<?php

class Mandrill_Messages {
    public function __construct(Mandrill $master) {
        $this->master = $master;
    }

    /**
     * Send a new transactional message through Mandrill
     * @param struct $message the information on the message to send
     *     - html string the full HTML content to be sent
     *     - text string optional full text content to be sent
     *     - subject string the message subject
     *     - from_email string the sender email address.
     *     - from_name string optional from name to be used
     *     - to array an array of recipient information.
     *         - to[] struct a single recipient's information.
     *             - email string the email address of the recipient
     *             - name string the optional display name to use for the recipient
     *             - type string the header type to use for the recipient, defaults to "to" if not provided
     *     - headers struct optional extra headers to add to the message (most headers are allowed)
     *     - important boolean whether or not this message is important, and should be delivered ahead of non-important messages
     *     - track_opens boolean whether or not to turn on open tracking for the message
     *     - track_clicks boolean whether or not to turn on click tracking for the message
     *     - auto_text boolean whether or not to automatically generate a text part for messages that are not given text
     *     - auto_html boolean whether or not to automatically generate an HTML part for messages that are not given HTML
     *     - inline_css boolean whether or not to automatically inline all CSS styles provided in the message HTML - only for HTML documents less than 256KB in size
     *     - url_strip_qs boolean whether or not to strip the query string from URLs when aggregating tracked URL data
     *     - preserve_recipients boolean whether or not to expose all recipients in to "To" header for each email
     *     - view_content_link boolean set to false to remove content logging for sensitive emails
     *     - bcc_address string an optional address to receive an exact copy of each recipient's email
     *     - tracking_domain string a custom domain to use for tracking opens and clicks instead of mandrillapp.com
     *     - signing_domain string a custom domain to use for SPF/DKIM signing instead of mandrill (for "via" or "on behalf of" in email clients)
     *     - return_path_domain string a custom domain to use for the messages's return-path
     *     - merge boolean whether to evaluate merge tags in the message. Will automatically be set to true if either merge_vars or global_merge_vars are provided.
     *     - global_merge_vars array global merge variables to use for all recipients. You can override these per recipient.
     *         - global_merge_vars[] struct a single global merge variable
     *             - name string the global merge variable's name. Merge variable names are case-insensitive and may not start with _
     *             - content string the global merge variable's content
     *     - merge_vars array per-recipient merge variables, which override global merge variables with the same name.
     *         - merge_vars[] struct per-recipient merge variables
     *             - rcpt string the email address of the recipient that the merge variables should apply to
     *             - vars array the recipient's merge variables
     *                 - vars[] struct a single merge variable
     *                     - name string the merge variable's name. Merge variable names are case-insensitive and may not start with _
     *                     - content string the merge variable's content
     *     - tags array an array of string to tag the message with.  Stats are accumulated using tags, though we only store the first 100 we see, so this should not be unique or change frequently.  Tags should be 50 characters or less.  Any tags starting with an underscore are reserved for internal use and will cause errors.
     *         - tags[] string a single tag - must not start with an underscore
     *     - subaccount string the unique id of a subaccount for this message - must already exist or will fail with an error
     *     - google_analytics_domains array an array of strings indicating for which any matching URLs will automatically have Google Analytics parameters appended to their query string automatically.
     *     - google_analytics_campaign array|string optional string indicating the value to set for the utm_campaign tracking parameter. If this isn't provided the email's from address will be used instead.
     *     - metadata array metadata an associative array of user metadata. Mandrill will store this metadata and make it available for retrieval. In addition, you can select up to 10 metadata fields to index and make searchable using the Mandrill search api.
     *     - recipient_metadata array Per-recipient metadata that will override the global values specified in the metadata parameter.
     *         - recipient_metadata[] struct metadata for a single recipient
     *             - rcpt string the email address of the recipient that the metadata is associated with
     *             - values array an associated array containing the recipient's unique metadata. If a key exists in both the per-recipient metadata and the global metadata, the per-recipient metadata will be used.
     *     - attachments array an array of supported attachments to add to the message
     *         - attachments[] struct a single supported attachment
     *             - type string the MIME type of the attachment
     *             - name string the file name of the attachment
     *             - content string the content of the attachment as a base64-encoded string
     *     - images array an array of embedded images to add to the message
     *         - images[] struct a single embedded image
     *             - type string the MIME type of the image - must start with "image/"
     *             - name string the Content ID of the image - use <img src="cid:THIS_VALUE"> to reference the image in your HTML content
     *             - content string the content of the image as a base64-encoded string
     * @param boolean $async enable a background sending mode that is optimized for bulk sending. In async mode, messages/send will immediately return a status of "queued" for every recipient. To handle rejections when sending in async mode, set up a webhook for the 'reject' event. Defaults to false for messages with no more than 10 recipients; messages with more than 10 recipients are always sent asynchronously, regardless of the value of async.
     * @param string $ip_pool the name of the dedicated ip pool that should be used to send the message. If you do not have any dedicated IPs, this parameter has no effect. If you specify a pool that does not exist, your default pool will be used instead.
     * @param string $send_at when this message should be sent as a UTC timestamp in YYYY-MM-DD HH:MM:SS format. If you specify a time in the past, the message will be sent immediately. An additional fee applies for scheduled email, and this feature is only available to accounts with a positive balance.
     * @return array of structs for each recipient containing the key "email" with the email address, and details of the message status for that recipient
     *     - return[] struct the sending results for a single recipient
     *         - email string the email address of the recipient
     *         - status string the sending status of the recipient - either "sent", "queued", "scheduled", "rejected", or "invalid"
     *         - reject_reason string the reason for the rejection if the recipient status is "rejected" - one of "hard-bounce", "soft-bounce", "spam", "unsub", "custom", "invalid-sender", "invalid", "test-mode-limit", or "rule"
     *         - _id string the message's unique id
     */
    public function send($message, $async=false, $ip_pool=null, $send_at=null) {
        $_params = array("message" => $message, "async" => $async, "ip_pool" => $ip_pool, "send_at" => $send_at);
        return $this->master->call('messages/send', $_params);
    }

