The PHP API that powers my London Tube app for the Pebble Smartwatch. (http://matthewtole.com/pebble/#london-tube)

london-tube-status.php

<?php

// Include my shared functions.
include_once($_SERVER['DOCUMENT_ROOT'] . '/utils.php');

// The URL of the Tube Status API.
$API_URL = 'http://api.tubeupdates.com/?method=get.status&format=json';

// Mapping between shortcode and line name.
$line_codes = array(
  'BL' => 'bakerloo',
  'CE' => 'central',
  'CI' => 'circle',
  'DI' => 'district',
  'DL' => 'docklands',
  'HC' => 'hammersmithcity',
  'JL' => 'jubilee',
  'ME' => 'metropolitan',
  'NO' => 'northern',
  'OV' => 'overground',
  'PI' => 'piccadilly',
  'VI' => 'victoria',
  'WC' => 'waterloocity'
);

// Mapping between errors and numbers
$statuses = array(
  'good service' => 1,
  'part closure' => 2,
  'minor delays' => 4,
  'severe delays' => 8,
  'part suspended' => 16
);

// Grab the tube status and the incoming payload.
$tube_data = json_decode(file_get_contents($API_URL), true);
$payload = get_payload();

$order = $payload['0'];

// Start building the response.
$response = array(
  '0' => $order,
  '1' => ''
);

// Split the ordering string into the 2 character line short codes.
$lines = str_split($order, 2);
foreach ($lines as $pos => $line) {

  // Get the status for the line given its short code.
  $status = get_status_by_id($line_codes[$line]);

  // Do bitwise ORs on the status number to build it up
  $status_number = 0;
  foreach ($status as $st) {
    $status_number = $status_number |= $statuses[$st];
  }

  // Append the status code to the response string.
  $response['1'] .= str_pad($status_number, 2, ' ', STR_PAD_LEFT);
}

// Send the response.
send_response($response);

// Takes a line code (not shortcode) and returns an array of its current status.
function get_status_by_id($id) {
  global $tube_data;

  foreach ($tube_data['response']['lines'] as $index => $line) {
    if ($line['id'] == $id) {
      return explode(', ', $line['status']);
    }
  }
  return NULL;
}

?>

utils.php

function get_payload() {
  return json_decode(file_get_contents('php://input'), true);
}

function send_response($data) {
  $response = json_encode($data, JSON_FORCE_OBJECT);
  header('Content-Type: application/json');
  header('Content-Length: ' . strlen($response));
  echo $response;
  exit;
}