example-bot.php

<?php
header("Content-type: application/json; charset=utf-8");
$username = !empty($_POST["username"]) ? strtolower($_POST["username"]) : false;
$message = !empty($_POST["message"]) ? $_POST["message"] : false;
$messageExploded = explode(" ", $message);
if ($messageExploded[0] === "text") {
	$outputArray[] = [
		"type" => "text",
		"message" => "Your username is " . $username
	];
	$outputArray[] = [
		"type" => "text",
		"message" => "Your username is " . $username
	];
} else if ($messageExploded[0] === "image") {
	$outputArray[] = [
		"type" => "image",
		"message" => "https://media3.giphy.com/media/3o7aDalHF4hE9Et8AM/giphy.gif"
	];
	$outputArray[] = [
		"type" => "text",
		"message" => "Happy Wednesday!"
	];
	$outputArray[] = [
		"type" => "image",
		"message" => "https://media3.giphy.com/media/3o7aDalHF4hE9Et8AM/giphy.gif"
	];
// bots must respond to blank @mentions.. either show an error asking for required parameter or auto fill with default ones
} else {
	$outputArray = [
		"type" => "text",
		"message" => "Send a parameter"
	];
}
echo json_encode($outputArray);
?>

instructions.md

Bot Instructions

Once you're done setting up your script go to any group and message @bot with a direct link to your webhook script. (Example: @bot https://your.domain/webhook.php)

Warning: Bot accounts can't respond through the site they can only message through webhooks. It's advised not to use a personal account.

Send @bot /remove to make your account not a bot again :)