<?php declare(strict_types=1);

namespace tests\unit;

use BadMethodCallException;

class Immutable
{
    private $a;
    private $b;
    private $c;

    protected $set = false;

    /**
     * Returns an instance clone that is now immutable, further calls to with<Name> wiill return clones
     * @throws BadMethodCallException if already set
     */
    public function set(): Immutable
    {
        if ($this->set) {
            throw new BadMethodCallException("Instance is already set!");
        }
        $new = clone $this;
        $new->set = true;
        return $new;
    }

    public function isHard(): bool { return $this->set; }

    private function with(string $name, $value): Immutable
    {
        $new = $this->set ? clone $this : $this;
        $new->{$name} = $value;
        return $new;
    }

    public function withA(string $value): Immutable { return $this->with('a', $value); }
    public function withB(string $value): Immutable { return $this->with('b', $value); }
    public function withC(string $value): Immutable { return $this->with('c', $value); }
    public function __toString() { return "{$this->a} : {$this->b} : {$this->c}"; }
}

class ImmutableTest extends \PHPUnit\Framework\TestCase
{
    public function testThatDemonstrateUseCase()
    {
        // Semi builder pattern, but without needless instance generation
        $blank = (new Immutable)
            ->withA('Alpacca') // update $blank
            ->withC('Whool') // update $blank
            ->set() // $blank is from now on immutable
        ;

        $one = $blank->withB('Cool');
        $two = $blank->withB('Warm');

        $this->assertTrue($blank->isHard());
        $this->assertTrue($one->isHard());
        $this->assertTrue($two->isHard());

        $this->assertNotSame($blank, $one);
        $this->assertNotSame($blank, $two);
        $this->assertNotSame($one, $two);

        $this->assertEquals("Alpacca :  : Whool", $blank);
        $this->assertEquals("Alpacca : Cool : Whool", $one);
        $this->assertEquals("Alpacca : Warm : Whool", $two);
    }

    public function testUndefined()
    {
        $this->expectException(BadMethodCallException::class);
        $this->expectExceptionMessage("Instance is already set");
        $c = (new Immutable)->set()->withA('a')->set();
    }
}