Ghost/ghost/email-service/lib/mailgun-email-provider.js

const logging = require('@tryghost/logging');
const errors = require('@tryghost/errors');
const debug = require('@tryghost/debug')('email-service:mailgun-provider-service');

/**
 * @typedef {object} Recipient
 * @prop {string} email
 * @prop {Replacement[]} replacements
 */

/**
 * @typedef {object} Replacement
 * @prop {string} token
 * @prop {string} value
 * @prop {string} id
 */

/**
 * @typedef {object} EmailSendingOptions
 * @prop {boolean} clickTrackingEnabled
 * @prop {boolean} openTrackingEnabled
 */

/**
 * @typedef {object} EmailProviderSuccessResponse
 * @prop {string} id
 */

class MailgunEmailProvider {
    #mailgunClient;
    #errorHandler;

    static BATCH_SIZE = 1000;

    /**
     * @param {object} dependencies
     * @param {import('@tryghost/mailgun-client/lib/mailgun-client')} dependencies.mailgunClient - mailgun client to send emails
     * @param {Function} [dependencies.errorHandler] - custom error handler for logging exceptions
     */
    constructor({
        mailgunClient,
        errorHandler
    }) {
        this.#mailgunClient = mailgunClient;
        this.#errorHandler = errorHandler;
    }

    #createRecipientData(replacements) {
        let recipientData = {};

        recipientData = replacements.reduce((acc, replacement) => {
            const {id, value} = replacement;
            if (!acc[id]) {
                acc[id] = {};
            }
            acc[id] = value;
            return acc;
        }, {});

        return recipientData;
    }

    #updateRecipientVariables(data, replacementDefinitions) {
        for (const def of replacementDefinitions) {
            data = data.replace(
                def.token,
                `%recipient.${def.id}%`
            );
        }
        return data;
    }

    /**
     * Create mailgun error message for storing in the database
     * @param {Object} error
     * @param {string} error.message
     * @param {string} error.details
     * @returns {string}
    */
    #createMailgunErrorMessage(error) {
        const message = (error?.message || '') + ':' + (error?.details || '');
        return message.slice(0, 2000);
    }

    /**
     * Send an email using the Mailgun API
     * @param {import('./sending-service').EmailData} data
     * @param {EmailSendingOptions} options
     * @returns {Promise<EmailProviderSuccessResponse>}
    */
    async send(data, options) {
        const {
            subject,
            html,
            plaintext,
            from,
            replyTo,
            emailId,
            recipients,
            replacementDefinitions
        } = data;

        logging.info(`Sending email to ${recipients.length} recipients`);
        const startTime = Date.now();
        debug(`sending message to ${recipients.length} recipients`);

        try {
            const messageData = {
                subject,
                html,
                plaintext,
                from,
                replyTo,
                id: emailId,
                track_opens: !!options.openTrackingEnabled,
                track_clicks: !!options.clickTrackingEnabled
            };

            // create recipient data for Mailgun using replacement definitions
            const recipientData = recipients.reduce((acc, recipient) => {
                acc[recipient.email] = this.#createRecipientData(recipient.replacements);
                return acc;
            }, {});

            // update content to use Mailgun variable syntax for all replacements
            ['html', 'plaintext'].forEach((key) => {
                if (messageData[key]) {
                    messageData[key] = this.#updateRecipientVariables(messageData[key], replacementDefinitions);
                }
            });

            // send the email using Mailgun
            // uses empty replacements array as we've already replaced all tokens with Mailgun variables
            const response = await this.#mailgunClient.send(
                messageData,
                recipientData,
                []
            );

            debug(`sent message (${Date.now() - startTime}ms)`);
            logging.info(`Sent message (${Date.now() - startTime}ms)`);

            // Return mailgun provider id, trim <> from response
            return {
                id: response.id.trim().replace(/^<|>$/g, '')
            };
        } catch (e) {
            let ghostError;
            if (e.error && e.messageData) {
                const {error, messageData} = e;
                
                // REF: possible mailgun errors https://documentation.mailgun.com/en/latest/api-intro.html#status-codes
                ghostError = new errors.EmailError({
                    statusCode: error.status,
                    message: this.#createMailgunErrorMessage(error),
                    errorDetails: JSON.stringify({error, messageData}),
                    context: `Mailgun Error ${error.status}: ${error.details}`,
                    help: `https://ghost.org/docs/newsletters/#bulk-email-configuration`,
                    code: 'BULK_EMAIL_SEND_FAILED'
                });
            } else {
                ghostError = new errors.EmailError({
                    statusCode: undefined,
                    message: e.message,
                    errorDetails: undefined,
                    context: e.context || 'Mailgun Error',
                    code: 'BULK_EMAIL_SEND_FAILED'
                });
            }

            logging.warn(ghostError);
            debug(`failed to send message (${Date.now() - startTime}ms)`);

            // log error to custom error handler. ex sentry
            this.#errorHandler(ghostError);
            throw ghostError;
        }
    }

    getMaximumRecipients() {
        return MailgunEmailProvider.BATCH_SIZE;
    }
}

module.exports = MailgunEmailProvider;