process-changelog.php

<?php

$source_file = 'readme.txt';

$target_file_pro  = 'tmp/changelog-pro.md';
$target_file_free = 'tmp/changelog-free.md';

$handle = fopen($source_file, 'r');

$changelog_pro  = [];
$changelog_free = [];

if ($handle) {
    $write_mode = null;

    while (($line = fgets($handle)) !== false) {

      if (strpos($line, 'Changelog') == true) {
          array_push($changelog_pro, $line);
          array_push($changelog_free, $line);
          continue;
      }

      // set up write mode
      if (strpos($line, 'fs_premium_only_begin')) {
        $write_mode = 'pro';
        continue;
      } else if(strpos($line, 'fs_free_only_begin')) {
        $write_mode = 'free';
        continue;
      }

      // never write if we're on an end directive
      if (strpos($line, 'fs_premium_only_end') || strpos($line, 'fs_free_only_end')) {
        continue;
      }

      if(!empty($write_mode) && $write_mode === 'pro') {
        array_push($changelog_pro, $line);
      } else if(!empty($write_mode) && $write_mode === 'free') {
        array_push($changelog_free, $line);
      }
    }

    fclose($handle);
} else {
    echo('error opening the file');
}

file_put_contents($target_file_pro, $changelog_pro);
file_put_contents($target_file_free, $changelog_free);