#!/usr/bin/env php
<?php

/*
 * sample-cli.php: a command-line PHP script that converts lengths.
 * Free sample from 99helpers.com/file-types/php
 * Run:  php sample-cli.php 5 km mi
 *       php sample-cli.php            (shows usage)
 * On macOS and Linux, chmod +x sample-cli.php then ./sample-cli.php 5 km mi
 *
 * 1. The shebang line: the PHP command-line interpreter skips it.
 * 2. This file is pure PHP, so it has no closing tag at the end. A stray
 *    newline after one would be printed as output.
 */

declare(strict_types=1);

// 3. Refuse to run inside a web server: this script reads $argv.
if (PHP_SAPI !== 'cli') {
    http_response_code(403);
    exit('Run this script from the command line.');
}

// 4. A backed enum (PHP 8.1+) with a method that uses match (PHP 8.0+).
enum Unit: string
{
    case Metre = 'm';
    case Kilometre = 'km';
    case Foot = 'ft';
    case Mile = 'mi';

    public function inMetres(): float
    {
        return match ($this) {
            Unit::Metre => 1.0,
            Unit::Kilometre => 1000.0,
            Unit::Foot => 0.3048,
            Unit::Mile => 1609.344,
        };
    }
}

function convert(float $value, Unit $from, Unit $to): float
{
    return $value * $from->inMetres() / $to->inMetres();
}

// 5. $argv holds the arguments; $argv[0] is the script name.
[$script, $value, $from, $to] = array_pad($argv, 4, null);
$units = implode(', ', array_map(fn (Unit $u) => $u->value, Unit::cases()));

if ($value === null || !is_numeric($value) || $from === null || $to === null) {
    // 6. Errors go to STDERR; the exit status tells the shell it failed.
    fwrite(STDERR, "Usage: php {$script} <number> <from> <to>   units: {$units}\n");
    fwrite(STDERR, "Example: php {$script} 5 km mi\n");
    exit(2);
}

// 7. tryFrom() returns null instead of throwing for an unknown unit.
$fromUnit = Unit::tryFrom($from);
$toUnit = Unit::tryFrom($to);
if ($fromUnit === null || $toUnit === null) {
    fwrite(STDERR, "Unknown unit. Use one of: {$units}\n");
    exit(2);
}

$result = convert((float) $value, $fromUnit, $toUnit);
printf("%s %s = %s %s\n", $value, $fromUnit->value, round($result, 4), $toUnit->value);