    /**
     * Send a new transactional message through Mandrill using a template
     * @param string $template_name the immutable name or slug of a template that exists in the user's account. For backwards-compatibility, the template name may also be used but the immutable slug is preferred.
     * @param array $template_content an array of template content to send.  Each item in the array should be a struct with two keys - name: the name of the content block to set the content for, and content: the actual content to put into the block
     *     - template_content[] struct the injection of a single piece of content into a single editable region
     *         - name string the name of the mc:edit editable region to inject into
     *         - content string the content to inject
     * @param struct $message the other information on the message to send - same as /messages/send, but without the html content
     *     - html string optional full HTML content to be sent if not in template
     *     - text string optional full text content to be sent
     *     - subject string the message subject
     *     - from_email string the sender email address.
     *     - from_name string optional from name to be used
     *     - to array an array of recipient information.
     *         - to[] struct a single recipient's information.
     *             - email string the email address of the recipient
     *             - name string the optional display name to use for the recipient
     *             - type string the header type to use for the recipient, defaults to "to" if not provided
     *     - headers struct optional extra headers to add to the message (most headers are allowed)
     *     - important boolean whether or not this message is important, and should be delivered ahead of non-important messages
     *     - track_opens boolean whether or not to turn on open tracking for the message
     *     - track_clicks boolean whether or not to turn on click tracking for the message
     *     - auto_text boolean whether or not to automatically generate a text part for messages that are not given text
     *     - auto_html boolean whether or not to automatically generate an HTML part for messages that are not given HTML
     *     - inline_css boolean whether or not to automatically inline all CSS styles provided in the message HTML - only for HTML documents less than 256KB in size
     *     - url_strip_qs boolean whether or not to strip the query string from URLs when aggregating tracked URL data
     *     - preserve_recipients boolean whether or not to expose all recipients in to "To" header for each email
     *     - view_content_link boolean set to false to remove content logging for sensitive emails
     *     - bcc_address string an optional address to receive an exact copy of each recipient's email
     *     - tracking_domain string a custom domain to use for tracking opens and clicks instead of mandrillapp.com
     *     - signing_domain string a custom domain to use for SPF/DKIM signing instead of mandrill (for "via" or "on behalf of" in email clients)
     *     - return_path_domain string a custom domain to use for the messages's return-path
     *     - merge boolean whether to evaluate merge tags in the message. Will automatically be set to true if either merge_vars or global_merge_vars are provided.
     *     - global_merge_vars array global merge variables to use for all recipients. You can override these per recipient.
     *         - global_merge_vars[] struct a single global merge variable
     *             - name string the global merge variable's name. Merge variable names are case-insensitive and may not start with _
     *             - content string the global merge variable's content
     *     - merge_vars array per-recipient merge variables, which override global merge variables with the same name.
     *         - merge_vars[] struct per-recipient merge variables
     *             - rcpt string the email address of the recipient that the merge variables should apply to
     *             - vars array the recipient's merge variables
     *                 - vars[] struct a single merge variable
     *                     - name string the merge variable's name. Merge variable names are case-insensitive and may not start with _
     *                     - content string the merge variable's content
     *     - tags array an array of string to tag the message with.  Stats are accumulated using tags, though we only store the first 100 we see, so this should not be unique or change frequently.  Tags should be 50 characters or less.  Any tags starting with an underscore are reserved for internal use and will cause errors.
     *         - tags[] string a single tag - must not start with an underscore
     *     - subaccount string the unique id of a subaccount for this message - must already exist or will fail with an error
     *     - google_analytics_domains array an array of strings indicating for which any matching URLs will automatically have Google Analytics parameters appended to their query string automatically.
     *     - google_analytics_campaign array|string optional string indicating the value to set for the utm_campaign tracking parameter. If this isn't provided the email's from address will be used instead.
     *     - metadata array metadata an associative array of user metadata. Mandrill will store this metadata and make it available for retrieval. In addition, you can select up to 10 metadata fields to index and make searchable using the Mandrill search api.
     *     - recipient_metadata array Per-recipient metadata that will override the global values specified in the metadata parameter.
     *         - recipient_metadata[] struct metadata for a single recipient
     *             - rcpt string the email address of the recipient that the metadata is associated with
     *             - values array an associated array containing the recipient's unique metadata. If a key exists in both the per-recipient metadata and the global metadata, the per-recipient metadata will be used.
     *     - attachments array an array of supported attachments to add to the message
     *         - attachments[] struct a single supported attachment
     *             - type string the MIME type of the attachment
     *             - name string the file name of the attachment
     *             - content string the content of the attachment as a base64-encoded string
     *     - images array an array of embedded images to add to the message
     *         - images[] struct a single embedded image
     *             - type string the MIME type of the image - must start with "image/"
     *             - name string the Content ID of the image - use <img src="cid:THIS_VALUE"> to reference the image in your HTML content
     *             - content string the content of the image as a base64-encoded string
     * @param boolean $async enable a background sending mode that is optimized for bulk sending. In async mode, messages/send will immediately return a status of "queued" for every recipient. To handle rejections when sending in async mode, set up a webhook for the 'reject' event. Defaults to false for messages with no more than 10 recipients; messages with more than 10 recipients are always sent asynchronously, regardless of the value of async.
     * @param string $ip_pool the name of the dedicated ip pool that should be used to send the message. If you do not have any dedicated IPs, this parameter has no effect. If you specify a pool that does not exist, your default pool will be used instead.
     * @param string $send_at when this message should be sent as a UTC timestamp in YYYY-MM-DD HH:MM:SS format. If you specify a time in the past, the message will be sent immediately. An additional fee applies for scheduled email, and this feature is only available to accounts with a positive balance.
     * @return array of structs for each recipient containing the key "email" with the email address, and details of the message status for that recipient
     *     - return[] struct the sending results for a single recipient
     *         - email string the email address of the recipient
     *         - status string the sending status of the recipient - either "sent", "queued", "rejected", or "invalid"
     *         - reject_reason string the reason for the rejection if the recipient status is "rejected" - one of "hard-bounce", "soft-bounce", "spam", "unsub", "custom", "invalid-sender", "invalid", "test-mode-limit", or "rule"
     *         - _id string the message's unique id
     */
    public function sendTemplate($template_name, $template_content, $message, $async=false, $ip_pool=null, $send_at=null) {
        $_params = array("template_name" => $template_name, "template_content" => $template_content, "message" => $message, "async" => $async, "ip_pool" => $ip_pool, "send_at" => $send_at);
        return $this->master->call('messages/send-template', $_params);
    }

