trolley/reciver.php

<?php
        function read_and_delete_first_line($filename) // This function will delete the first line of db.txt.
        {
                $file = file($filename); //Makes the contents of db.txt into an array.
                array_shift($file); //Removes the first element of the array.
                file_put_contents($filename, $file); //Rewrites db.txt with the contents of the array.
        }
        $decoded_location  = json_decode(file_get_contents('php://input')); //Receives input from app and decodes the json recived.
        $decoded_location->inTime = gmdate('H:i:s',time()); //Adds a new property to the object we get after decoding the json and stores the current time.
	$encoded_location = json_encode($decoded_location); //Reencodes the object back into a json with the new inTime property.
        $file = 'db.txt';
        $totalLines = intval(exec("wc -l '$file'")); //Counts how many lines db.txt has.
        //echo $totalLines. "\n"; //For testing purposes
        if($totalLines > 15) //If db.txt has more than a specified amount of lines, it will delete the first line of db.txt.
        {
                read_and_delete_first_line("db.txt");
        }

        $db = fopen("db.txt","a") or die("FAILED TO ACCESS DATABASE"); //Opens db.txt in append mode. If it somehow fails to open the database, an error message will be displayed.
        fwrite($db,$encoded_location. "\n"); //Writes the newly encoded json into db.txt.
        fclose($db); //Closes db.txt
        //$totalLines = intval(exec("wc -l '$file'")); //For testing purposes
        //echo $totalLines; //For testing purposes
?>