<?php
/*
 * mailTemplate is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version.
 *
 * mailTemplate is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * mailTemplate. If not, see <https://www.gnu.org/licenses/>.
 */

/**
 * Send an email using a PHP template file.
 *
 * This function causes the PHP engine to parse the PHP file specified by #_filename, with the variables passed in the
 * variable #_v, which should output an [RFC-822](https://tools.ietf.org/html/rfc822) (and its
 * [successors](https://en.wikipedia.org/wiki/Email#Message_format)) style message.
 * The function then extracts the headers from the message, grabs the "To" and "Subject" lines from it, and then passes
 * the "To:", "Subject:", message body, and remaining headers, to the PHP
 * [mail()](https://secure.php.net/manual/en/function.mail.php) function.
 *
 * As an example, consider template file "thanks.php"
 *
 *	To: <<?= $email ?>>
 *	Subject: Thank you for your request
 *	Content-Type: text/plain; charset=utf-8
 *
 *	Dear <?= $name =>,
 *
 *	Thankyou for your request, one of our staff will contact you <?= $when =>.
 *	<?php if ($important) { ?>
 *
 *	Your request is important to us.
 *	<?php } ?>
 *    
 * Which could then be called with:
 *
 *	mailTemplate("thanks.php", [
 *		'email' => "dave@example.com",
 *		'name' => "Dave",
 *		'when' => "tomorrow",
 *		'important' => FALSE,
 *	]};
 *
 * Note that, as of this implementation, #_filename is read using
 * [include](https://secure.php.net/manual/en/function.include.php), so it uses the file-finding rules defined therein.
 * 
 * Also, it is worth remembering that PHP eats newlines directly following a PHP close tag. Therefore, if you have:
 *
 *	To: <?= $recipient ?>
 *	Subject: ...
 *
 * Then the newline following the close tag will be eaten by the PHP parser, and you'll end up with:
 *
 *	To: example@example.comSubject: ...
 *
 * To work around this, you need to either make the closing tag not the last thing on the line (e.g. by adding a
 * trailing space to the line), or forcibly output a newline yourself from within the PHP, e.g.:
 *
 *	To: <?= $recipient."\n" ?>
 *	Subject: ...
 *
 * @param string $_filename Filename of PHP template file to send.
 * @param mixed $_v Associated array of variables to be made available to the mail template.
 *
 * @return bool TRUE on success, FALSE on failure.
 */
function mailTemplate($_filename, $_v)
{
	ob_start();
	extract($_v, EXTR_OVERWRITE);
	if (!include($_filename)) {
		/* Don't need to raise a warning here, include will do that for us. */
		ob_end_clean();
		return FALSE;
	}
	$email = explode("\n", ob_get_clean());

	$to = "";
	$subject = "";
	$headers = [];
	for ($i = 0; $i < count($email); ++$i) {
		$line = rtrim($email[$i], "\r");
		if ($line == "") {
			++$i;
			break;
		}
		$matches = [];
		if (preg_match("/^([^:]+): (.*)/", $line, $matches) != 1) {
			error_log("mailTemplate: " . $_filename . ":" . $i . ": Invalid header: ". $line);
			return FALSE;
		}
		if ($matches[1] == "To") {
			$to = $matches[2];
		}
		else if ($matches[1] == "Subject") {
			$subject = $matches[2];
		}
		else {
			$headers[] = $line;
		}
	}

	$missing = [];
	if ($to == "")
		$missing[] = "To:";
	if ($subject == "")
		$missing[] = "Subject:";
	if (count($missing)) {
		error_log("mailTemplate: " . $_filename . ":" . $i . ": Missing header(s): " . implode(", ", $missing));
		return FALSE;
	}
	if ($i >= count($email)) {
		error_log("mailTemplate: " . $_filename . ":" . $i . ": Missing email body");
		return FALSE;
	}

	if (isset($GLOBALS['_DEBUG']) && $GLOBALS['_DEBUG']) {
		echo "To: {$to}\r\n";
		echo "Subject: {$subject}\r\n";
		if (count($headers)) {
			echo implode("\r\n", $headers)."\r\n";
		}
		echo "\r\n";
		echo implode("\n", array_slice($email, $i));
		return TRUE;
	}

	return mail($to, $subject, implode("\n", array_slice($email, $i)), implode("\r\n", $headers));
}

?>