<?php

/*
 * Dear Zane,
 *
 * In case you're interested, this is the program I used to create the 
 * encrypted messages for your Christmas mission this year.  I can
 * explain it to you if you like.  I just hope you had fun.
 *
 * Love,
 * Dad
 */

function gen_code(): array {
    $final_code = [];
    $code = [];
    for ($i = ord('a'); $i <= ord('z'); $i++) {
        $code[] = chr($i);
    }
    $values = $code;
    shuffle($values);
    for ($i = 0; $i < count($code); $i++) {
        $final_code[$code[$i]] = $values[$i];
    }

    return $final_code;
}

function shift_code(array $code, int $shift): array {
    $new_code = [];
    asort($code);
    $plain = array_keys($code);
    $cypher = array_values($code);
    for ($i = 0; $i < $shift; $i++) {
        $value = array_shift($plain);
        array_push($plain, $value);
    }

    return array_combine($plain, $cypher);
}

function encode(array $code, string $message): string {
    $result = '';
    $message = strtolower($message);
    for ($i = 0; $i < strlen($message); $i++) {
        if (isset($code[$message[$i]])) {
            $result .= $code[$message[$i]];
        }
    }

    return $result;
}

function decode(array $code, string $message): string {
    $result = '';
    $message = strtolower($message);
    $code = array_flip($code);
    for ($i = 0; $i < strlen($message); $i++) {
        if (isset($code[$message[$i]])) {
            $result .= $code[$message[$i]];
        }
    }

    return $result;
}

function print_code($code): void {
    asort($code);
    echo "Encoding is:\n";
    echo "CYPHER TEXT: ";
    foreach ($code as $k => $v) {
        echo strtoupper($v) . " ";
    }
    echo "\n";
    echo "PLAIN TEXT:  ";
    foreach ($code as $k => $v) {
        echo strtoupper($k) . " ";
    }
    echo "\n";
}

if (file_exists('xmas-code.txt')) {
    $code = require('xmas-code.txt');
} else {
    $code = gen_code();
    $output = "<?php\nreturn " . var_export($code, true) . ";\n";
    file_put_contents('xmas-code.txt', $output);
}

$command = $_SERVER['argv'][1] ?? '';
$message = $_SERVER['argv'][2] ?? '';
$shift = $_SERVER['argv'][3] ?? 0;

switch ($command) {
    case 'encode':
        echo encode($code, $message);
        break;
    case 'decode':
        echo decode($code, $message);
        break;
    case 'encode-shift':
        $code = shift_code($code, $shift);
        echo encode($code, $message);
        break;
    case 'decode-shift':
        $code = shift_code($code, $shift);
        echo decode($code, $message);
        break;
    case 'print-shift':
        $shift = $shift ?: (int)$message;
        $code = shift_code($code, $shift);
        print_code($code);
        break;
    case 'print':
    default:
        print_code($code);
        break;
}