    /**
     * Search recently sent messages and optionally narrow by date range, tags, senders, and API keys. If no date range is specified, results within the last 7 days are returned. This method may be called up to 20 times per minute. If you need the data more often, you can use <a href="/api/docs/messages.html#method=info">/messages/info.json</a> to get the information for a single message, or <a href="http://help.mandrill.com/entries/21738186-Introduction-to-Webhooks">webhooks</a> to push activity to your own application for querying.
     * @param string $query <a href="http://help.mandrill.com/entries/22211902">search terms</a> to find matching messages
     * @param string $date_from start date
     * @param string $date_to end date
     * @param array $tags an array of tag names to narrow the search to, will return messages that contain ANY of the tags
     * @param array $senders an array of sender addresses to narrow the search to, will return messages sent by ANY of the senders
     * @param array $api_keys an array of API keys to narrow the search to, will return messages sent by ANY of the keys
     * @param integer $limit the maximum number of results to return, defaults to 100, 1000 is the maximum
     * @return array of structs for each matching message
     *     - return[] struct the information for a single matching message
     *         - ts integer the Unix timestamp from when this message was sent
     *         - _id string the message's unique id
     *         - sender string the email address of the sender
     *         - template string the unique name of the template used, if any
     *         - subject string the message's subject line
     *         - email string the recipient email address
     *         - tags array list of tags on this message
     *             - tags[] string individual tag on this message
     *         - opens integer how many times has this message been opened
     *         - opens_detail array list of individual opens for the message
     *             - opens_detail[] struct information on an individual open
     *                 - ts integer the unix timestamp from when the message was opened
     *                 - ip string the IP address that generated the open
     *                 - location string the approximate region and country that the opening IP is located
     *                 - ua string the email client or browser data of the open
     *         - clicks integer how many times has a link been clicked in this message
     *         - clicks_detail array list of individual clicks for the message
     *             - clicks_detail[] struct information on an individual click
     *                 - ts integer the unix timestamp from when the message was clicked
     *                 - url string the URL that was clicked on
     *                 - ip string the IP address that generated the click
     *                 - location string the approximate region and country that the clicking IP is located
     *                 - ua string the email client or browser data of the click
     *         - state string sending status of this message: sent, bounced, rejected
     *         - metadata struct any custom metadata provided when the message was sent
     *     - smtp_events array a log of up to 3 smtp events for the message
     *         - smtp_events[] struct information about a specific smtp event
     *             - ts integer the Unix timestamp when the event occured
     *             - type string the message's state as a result of this event
     *             - diag string the SMTP response from the recipient's server
     */
    public function search($query='*', $date_from=null, $date_to=null, $tags=null, $senders=null, $api_keys=null, $limit=100) {
        $_params = array("query" => $query, "date_from" => $date_from, "date_to" => $date_to, "tags" => $tags, "senders" => $senders, "api_keys" => $api_keys, "limit" => $limit);
        return $this->master->call('messages/search', $_params);
    }

