<?php
/**
 * Validation helpers for French company identifiers.
 *
 * - SIREN: 9 digits, Luhn checksum.
 * - SIRET: 14 digits (SIREN + 5-digit establishment number), Luhn checksum.
 *   Exception: La Poste establishments (SIREN 356000000) use a digit-sum rule.
 * - French VAT number: "FR" + 2-character key + SIREN.
 *   Numeric key = (12 + 3 * (SIREN mod 97)) mod 97.
 *
 * This class has no WordPress dependency so it can be unit tested in isolation.
 *
 * @package EFactureFR
 */

defined( 'ABSPATH' ) || exit;

/**
 * Identifier validation.
 */
class EFacture_FR_Identifiers {

	/**
	 * Remove spaces, dots and dashes that people type for readability.
	 *
	 * @param string $value Raw input.
	 * @return string
	 */
	public static function normalize( $value ) {
		return strtoupper( preg_replace( '/[\s.\-]/', '', (string) $value ) );
	}

	/**
	 * Luhn checksum over a string of digits.
	 *
	 * @param string $digits Digits only.
	 * @return bool
	 */
	public static function luhn( $digits ) {
		$sum    = 0;
		$length = strlen( $digits );
		for ( $i = 0; $i < $length; $i++ ) {
			$digit = (int) $digits[ $length - 1 - $i ];
			if ( 1 === $i % 2 ) {
				$digit *= 2;
				if ( $digit > 9 ) {
					$digit -= 9;
				}
			}
			$sum += $digit;
		}
		return 0 === $sum % 10;
	}

	/**
	 * Validate a SIREN number.
	 *
	 * @param string $value Raw input.
	 * @return bool
	 */
	public static function is_valid_siren( $value ) {
		$value = self::normalize( $value );
		return (bool) preg_match( '/^\d{9}$/', $value ) && self::luhn( $value );
	}

	/**
	 * Validate a SIRET number.
	 *
	 * @param string $value Raw input.
	 * @return bool
	 */
	public static function is_valid_siret( $value ) {
		$value = self::normalize( $value );
		if ( ! preg_match( '/^\d{14}$/', $value ) ) {
			return false;
		}
		if ( self::luhn( $value ) ) {
			return true;
		}
		// Many La Poste establishments do not pass Luhn; their digit sum is a multiple of 5 instead.
		return '356000000' === substr( $value, 0, 9 ) && 0 === array_sum( str_split( $value ) ) % 5;
	}

	/**
	 * Compute the French VAT number for a SIREN.
	 *
	 * @param string $siren Valid SIREN.
	 * @return string e.g. FR40303265045
	 */
	public static function vat_from_siren( $siren ) {
		$siren = self::normalize( $siren );
		$key   = ( 12 + 3 * ( (int) $siren % 97 ) ) % 97;
		return 'FR' . str_pad( (string) $key, 2, '0', STR_PAD_LEFT ) . $siren;
	}

	/**
	 * Validate a French VAT number.
	 *
	 * Numeric keys are checked against the SIREN. Alphanumeric keys (issued to
	 * some companies) are accepted on format only.
	 *
	 * @param string $value Raw input.
	 * @return bool
	 */
	public static function is_valid_fr_vat( $value ) {
		$value = self::normalize( $value );
		if ( ! preg_match( '/^FR([0-9A-HJ-NP-Z]{2})(\d{9})$/', $value, $m ) ) {
			return false;
		}
		if ( ctype_digit( $m[1] ) ) {
			return self::vat_from_siren( $m[2] ) === $value;
		}
		return true;
	}

	/**
	 * Basic format check for EU VAT numbers outside France (2-letter prefix + 2-13 chars).
	 *
	 * @param string $value Raw input.
	 * @return bool
	 */
	public static function looks_like_eu_vat( $value ) {
		$value = self::normalize( $value );
		if ( 0 === strpos( $value, 'FR' ) ) {
			return self::is_valid_fr_vat( $value );
		}
		return (bool) preg_match( '/^(AT|BE|BG|CY|CZ|DE|DK|EE|EL|ES|FI|HR|HU|IE|IT|LT|LU|LV|MT|NL|PL|PT|RO|SE|SI|SK|XI)[0-9A-Z]{2,13}$/', $value );
	}

	/**
	 * Return the SIREN contained in a SIRET.
	 *
	 * @param string $siret Valid SIRET.
	 * @return string
	 */
	public static function siren_from_siret( $siret ) {
		return substr( self::normalize( $siret ), 0, 9 );
	}
}