Challenge 3 — Solution

Task: Extend the worker loop from this chapter to dispatch to a
different function depending on the job's "type" column (using
match()), supporting both 'send_email' and 'resize_image' job types,
each with its own try/catch and markJobComplete/markJobFailed calls.
Explain in a comment what would happen if one job type's handler threw
an uncaught exception, with no try/catch around the dispatch at all.

<?php
    while (true) {
        $stmt = $pdo->query("SELECT * FROM jobs WHERE status = 'pending' LIMIT 1");
        $job = $stmt->fetch();

        if ($job) {
            $payload = json_decode($job['payload'], true);

            try {
                match ($job['type']) {
                    'send_email' => sendEmail($payload['to'], $payload['subject']),
                    'resize_image' => resizeImage($payload['source_path'], $payload['target_width'], $payload['target_height']),
                    default => throw new InvalidArgumentException("Unknown job type: {$job['type']}"),
                };
                markJobComplete($pdo, $job['id']);
            } catch (Exception $e) {
                markJobFailed($pdo, $job['id'], $e->getMessage());
            }
        } else {
            sleep(2);
        }
    }

    // What would happen with no try/catch around the dispatch at all:
    // If either sendEmail() or resizeImage() threw an exception (a
    // real, plausible outcome - a mail server timeout, a corrupted
    // image file) and there were no try/catch wrapping the match()
    // call, the exception would propagate all the way up and out of
    // the while(true) loop entirely, since nothing in this script
    // would catch it. This would crash the ENTIRE worker process, not
    // just fail the one problematic job - every other pending job in
    // the queue (including completely unrelated, perfectly healthy
    // ones) would then sit unprocessed indefinitely, since the worker
    // that was supposed to keep polling for them is no longer running
    // at all. This is exactly the reasoning behind the chapter's own
    // warn-box: a failed job must be handled deliberately (caught,
    // marked 'failed', and the loop allowed to continue) rather than
    // allowed to silently (or catastrophically) take down the whole
    // background-processing system.
?>


Notes:
- match($job['type']) dispatches to the correct handler based purely
  on the job's own stored type column, with a default arm throwing a
  clear InvalidArgumentException for any genuinely unrecognised type -
  reusing the exact match()-with-a-default-throw pattern from Chapter
  2's own NotificationFactory example.
- Both sendEmail() and resizeImage() are called inside the SAME
  try/catch block here, rather than each needing its own separate
  try/catch - since match() itself already selects exactly one branch
  to run, a single surrounding try/catch correctly covers whichever one
  actually executes for a given job.
- markJobComplete()/markJobFailed() are called exactly once per loop
  iteration, immediately after the try/catch resolves either way - this
  keeps the worker's own job-status bookkeeping consistent regardless
  of which job type or outcome occurred.