    /**
     * Search the content of recently sent messages and return the aggregated hourly stats for matching messages
     * @param string $query the search terms to find matching messages for
     * @param string $date_from start date
     * @param string $date_to end date
     * @param array $tags an array of tag names to narrow the search to, will return messages that contain ANY of the tags
     * @param array $senders an array of sender addresses to narrow the search to, will return messages sent by ANY of the senders
     * @return array the array of history information
     *     - return[] struct the stats for a single hour
     *         - time string the hour as a UTC date string in YYYY-MM-DD HH:MM:SS format
     *         - sent integer the number of emails that were sent during the hour
     *         - hard_bounces integer the number of emails that hard bounced during the hour
     *         - soft_bounces integer the number of emails that soft bounced during the hour
     *         - rejects integer the number of emails that were rejected during the hour
     *         - complaints integer the number of spam complaints received during the hour
     *         - unsubs integer the number of unsubscribes received during the hour
     *         - opens integer the number of emails opened during the hour
     *         - unique_opens integer the number of unique opens generated by messages sent during the hour
     *         - clicks integer the number of tracked URLs clicked during the hour
     *         - unique_clicks integer the number of unique clicks generated by messages sent during the hour
     */
    public function searchTimeSeries($query='*', $date_from=null, $date_to=null, $tags=null, $senders=null) {
        $_params = array("query" => $query, "date_from" => $date_from, "date_to" => $date_to, "tags" => $tags, "senders" => $senders);
        return $this->master->call('messages/search-time-series', $_params);
    }

