No cache.
	 *
	 * @return void
	 */
	public static function no_cache() {
		// @link https://github.com/woothemes/woocommerce/blob/2.3.11/includes/class-wc-cache-helper.php
		// @link https://www.w3-edge.com/products/w3-total-cache/
		$do_not_constants = array(
			'DONOTCACHEPAGE',
			'DONOTCACHEDB',
			'DONOTMINIFY',
			'DONOTCDN',
			'DONOTCACHEOBJECT',
		);

		foreach ( $do_not_constants as $do_not_constant ) {
			if ( ! defined( $do_not_constant ) ) {
				define( $do_not_constant, true );
			}
		}

		nocache_headers();
	}

	/**
	 * Amount to cents.
	 *
	 * @param float $amount The amount to conver to cents.
	 *
	 * @deprecated 2.0.9 Use \Pronamic\WordPress\Money\Money::get_cents() instead.
	 *
	 * @return float
	 */
	public static function amount_to_cents( $amount ) {
		_deprecated_function( __FUNCTION__, '2.0.9', 'Pronamic\WordPress\Money\Money::get_cents()' );

		$money = new Money( $amount );

		return $money->get_cents();
	}

	/**
	 * Cents to amount.
	 *
	 * @param int $cents The cents to convert to float value.
	 *
	 * @return float
	 */
	public static function cents_to_amount( $cents ) {
		return $cents / 100;
	}

	/**
	 * String to amount (user input string).
	 *
	 * @link https://github.com/WordPress/WordPress/blob/4.9.6/wp-includes/functions.php#L206-L237
	 *
	 * @version 1.3.1
	 * @since 1.3.0
	 * @deprecated 2.0.3 Use Pronamic\WordPress\Money\Parser::parse( $amount )->get_amount() instead.
	 *
	 * @param string $value The string value to convert to a float value.
	 *
	 * @return float
	 */
	public static function string_to_amount( $value ) {
		_deprecated_function( __FUNCTION__, '2.0.3', 'Pronamic\WordPress\Money\Parser::parse()->get_value()' );

		$money_parser = new MoneyParser();

		try {
			$amount = $money_parser->parse( $value )->get_value();
		} catch ( \Exception $e ) {
			$amount = (float) 0;
		}

		return $amount;
	}

	/**
	 * String to interval period (user input string).
	 *
	 * @since 2.0.3
	 * @param string $interval Interval user input string.
	 * @return string|null
	 */
	public static function string_to_interval_period( $interval ) {
		if ( ! is_string( $interval ) ) {
			return null;
		}

		$interval = trim( $interval );

		// Check last character for period.
		$interval_char = strtoupper( substr( $interval, - 1, 1 ) );

		if ( in_array( $interval_char, array( 'D', 'W', 'M', 'Y' ), true ) ) {
			return $interval_char;
		}

		// Find interval period by counting string replacements.
		$periods = array(
			'D' => array( 'D', 'day' ),
			'W' => array( 'W', 'week' ),
			'M' => array( 'M', 'month' ),
			'Y' => array( 'Y', 'year' ),
		);

		foreach ( $periods as $interval_period => $search ) {
			$count = 0;

			str_ireplace( $search, '', $interval, $count );

			if ( $count > 0 ) {
				return $interval_period;
			}
		}

		return null;
	}

	/**
	 * Convert boolean to an numeric boolean.
	 *
	 * @link https://github.com/eet-nu/buckaroo-ideal/blob/master/lib/buckaroo-ideal/request.rb#L136
	 *
	 * @param boolean $boolean The boolean value to convert to an integer value.
	 *
	 * @return int
	 */
	public static function boolean_to_numeric( $boolean ) {
		return $boolean ? 1 : 0;
	}

	/**
	 * Convert boolean to an string boolean
	 *
	 * @link https://github.com/eet-nu/buckaroo-ideal/blob/master/lib/buckaroo-ideal/request.rb#L136
	 *
	 * @param bool $boolean The boolean value to convert to a string value.
	 * @return string
	 */
	public static function boolean_to_string( $boolean ) {
		return $boolean ? 'true' : 'false';
	}

