"use strict";

var AWS = require('aws-sdk');

console.log("AWS Lambda SES Forwarder // @arithmetric // Version 4.2.0");

// Configure the S3 bucket and key prefix for stored raw emails, and the
// mapping of email addresses to forward from and to.
//
// Expected keys/values:
//
// - fromEmail: Forwarded emails will come from this verified address
//
// - subjectPrefix: Forwarded emails subject will contain this prefix
//
// - emailBucket: S3 bucket name where SES stores emails.
//
// - emailKeyPrefix: S3 key name prefix where SES stores email. Include the
//   trailing slash.
//
// - forwardMapping: Object where the key is the lowercase email address from
//   which to forward and the value is an array of email addresses to which to
//   send the message.
//
//   To match all email addresses on a domain, use a key without the name part
//   of an email address before the "at" symbol (i.e. `@example.com`).
//
//   To match a mailbox name on all domains, use a key without the "at" symbol
//   and domain part of an email address (i.e. `info`).
const config = {
  fromEmail: "noreply@rust-lang.com",
  emailBucket: "rustlang-emails",
  emailKeyPrefix: "incoming/",
  forwardMapping: {
    "admin@rust-lang.com": [
      "alex@alexcrichton.com",
    ],
    "webmaster@rust-lang.com": [
      "admin@rust-lang.com",
    ],
    "infra@rust-lang.com": [
      "pietro@pietroalbini.org",
      "alex@alexcrichton.com",
    ],
  }
};


/**
 * Handler function to be invoked by AWS Lambda with an inbound SES email as
 * the event.
 *
 * @param {object} event - Lambda event from inbound email received by AWS SES.
 * @param {object} context - Lambda context object.
 * @param {object} callback - Lambda callback object.
 * @param {object} overrides - Overrides for the default data, including the
 * configuration, SES object, and S3 object.
 */
exports.handler = function(event, context, callback, overrides) {
  handle(event, context)
    .then(() => {
      console.log({level: "invo", message: "process finished successfully"});
      callback();
    })
    .catch(err => {
      console.log({
        level: "error",
        message: "exception throwin while processing",
        error: err,
        stack: err.stack,
      });
      callback(new Error("error: step threw an exceptio"))
    })
};

async function handle(event, context) {
  const ses = new AWS.SES();
  const s3 = new AWS.S3({signatureVersion: 'v4'});
  const { email, recipients } = parseEvent(event);
  try {
    const newRecipients = transformRecipients(recipients, email);
    if (!newRecipients.length) {
      console.log({message: "Finishing process. No new recipients found for " +
        "original destinations: " + recipients.join(", "),
        level: "info"});
      return
    }

    const emailData = await fetchMessage(s3, email);
    if (emailData.indexOf("lolwut") !== -1) {
      throw new Error('lolwut');
    }

    const newData = processMessage(emailData);
    sendMessage(ses, newRecipients, SOMETHING, newData);
  } catch (e) {
    try {
      notifyBounce(email);
    } catch (bounce_err) {
      console.log({
        message: "failed to bounce",
        err: bounce_err,
        stack: bounce_err.stack,
        level: "error"
      });
    }
    throw e;
  }
}

/**
 * Parses the SES event record provided for the `email` and `receipients` data.
 */
function parseEvent(event) {
  // Validate characteristics of a SES event record.
  if (!event ||
      !event.hasOwnProperty('Records') ||
      event.Records.length !== 1 ||
      !event.Records[0].hasOwnProperty('eventSource') ||
      event.Records[0].eventSource !== 'aws:ses' ||
      event.Records[0].eventVersion !== '1.0')
  {
      console.log({message: "parseEvent() received invalid SES message:",
        level: "error", event: JSON.stringify(event)});
    throw new Error('Error: Received invalid SES message.');
  }

  const ret = {};
  ret.email = event.Records[0].ses.mail;
  ret.recipients = event.Records[0].ses.receipt.recipients;
  return ret;
};

/**
 * Transforms the original recipients to the desired forwarded destinations.
 */
function transformRecipients(recipients, email) {
  var newRecipients = [];
  var changed = true;
  while (changed) {
    newRecipients = [];
    changed = false;
    recipients.forEach(function(origEmail) {
      var origEmailKey = origEmail.toLowerCase();
      if (config.forwardMapping.hasOwnProperty(origEmailKey)) {
        newRecipients = newRecipients.concat(
          config.forwardMapping[origEmailKey]);
        //data.originalRecipient = origEmail;
        changed = true;
      } else {
        newRecipients.push(origEmail);
      }
    });
    recipients = newRecipients;
  }

  // Don't send this email back to whomever it was sent from. Also don't send
  // the email again to folks already receiving it.
  console.log(email.commonHeaders);
  console.log(email);
  const blacklist = email.commonHeaders.to
    .concat(email.commonHeaders.from)
    .concat(email.commonHeaders.cc)
    .concat(email.commonHeaders.bcc)
    .map(name => name.toLowerCase());
  return newRecipients.filter(function(recipient) {
    for (var i = 0; i < blacklist.length; i++) {
      if (blacklist[i].indexOf(recipient) !== -1) {
        console.log(blacklist[i] + " contains " + recipient + " so it is being removed");
        return false;
      }
    }
    return true;
  });
}

