Case builder for Doctrine

CaseBuilder.php

<?php

declare(strict_types=1);

interface WhenClauseInterface
{
    public function then(string $result): CaseBuilder;
}

use Ds\Vector;
use function implode;
use InvalidArgumentException;

final class CaseBuilder
{
    /**
     * @var Vector<array{when: string, then: string}> $whenClauses
     */
    public readonly Vector $whenClauses;

    private ?string $elseClause;
    private ?string $caseExpression;

    private function __construct()
    {
        $this->whenClauses = new Vector();
        $this->elseClause = null;
        $this->caseExpression = null;
    }

    public static function new(): static
    {
        return new self();
    }

    public static function expression(string $expression): static
    {
        $new = new self();
        $new->caseExpression = $expression;
        return $new;
    }

    public function when(string $condition): WhenClauseInterface
    {
        return new class($this, $condition) implements WhenClauseInterface {
            public function __construct(
                private CaseBuilder $caseBuilder,
                private string $condition
            ) {}

            public function then(string $result): CaseBuilder
            {
                $new = clone $this->caseBuilder;
                $new->whenClauses = $this->caseBuilder->whenClauses->copy();
                $new->whenClauses->push(['when' => $this->condition, 'then' => $result]);
                return $new;
            }
        };
    }

    public function else(string $result): static
    {
        $new = clone $this;
        $new->elseClause = $result;
        return $new;
    }

    public function build(): string
    {
        if ($this->whenClauses->isEmpty()) {
            throw new InvalidArgumentException(
                'CASE statement must have at least one WHEN clause'
            );
        }

        $parts = [];

        if ($this->caseExpression !== null) {
            $parts[] = "CASE {$this->caseExpression}";
        } else {
            $parts[] = 'CASE';
        }

        foreach ($this->whenClauses as $clause) {
            $parts[] = "WHEN {$clause['when']} THEN '{$clause['then']}'";
        }

        if ($this->elseClause !== null) {
            $parts[] = "ELSE '{$this->elseClause}'";
        }

        $parts[] = 'END';

        return implode(' ', $parts);
    }
}

// Usage:
$foo = CaseBuilder::new()
    ->when('permissao.id = 1')
    ->then('true')
    ->else('false')
    ->build();
// CASE WHEN permission.id = 1 THEN 'true' ELSE 'false' END

$bar = CaseBuilder::expression('permission.id')
        ->when('1')
        ->then('Foo')
        ->when('2')
        ->then('Bar')
        ->else('unknown')
        ->build();
// CASE permission.id WHEN 1 THEN 'Foo' WHEN 2 THEN 'Bar' ELSE 'unknown' END