	/**
	 * Convert the specified period to a single char notation.
	 *
	 * @since 1.3.9
	 *
	 * @param string $period The period value to convert to a single character/string value.
	 *
	 * @return string
	 */
	public static function to_period( $period ) {
		if ( false !== strpos( $period, 'day' ) || false !== strpos( $period, 'daily' ) ) {
			return 'D';
		}

		if ( false !== strpos( $period, 'week' ) ) {
			return 'W';
		}

		if ( false !== strpos( $period, 'month' ) ) {
			return 'M';
		}

		if ( false !== strpos( $period, 'year' ) ) {
			return 'Y';
		}

		return $period;
	}

	/**
	 * Build URL with the specified parameters
	 *
	 * @param string $url        URL to extend with the specified parameters.
	 * @param array  $parameters URL parameters.
	 *
	 * @return string
	 */
	public static function build_url( $url, array $parameters ) {
		return $url . '?' . _http_build_query( $parameters, null, '&' );
	}

	/**
	 * Get remote address.
	 *
	 * @link https://github.com/WordPress/WordPress/blob/4.9.8/wp-admin/includes/class-wp-community-events.php#L210-L274
	 * @since 2.1.0
	 * @return mixed|null
	 */
	public static function get_remote_address() {
		// In order of preference, with the best ones for this purpose first.
		$headers = array(
			'HTTP_CLIENT_IP',
			'HTTP_X_FORWARDED_FOR',
			'HTTP_X_FORWARDED',
			'HTTP_X_CLUSTER_CLIENT_IP',
			'HTTP_FORWARDED_FOR',
			'HTTP_FORWARDED',
			'REMOTE_ADDR',
		);

		foreach ( $headers as $header ) {
			if ( isset( $_SERVER[ $header ] ) ) {
				/*
				 * HTTP_X_FORWARDED_FOR can contain a chain of comma-separated
				 * addresses. The first one is the original client. It can't be
				 * trusted for authenticity, but we don't need to for this purpose.
				 */
				$addresses = explode( ',', (string) filter_var( wp_unslash( $_SERVER[ $header ] ) ) );

				$addresses = array_slice( $addresses, 0, 1 );

				foreach ( $addresses as $address ) {
					$address = trim( $address );

					$address = filter_var( $address, FILTER_VALIDATE_IP );

					if ( false === $address ) {
						continue;
					}

					return $address;
				}
			}
		}

		return null;
	}

	/**
	 * Convert input fields array to HTML.
	 *
	 * @param array $fields Array with fields data to convert to HTML.
	 *
	 * @return string
	 */
	public static function input_fields_html( array $fields ) {
		$html = '';

		foreach ( $fields as $field ) {
			if ( ! isset( $field['type'], $field['name'] ) ) {
				continue;
			}

			$field = \wp_parse_args(
				$field,
				array(
					'id'       => $field['name'],
					'type'     => 'text',
					'value'    => ( \filter_has_var( INPUT_POST, $field['name'] ) ? \filter_input( INPUT_POST, $field['name'], FILTER_SANITIZE_STRING ) : null ),
					'required' => false,
					'max'      => null,
				)
			);

			// Field label.
			$html .= sprintf(
				'<label for="%s">%s</label> ',
				esc_attr( $field['id'] ),
				$field['label']
			);

			switch ( $field['type'] ) {
				case 'select':
					$html .= sprintf(
						'<select id="%s" name="%s" %s>%s</select>',
						esc_attr( $field['id'] ),
						esc_attr( $field['name'] ),
						( $field['required'] ? 'required' : null ),
						Pay_Util::select_options_grouped( $field['choices'] )
					);

					break;
				default:
					$attributes = array(
						'type'     => $field['type'],
						'id'       => $field['id'],
						'name'     => $field['name'],
						'value'    => $field['value'],
						'max'      => $field['max'],
						'required' => $field['required'],
					);

					$html .= sprintf( '<input %s>', Pay_Util::array_to_html_attributes( $attributes ) );

					break;
			}
		}

		return $html;
	}

	/**
	 * Method exists
	 *
	 * This helper function was created to fix an issue with `method_exists` calls
	 * and non existings classes.
	 *
	 * @param string $class  Class name to check for the specifiekd method.
	 * @param string $method Method name to check for existance.
	 *
	 * @return boolean
	 */
	public static function class_method_exists( $class, $method ) {
		return class_exists( $class ) && method_exists( $class, $method );
	}

	/**
	 * Check if input type has vars.
	 *
	 * @param int   $type           One of INPUT_GET, INPUT_POST, INPUT_COOKIE, INPUT_SERVER, or INPUT_ENV.
	 * @param array $variable_names Array of variable names to check in input type.
	 *
	 * @return bool
	 */
	public static function input_has_vars( $type, $variable_names ) {
		foreach ( $variable_names as $variable_name ) {
			if ( ! filter_has_var( $type, $variable_name ) ) {
				return false;
			}
		}

		return true;
	}
}