class Constraint

class Constraint {
    
    /**
     * The constraint represented as a string. For example '>=8.x-5.x'.
     *
     * @var string
     */
    protected $constraint;
    
    /**
     * A list of associative arrays representing the constraint.
     *
     * Each containing the keys:
     *  - 'op': can be one of: '=', '==', '!=', '<>', '<', '<=', '>', or '>='.
     *  - 'version': A complete version, e.g. '4.5-beta3'.
     *
     * @var array[]
     */
    protected $constraintArray = [];
    
    /**
     * Constraint constructor.
     *
     * @param string $constraint
     *   The constraint string to create the object from. For example, '>8.x-1.1'.
     * @param string $core_compatibility
     *   Core compatibility declared for the current version of Drupal core.
     *   Normally this is set to \Drupal::CORE_COMPATIBILITY by the caller.
     */
    public function __construct($constraint, $core_compatibility) {
        $this->constraint = $constraint;
        $this->parseConstraint($constraint, $core_compatibility);
    }
    
    /**
     * Gets the constraint as a string.
     *
     * Can be used in the UI for reporting incompatibilities.
     *
     * @return string
     *   The constraint as a string.
     */
    public function __toString() {
        return $this->constraint;
    }
    
    /**
     * Determines if the provided version is satisfied by this constraint.
     *
     * @param string $version
     *   The version to check, for example '4.2'.
     *
     * @return bool
     *   TRUE if the provided version is satisfied by this constraint, FALSE if
     *   not.
     */
    public function isCompatible($version) {
        foreach ($this->constraintArray as $constraint) {
            if (!version_compare($version, $constraint['version'], $constraint['op'])) {
                return FALSE;
            }
        }
        return TRUE;
    }
    
    /**
     * Parses a constraint string.
     *
     * @param string $constraint_string
     *   The constraint string to parse.
     * @param string $core_compatibility
     *   Core compatibility declared for the current version of Drupal core.
     *   Normally this is set to \Drupal::CORE_COMPATIBILITY by the caller.
     */
    private function parseConstraint($constraint_string, $core_compatibility) {
        // We use named sub-patterns and support every op that version_compare
        // supports. Also, op is optional and defaults to equals.
        $p_op = '(?<operation>!=|==|=|<|<=|>|>=|<>)?';
        // Core version is always optional: 8.x-2.x and 2.x is treated the same.
        $p_core = '(?:' . preg_quote($core_compatibility) . '-)?';
        $p_major = '(?<major>\\d+)';
        // By setting the minor version to x, branches can be matched.
        $p_minor = '(?<minor>(?:\\d+|x)(?:-[A-Za-z]+\\d+)?)';
        foreach (explode(',', $constraint_string) as $constraint) {
            if (preg_match("/^\\s*{$p_op}\\s*{$p_core}{$p_major}\\.{$p_minor}/", $constraint, $matches)) {
                $op = !empty($matches['operation']) ? $matches['operation'] : '=';
                if ($matches['minor'] == 'x') {
                    // Drupal considers "2.x" to mean any version that begins with
                    // "2" (e.g. 2.0, 2.9 are all "2.x"). PHP's version_compare(),
                    // on the other hand, treats "x" as a string; so to
                    // version_compare(), "2.x" is considered less than 2.0. This
                    // means that >=2.x and <2.x are handled by version_compare()
                    // as we need, but > and <= are not.
                    if ($op == '>' || $op == '<=') {
                        $matches['major']++;
                    }
                    // Equivalence can be checked by adding two restrictions.
                    if ($op == '=' || $op == '==') {
                        $this->constraintArray[] = [
                            'op' => '<',
                            'version' => $matches['major'] + 1 . '.x',
                        ];
                        $op = '>=';
                    }
                }
                $this->constraintArray[] = [
                    'op' => $op,
                    'version' => $matches['major'] . '.' . $matches['minor'],
                ];
            }
        }
    }

}