    /**
     * Get the information for a single recently sent message
     * @param string $id the unique id of the message to get - passed as the "_id" field in webhooks, send calls, or search calls
     * @return struct the information for the message
     *     - ts integer the Unix timestamp from when this message was sent
     *     - _id string the message's unique id
     *     - sender string the email address of the sender
     *     - template string the unique name of the template used, if any
     *     - subject string the message's subject line
     *     - email string the recipient email address
     *     - tags array list of tags on this message
     *         - tags[] string individual tag on this message
     *     - opens integer how many times has this message been opened
     *     - opens_detail array list of individual opens for the message
     *         - opens_detail[] struct information on an individual open
     *             - ts integer the unix timestamp from when the message was opened
     *             - ip string the IP address that generated the open
     *             - location string the approximate region and country that the opening IP is located
     *             - ua string the email client or browser data of the open
     *     - clicks integer how many times has a link been clicked in this message
     *     - clicks_detail array list of individual clicks for the message
     *         - clicks_detail[] struct information on an individual click
     *             - ts integer the unix timestamp from when the message was clicked
     *             - url string the URL that was clicked on
     *             - ip string the IP address that generated the click
     *             - location string the approximate region and country that the clicking IP is located
     *             - ua string the email client or browser data of the click
     *     - state string sending status of this message: sent, bounced, rejected
     *     - metadata struct any custom metadata provided when the message was sent
     *     - smtp_events array a log of up to 3 smtp events for the message
     *         - smtp_events[] struct information about a specific smtp event
     *             - ts integer the Unix timestamp when the event occured
     *             - type string the message's state as a result of this event
     *             - diag string the SMTP response from the recipient's server
     */
    public function info($id) {
        $_params = array("id" => $id);
        return $this->master->call('messages/info', $_params);
    }

    /**
     * Get the full content of a recently sent message
     * @param string $id the unique id of the message to get - passed as the "_id" field in webhooks, send calls, or search calls
     * @return struct the content of the message
     *     - ts integer the Unix timestamp from when this message was sent
     *     - _id string the message's unique id
     *     - from_email string the email address of the sender
     *     - from_name string the alias of the sender (if any)
     *     - subject string the message's subject line
     *     - to struct the message recipient's information
     *         - email string the email address of the recipient
     *         - name string the alias of the recipient (if any)
     *     - tags array list of tags on this message
     *         - tags[] string individual tag on this message
     *     - headers struct the key-value pairs of the custom MIME headers for the message's main document
     *     - text string the text part of the message, if any
     *     - html string the HTML part of the message, if any
     *     - attachments array an array of any attachments that can be found in the message
     *         - attachments[] struct information about an individual attachment
     *             - name string the file name of the attachment
     *             - type string the MIME type of the attachment
     *             - content string the content of the attachment as a base64 encoded string
     */
    public function content($id) {
        $_params = array("id" => $id);
        return $this->master->call('messages/content', $_params);
    }

    /**
     * Parse the full MIME document for an email message, returning the content of the message broken into its constituent pieces
     * @param string $raw_message the full MIME document of an email message
     * @return struct the parsed message
     *     - subject string the subject of the message
     *     - from_email string the email address of the sender
     *     - from_name string the alias of the sender (if any)
     *     - to array an array of any recipients in the message
     *         - to[] struct the information on a single recipient
     *             - email string the email address of the recipient
     *             - name string the alias of the recipient (if any)
     *     - headers struct the key-value pairs of the MIME headers for the message's main document
     *     - text string the text part of the message, if any
     *     - html string the HTML part of the message, if any
     *     - attachments array an array of any attachments that can be found in the message
     *         - attachments[] struct information about an individual attachment
     *             - name string the file name of the attachment
     *             - type string the MIME type of the attachment
     *             - binary boolean if this is set to true, the attachment is not pure-text, and the content will be base64 encoded
     *             - content string the content of the attachment as a text string or a base64 encoded string based on the attachment type
     *     - images array an array of any embedded images that can be found in the message
     *         - images[] struct information about an individual image
     *             - name string the Content-ID of the embedded image
     *             - type string the MIME type of the image
     *             - content string the content of the image as a base64 encoded string
     */
    public function parse($raw_message) {
        $_params = array("raw_message" => $raw_message);
        return $this->master->call('messages/parse', $_params);
    }

