    return await request.json();
  } catch (err) {
    throw Object.assign(
      new Error(`Failed to fetch identity from Github. ${err.message}`),
      { response: err.response }
    );
  }
};

const getEmails = async (accessToken) => {
  try {
    const request = await fetch('https://api.github.com/user/emails', {
      method: 'GET',
      headers: {
        'User-Agent': userAgent,
        Accept: 'application/json',
        Authorization: `token ${accessToken}`
      } // http://developer.github.com/v3/#user-agent-required
    });
    return await request.json();
  } catch (err) {
    return [];
  }
};

Github.retrieveCredential = (credentialToken, credentialSecret) =>
  OAuth.retrieveCredential(credentialToken, credentialSecret);