class BinaryOperator

abstract class BinaryOperator extends Operator {
    
    /**
     * @psalm-var list<Constraint>
     */
    private readonly array $constraints;
    protected function __construct(mixed ...$constraints) {
        $this->constraints = array_map(fn($constraint): Constraint => $this->checkConstraint($constraint), $constraints);
    }
    
    /**
     * Returns the number of operands (constraints).
     */
    public final function arity() : int {
        return count($this->constraints);
    }
    
    /**
     * Returns a string representation of the constraint.
     */
    public function toString() : string {
        $reduced = $this->reduce();
        if ($reduced !== $this) {
            return $reduced->toString();
        }
        $text = '';
        foreach ($this->constraints as $key => $constraint) {
            $constraint = $constraint->reduce();
            $text .= $this->constraintToString($constraint, $key);
        }
        return $text;
    }
    
    /**
     * Counts the number of constraint elements.
     */
    public function count() : int {
        $count = 0;
        foreach ($this->constraints as $constraint) {
            $count += count($constraint);
        }
        return $count;
    }
    
    /**
     * @psalm-return list<Constraint>
     */
    protected final function constraints() : array {
        return $this->constraints;
    }
    
    /**
     * Returns true if the $constraint needs to be wrapped with braces.
     */
    protected final function constraintNeedsParentheses(Constraint $constraint) : bool {
        return $this->arity() > 1 && parent::constraintNeedsParentheses($constraint);
    }
    
    /**
     * Reduces the sub-expression starting at $this by skipping degenerate
     * sub-expression and returns first descendant constraint that starts
     * a non-reducible sub-expression.
     *
     * See Constraint::reduce() for more.
     */
    protected function reduce() : Constraint {
        if ($this->arity() === 1 && $this->constraints[0] instanceof Operator) {
            return $this->constraints[0]
                ->reduce();
        }
        return parent::reduce();
    }
    
    /**
     * Returns string representation of given operand in context of this operator.
     */
    private function constraintToString(Constraint $constraint, int $position) : string {
        $prefix = '';
        if ($position > 0) {
            $prefix = ' ' . $this->operator() . ' ';
        }
        if ($this->constraintNeedsParentheses($constraint)) {
            return $prefix . '( ' . $constraint->toString() . ' )';
        }
        $string = $constraint->toStringInContext($this, $position);
        if ($string === '') {
            $string = $constraint->toString();
        }
        return $prefix . $string;
    }

}