class JsonApiSpec

class JsonApiSpec {
    
    /**
     * The minimum supported specification version.
     *
     * @see http://jsonapi.org/format/#document-jsonapi-object
     */
    const SUPPORTED_SPECIFICATION_VERSION = '1.0';
    
    /**
     * The URI of the supported specification document.
     */
    const SUPPORTED_SPECIFICATION_PERMALINK = 'http://jsonapi.org/format/1.0/';
    
    /**
     * Member name: globally allowed characters.
     *
     * U+0080 and above (non-ASCII Unicode characters) are allowed, but are not
     * URL-safe. It is RECOMMENDED to not use them.
     *
     * A character class, for use in regular expressions.
     *
     * @see http://jsonapi.org/format/#document-member-names-allowed-characters
     * @see http://php.net/manual/en/regexp.reference.character-classes.php
     */
    const MEMBER_NAME_GLOBALLY_ALLOWED_CHARACTER_CLASS = '[a-zA-Z0-9\\x{80}-\\x{10FFFF}]';
    
    /**
     * Member name: allowed characters except as the first or last character.
     *
     * Space (U+0020) is allowed, but is not URL-safe. It is RECOMMENDED to not
     * use it.
     *
     * A character class, for use in regular expressions.
     *
     * @see http://jsonapi.org/format/#document-member-names-allowed-characters
     * @see http://php.net/manual/en/regexp.reference.character-classes.php
     */
    const MEMBER_NAME_INNER_ALLOWED_CHARACTERS = "[a-zA-Z0-9\\x{80}-\\x{10FFFF}\\-_ ]";
    
    /**
     * Regular expression to check the validity of a member name.
     */
    const MEMBER_NAME_REGEXP = '/^' . self::MEMBER_NAME_GLOBALLY_ALLOWED_CHARACTER_CLASS . '{1}(' . self::MEMBER_NAME_INNER_ALLOWED_CHARACTERS . '*' . self::MEMBER_NAME_GLOBALLY_ALLOWED_CHARACTER_CLASS . '{1}' . ')?$/u';
    
    /**
     * Checks whether the given member name is valid.
     *
     * Requirements:
     * - it MUST contain at least one character.
     * - it MUST contain only the allowed characters
     * - it MUST start and end with a "globally allowed character"
     *
     * @param string $member_name
     *   A member name to validate.
     *
     * @return bool
     *   Whether the given member name is in compliance with the JSON:API
     *   specification.
     *
     * @see http://jsonapi.org/format/#document-member-names
     */
    public static function isValidMemberName($member_name) {
        return preg_match(static::MEMBER_NAME_REGEXP, $member_name) === 1;
    }
    
    /**
     * The reserved (official) query parameters.
     */
    const RESERVED_QUERY_PARAMETERS = [
        'filter',
        'sort',
        'page',
        'fields',
        'include',
    ];
    
    /**
     * The query parameter for providing a version (revision) value.
     *
     * @var string
     */
    const VERSION_QUERY_PARAMETER = 'resourceVersion';
    
    /**
     * Gets the reserved (official) JSON:API query parameters.
     *
     * @return string[]
     *   Gets the query parameters reserved by the specification.
     */
    public static function getReservedQueryParameters() {
        return static::RESERVED_QUERY_PARAMETERS;
    }
    
    /**
     * Checks whether the given custom query parameter name is valid.
     *
     * A custom query parameter name must be a valid member name, with one
     * additional requirement: it MUST contain at least one non a-z character.
     *
     * Requirements:
     * - it MUST contain at least one character.
     * - it MUST contain only the allowed characters
     * - it MUST start and end with a "globally allowed character"
     * - it MUST contain at least none a-z (U+0061 to U+007A) character
     *
     * It is RECOMMENDED that a hyphen (U+002D), underscore (U+005F) or capital
     * letter is used (i.e. camelCasing).
     *
     * @param string $custom_query_parameter_name
     *   A custom query parameter name to validate.
     *
     * @return bool
     *   Whether the given query parameter is in compliance with the JSON:API
     *   specification.
     *
     * @see http://jsonapi.org/format/#query-parameters
     */
    public static function isValidCustomQueryParameter($custom_query_parameter_name) {
        return static::isValidMemberName($custom_query_parameter_name) && preg_match('/[^a-z]/u', $custom_query_parameter_name) === 1;
    }

}