Challenge 3 — Solution

Task: Create two custom exceptions, FileNotFoundException and
PermissionDeniedException, both extending Exception. Write a function
openFile($filename, $hasPermission) that throws the first if $filename
is an empty string, the second if $hasPermission is false, otherwise
echoes "File opened successfully." Use a try block with TWO separate
catch blocks (correctly ordered) to handle each case distinctly, with a
generic Exception catch as a final fallback.

<?php
    class FileNotFoundException extends Exception {}
    class PermissionDeniedException extends Exception {}

    function openFile(string $filename, bool $hasPermission) {
        if ($filename === '') {
            throw new FileNotFoundException("No filename was provided.");
        }
        if (!$hasPermission) {
            throw new PermissionDeniedException("You do not have permission to open '$filename'.");
        }
        echo "File opened successfully.";
    }

    try {
        openFile("secrets.txt", false);
    } catch (FileNotFoundException $e) {
        echo "File not found: " . $e->getMessage();
    } catch (PermissionDeniedException $e) {
        echo "Permission denied: " . $e->getMessage();
    } catch (Exception $e) {
        echo "Unexpected error: " . $e->getMessage();
    }
?>


Output:
Permission denied: You do not have permission to open 'secrets.txt'.

Notes:
- Both custom exception classes extend Exception directly with empty
  bodies, giving each a distinct, catchable type without needing any
  additional code beyond the class declaration itself.
- The three catch blocks are ordered from most specific to least
  specific: FileNotFoundException first, PermissionDeniedException
  second, and the generic Exception last as a catch-all fallback -
  reversing this order would let the generic Exception catch block
  intercept both specific exception types before they ever reached
  their own dedicated blocks.
- Since "secrets.txt" is a non-empty filename but $hasPermission is
  false, openFile() throws PermissionDeniedException specifically -
  execution skips the first catch block (which only matches
  FileNotFoundException) and lands in the second one instead.