<?php
/**
 * Cookieless visitor identity.
 *
 * visitor_hash = HMAC-SHA1( daily_salt , site_host . "|" . ip . "|" . ua )
 *
 * The daily salt is 32 random bytes, regenerated every calendar day (site
 * timezone) and NOT retained beyond "current" + "previous" day. Because the
 * salt is thrown away, yesterday's hashes can never be recomputed or linked
 * to today's — a visitor cannot be followed across days and cannot be
 * re-identified from the stored hash. This is the Fathom/Plausible model.
 *
 * The raw IP is used only to build the hash and for the GeoIP lookup; it is
 * never written to the database.
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

class SXANL_Visitor {

	const SALT_OPTION = 'sxanl_visitor_salt';

	/**
	 * Compute the visitor hash for the current request.
	 *
	 * @param string $ip Client IP.
	 * @param string $ua Client user-agent.
	 * @return string 40-char hex
	 */
	public static function hash( $ip, $ua ) {
		$salt = self::current_salt();
		$data = sxanl_site_host() . '|' . $ip . '|' . $ua;
		return hash_hmac( 'sha1', $data, $salt );
	}

	/**
	 * Was this visitor already seen today? (Used to flag new vs returning.)
	 * Checks only against today's rows, so it stays cookieless and cheap.
	 *
	 * @param string $visitor_hash Hash for this request.
	 * @return bool
	 */
	public static function seen_today( $visitor_hash ) {
		global $wpdb;
		$sessions = SXANL_Schema::table( 'sessions' );
		$today    = sxanl_site_date();
		$exists   = $wpdb->get_var(
			$wpdb->prepare(
				"SELECT 1 FROM $sessions WHERE day = %s AND visitor_hash = %s LIMIT 1", // phpcs:ignore WordPress.DB.PreparedSQL
				$today,
				$visitor_hash
			)
		);
		return (bool) $exists;
	}

	/**
	 * Current day's salt, creating/rotating it if the day has turned.
	 *
	 * @return string
	 */
	private static function current_salt() {
		$store = get_option( self::SALT_OPTION );
		$today = sxanl_site_date();

		if ( is_array( $store ) && isset( $store['day'], $store['salt'] ) && $store['day'] === $today ) {
			return (string) $store['salt'];
		}
		return self::rotate_salt();
	}

	/**
	 * Generate a new salt for today, keeping yesterday's only long enough for
	 * an in-flight request boundary, then persist.
	 *
	 * @return string the new salt
	 */
	public static function rotate_salt() {
		$today = sxanl_site_date();
		$salt  = bin2hex( self::random_bytes( 32 ) );
		$prev  = get_option( self::SALT_OPTION );

		$store = array(
			'day'       => $today,
			'salt'      => $salt,
			'prev_day'  => is_array( $prev ) && isset( $prev['day'] ) ? $prev['day'] : '',
			'prev_salt' => is_array( $prev ) && isset( $prev['salt'] ) ? $prev['salt'] : '',
		);
		update_option( self::SALT_OPTION, $store, false );
		SXANL_Settings::update( array( 'hash_salt_rotated' => $today ) );
		return $salt;
	}

	/**
	 * Random bytes with graceful fallback.
	 *
	 * @param int $len Bytes.
	 * @return string
	 */
	private static function random_bytes( $len ) {
		try {
			return random_bytes( $len );
		} catch ( \Exception $e ) {
			return wp_generate_password( $len, true, true );
		}
	}
}