Gazelle/sections/ajax/send_recommendation.php

<?php
$FriendID = (int) $_POST['friend'];
$Type = $_POST['type'];
$ID = (int) $_POST['id'];
$Note = $_POST['note'];

if (empty($FriendID) || empty($Type) || empty($ID)) {
	echo json_encode(array("status" => "error", "response" => "Error."));
	die();
}
// Make sure the recipient is on your friends list and not some random dude.
$DB->query("
	SELECT
		f.FriendID,
		u.Username
	FROM friends AS f
		RIGHT JOIN users_enable_recommendations AS r
			ON r.ID = f.FriendID AND r.Enable = 1
		RIGHT JOIN users_main AS u
			ON u.ID = f.FriendID
	WHERE f.UserID = '$LoggedUser[ID]'
		AND f.FriendID = '$FriendID'");

if ($DB->record_count() == 0) {
	echo json_encode(array("status" => "error", "response" => "Not on friend list."));
	die();
}

$Type = strtolower($Type);
$Link = '';
// "a" vs "an", english language is so confusing.
// https://en.wikipedia.org/wiki/English_articles#Distinction_between_a_and_an
$Article = 'a';
switch ($Type) {
	case 'torrent':
		$Link = "torrents.php?id=".$ID;
		$DB->query("SELECT Name FROM torrents_group WHERE ID = '$ID'");
		break;
	case 'artist':
		$Article = "an";
		$Link = "artist.php?id=".$ID;
		$DB->query("SELECT Name FROM artists_group WHERE ArtistID = '$ID'");
		break;
	case 'collage':
		$Link = "collages.php?id=".$ID;
		$DB->query("SELECT Name FROM collages WHERE ID = '$ID'");
		break;
}
list($Name) = $DB->next_record();
$Subject = $LoggedUser['Username'] . " recommended you $Article " . $Type . "!";
$Body = $LoggedUser['Username'] . " recommended you the ".$Type." [url=https://".SSL_SITE_URL."/$Link]$Name".'[/url].';
if (!empty($Note)) {
	$Body = $Body . "\n\n". $Note;
}

Misc::send_pm($FriendID, $LoggedUser['ID'], $Subject, $Body);
echo json_encode(array("status" => "success", "response" => "Sent!"));
die();