    /**
     * Take a raw MIME document for a message, and send it exactly as if it were sent through Mandrill's SMTP servers
     * @param string $raw_message the full MIME document of an email message
     * @param string|null $from_email optionally define the sender address - otherwise we'll use the address found in the provided headers
     * @param string|null $from_name optionally define the sender alias
     * @param array|null $to optionally define the recipients to receive the message - otherwise we'll use the To, Cc, and Bcc headers provided in the document
     *     - to[] string the email address of the recipient
     * @param boolean $async enable a background sending mode that is optimized for bulk sending. In async mode, messages/sendRaw will immediately return a status of "queued" for every recipient. To handle rejections when sending in async mode, set up a webhook for the 'reject' event. Defaults to false for messages with no more than 10 recipients; messages with more than 10 recipients are always sent asynchronously, regardless of the value of async.
     * @param string $ip_pool the name of the dedicated ip pool that should be used to send the message. If you do not have any dedicated IPs, this parameter has no effect. If you specify a pool that does not exist, your default pool will be used instead.
     * @param string $send_at when this message should be sent as a UTC timestamp in YYYY-MM-DD HH:MM:SS format. If you specify a time in the past, the message will be sent immediately.
     * @param string $return_path_domain a custom domain to use for the messages's return-path
     * @return array of structs for each recipient containing the key "email" with the email address, and details of the message status for that recipient
     *     - return[] struct the sending results for a single recipient
     *         - email string the email address of the recipient
     *         - status string the sending status of the recipient - either "sent", "queued", "scheduled", "rejected", or "invalid"
     *         - reject_reason string the reason for the rejection if the recipient status is "rejected" - one of "hard-bounce", "soft-bounce", "spam", "unsub", "custom", "invalid-sender", "invalid", "test-mode-limit", or "rule"
     *         - _id string the message's unique id
     */
    public function sendRaw($raw_message, $from_email=null, $from_name=null, $to=null, $async=false, $ip_pool=null, $send_at=null, $return_path_domain=null) {
        $_params = array("raw_message" => $raw_message, "from_email" => $from_email, "from_name" => $from_name, "to" => $to, "async" => $async, "ip_pool" => $ip_pool, "send_at" => $send_at, "return_path_domain" => $return_path_domain);
        return $this->master->call('messages/send-raw', $_params);
    }

    /**
     * Queries your scheduled emails by sender or recipient, or both.
     * @param string $to an optional recipient address to restrict results to
     * @return array a list of up to 1000 scheduled emails
     *     - return[] struct a scheduled email
     *         - _id string the scheduled message id
     *         - created_at string the UTC timestamp when the message was created, in YYYY-MM-DD HH:MM:SS format
     *         - send_at string the UTC timestamp when the message will be sent, in YYYY-MM-DD HH:MM:SS format
     *         - from_email string the email's sender address
     *         - to string the email's recipient
     *         - subject string the email's subject
     */
    public function listScheduled($to=null) {
        $_params = array("to" => $to);
        return $this->master->call('messages/list-scheduled', $_params);
    }

    /**
     * Cancels a scheduled email.
     * @param string $id a scheduled email id, as returned by any of the messages/send calls or messages/list-scheduled
     * @return struct information about the scheduled email that was cancelled.
     *     - _id string the scheduled message id
     *     - created_at string the UTC timestamp when the message was created, in YYYY-MM-DD HH:MM:SS format
     *     - send_at string the UTC timestamp when the message will be sent, in YYYY-MM-DD HH:MM:SS format
     *     - from_email string the email's sender address
     *     - to string the email's recipient
     *     - subject string the email's subject
     */
    public function cancelScheduled($id) {
        $_params = array("id" => $id);
        return $this->master->call('messages/cancel-scheduled', $_params);
    }

    /**
     * Reschedules a scheduled email.
     * @param string $id a scheduled email id, as returned by any of the messages/send calls or messages/list-scheduled
     * @param string $send_at the new UTC timestamp when the message should sent. Mandrill can't time travel, so if you specify a time in past the message will be sent immediately
     * @return struct information about the scheduled email that was rescheduled.
     *     - _id string the scheduled message id
     *     - created_at string the UTC timestamp when the message was created, in YYYY-MM-DD HH:MM:SS format
     *     - send_at string the UTC timestamp when the message will be sent, in YYYY-MM-DD HH:MM:SS format
     *     - from_email string the email's sender address
     *     - to string the email's recipient
     *     - subject string the email's subject
     */
    public function reschedule($id, $send_at) {
        $_params = array("id" => $id, "send_at" => $send_at);
        return $this->master->call('messages/reschedule', $_params);
    }

}


