convert_codestyle.php

<?php

function print_usage_and_exit(string $msg = '') {
    global $argv;
    fprintf(STDERR, "%sUsage: %s pathname.php\nConverts fooBar to foo_bar in variable names\n", $msg ? $msg . "\n" : '', $argv[0]);
    exit(1);
}

function convert_codestyle() {
    error_reporting(E_ALL);
    global $argv;
    if (count($argv) !== 2) {
        print_usage_and_exit();
    }
    $path = $argv[1];
    if (!file_exists($path)) {
        print_usage_and_exit("File '$path' does not exist");
    }
    $contents = file_get_contents($path);
    // Conservatively replace fooBar, but not fooBAR or fooB
    $new_contents = preg_replace_callback('@(\$)([a-z][A-Za-z0-9]*([A-Z][a-z0-9]+)+)\b@', function(array $args) : string {
        list($prefix, $msg) = $args;
        return $args[1] . preg_replace_callback('@[A-Z][a-z0-9]@', function(array $inner_args) {

            $msg = $inner_args[0];
            assert(strlen($msg) === 2);
            return '_' . strtolower($msg[0]) . $msg[1];
        }, $args[2]);
    }, $contents);

    preg_match_all('@\bfunction\s+(_?[a-z]+(_[a-z]+)+)\s*\(@', $new_contents, $matches);
    $function_names = $matches[1];
    $function_names_set = array_flip($function_names);
    $new_contents = preg_replace_callback('@\b_?[a-z]+(_[a-z]+)+\b@', function(array $args) use ($function_names_set) : string {
        $name = $args[0];
        if (!isset($function_names_set[$name])) {
            return $name;
        }
        $name = ltrim($name, '_');
        $name = preg_replace_callback('@_[a-z]@', function(array $args) {
            $msg = $args[0];
            assert(strlen($msg) === 2);
            return strtoupper($msg[1]);
        }, $name);
        return $name;
    }, $new_contents);
    echo $new_contents;
}

convert_codestyle();