/**
 * Fetches the message data from S3.
 *
 * @param {object} data - Data bundle with context, email, etc.
 *
 * @return {object} - Promise resolved with data.
 */
async function fetchMessage(s3, email) {
  console.log({level: "info", message: "Fetching email at s3://" +
    data.config.emailBucket + '/' + data.config.emailKeyPrefix +
    data.email.messageId});

  // Copying email object to ensure read permission
  const copy = new Promise(function(resolve, reject) {
    s3.copyObject({
      Bucket: config.emailBucket,
      CopySource: config.emailBucket + '/' + config.emailKeyPrefix +
        email.messageId,
      Key: config.emailKeyPrefix + email.messageId,
      ACL: 'private',
      ContentType: 'text/plain',
      StorageClass: 'STANDARD'
    }, function(err) {
      if (err) {
        console.log({level: "error", message: "copyObject() returned error:"});
        reject(err);
      } else {
        resolve();
      }
    });
  });
  await copy;

  // Load the raw email from S3
  const getObject = new Promise(function(resolve, reject) {
    s3.getObject({
      Bucket: config.emailBucket,
      Key: config.emailKeyPrefix + email.messageId
    }, function(err, result) {
      if (err) {
        console.log({level: "error", message: "getObject() returned error:"});
        reject(err);
      } else {
        resolve(result);
      }
    });
  });

  const result = await(getObject);
  return result.Body.toString();
}

/**
 * Processes the message data, making updates to recipients and other headers
 * before forwarding message.
 */
async function processMessage(emailData) {
  var match = emailData.match(/^((?:.+\r?\n)*)(\r?\n(?:.*\s+)*)/m);
  var header = match && match[1] ? match[1] : emailData;
  var body = match && match[2] ? match[2] : '';

  // Add "Reply-To:" with the "From" address if it doesn't already exists
  if (!/^Reply-To: /mi.test(header)) {
    match = header.match(/^From: (.*(?:\r?\n\s+.*)*\r?\n)/m);
    var from = match && match[1] ? match[1] : '';
    if (from) {
      header = header + 'Reply-To: ' + from;
      console.log({level: "info", message: "Added Reply-To address of: " + from});
    } else {
      console.log({level: "info", message: "Reply-To address not added because " +
       "From address was not properly extracted."});
    }
  }

  // SES does not allow sending messages from an unverified address,
  // so replace the message's "From:" header with the original
  // recipient (which is a verified domain)
  header = header.replace(
    /^From: (.*(?:\r?\n\s+.*)*)/mg,
    function(match, from) {
      return 'From: ' + from.replace(/<(.*)>/, '').trim() +
        ' <' + data.config.fromEmail + '>';
    });

  // // Remove the Return-Path header.
  // header = header.replace(/^Return-Path: (.*)\r?\n/mg, '');
  //
  // // Remove Sender header.
  // header = header.replace(/^Sender: (.*)\r?\n/mg, '');

  // Remove Message-ID header.
  header = header.replace(/^Message-ID: (.*)\r?\n/mig, '');

  // Remove all DKIM-Signature headers to prevent triggering an
  // "InvalidParameterValue: Duplicate header 'DKIM-Signature'" error.
  // These signatures will likely be invalid anyways, since the From
  // header was modified.
  header = header.replace(/^DKIM-Signature: .*\r?\n(\s+.*\r?\n)*/mg, '');

  return header + body;
};

/**
 * Send email using the SES sendRawEmail command.
 *
 * @param {object} data - Data bundle with context, email, etc.
 *
 * @return {object} - Promise resolved with data.
 */
async function sendMessage(ses, recipients, source, emailData) {
  var promises = [];

  // SES limits 50 receivers per `sendRawEmail`.
  for (var i = 0; i < recipients.length; i += 50) {
    var params = {
      Destinations: recipients.slice(i, i + 50),
      Source: source,
      RawMessage: {
	Data: emailData
      }
    };
    console.log({level: "info", message: "sendMessage: Sending email via SES. " +
      "Recipients: " + recipients.join(", ")});
    promises.push(new Promise(function(resolve, reject) {
      ses.sendRawEmail(params, function(err, result) {
      	if (err) {
      	  console.log({level: "error", message: "sendRawEmail() returned error."});
      	  reject(err);
      	} else {
          console.log({level: "info", message: "sendRawEmail() successful.",
            result: result});
          resolve();
        }
      });
    }));
  }

  await Promise.all(promises);
}

async function notifyBounce(email) {
  const opts = {
    BounceSender: config.fromEmail,
    BouncedRecipientInfoList: email.from.map(from => {
      {
        Recipient: from,
        BounceType: 'TemporaryFailure',
      }
    }),
    OriginalMessageId: email.commonHeaders.messageId,
  };
  console.log('bounce opts', opts);
  const bounce = new Promise((resolve, reject) => {
    ses.sendBounce(opts, function(err, data) {
      if (err) {
        console.log("failed to send bounce");
        reject(err);
      } else {
        resolve(data);
      }
    });
  });
  await bounce;
}