<?php
/**
 * Session sql_mode in and out around raw SQL that came from another site.
 *
 * @package Shiftora\Support
 */

declare(strict_types=1);

namespace Shiftora\Support;

use Shiftora\Support\Db\SqlLiteral;

// Prevent direct file access.
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Relaxes the session sql_mode while foreign statements run, then restores it.
 *
 * A strict session rejects data a legacy source legitimately holds, such as a
 * `0000-00-00` default (ERROR 1067) or zero-date row (ERROR 1292). The
 * connection outlives the import, so restore() must run on every exit or later
 * queries stay weakened.
 */
final class SessionSqlMode {

	/**
	 * The mode foreign statements run under: non-strict so zero-dates pass, and
	 * NO_AUTO_VALUE_ON_ZERO so a literal `0` in an auto-increment column is kept.
	 */
	private const RELAXED = 'NO_AUTO_VALUE_ON_ZERO';

	/** How many relax() calls are open on the held connection; only the outermost touches the server. */
	private static int $depth = 0;

	/** The connection the open relax() calls belong to. */
	private static ?\WeakReference $held = null;

	/** What the outermost relax() read, handed back to every nested caller. */
	private static string $held_previous = '';

	/**
	 * Relaxes the session and returns the previous mode ('' when unreadable).
	 *
	 * Throws only when the session still escapes quotes alone afterwards; nothing has
	 * changed then, so there is nothing to restore.
	 *
	 * Calls nest: a batch relaxes once around many chunks, and the chunks inside it
	 * cost no queries. Each relax() needs its own restore().
	 */
	public static function relax( \wpdb $wpdb ): string {
		if ( self::$depth > 0 && self::$held?->get() === $wpdb ) {
			++self::$depth;

			return self::$held_previous;
		}

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- a session setting, nothing to cache
		$previous = (string) ( $wpdb->get_var( 'SELECT @@SESSION.sql_mode' ) ?? '' );

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- a session setting, nothing to cache
		$wpdb->query( $wpdb->prepare( 'SET SESSION sql_mode = %s', self::RELAXED ) );

		// Read back rather than assume: the SET can miss, or land on another connection.
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- a session setting, nothing to cache
		$now = (string) ( $wpdb->get_var( 'SELECT @@SESSION.sql_mode' ) ?? '' );
		SqlLiteral::session_mode_changed( $wpdb, $now );

		if ( str_contains( strtoupper( $now ), 'NO_BACKSLASH_ESCAPES' ) ) {
			throw new \RuntimeException( 'The database session kept NO_BACKSLASH_ESCAPES after it was asked to drop it, so SQL cannot be written for the other site safely.' );
		}

		self::$depth         = 1;
		self::$held          = \WeakReference::create( $wpdb );
		self::$held_previous = $previous;

		return $previous;
	}

	/**
	 * Puts back what relax() returned. The shape check keeps anything but a comma
	 * list of mode names out of the built query. Never throws; callers are finally blocks.
	 */
	public static function restore( \wpdb $wpdb, string $previous ): void {
		if ( self::$depth > 1 && self::$held?->get() === $wpdb ) {
			--self::$depth;

			return;
		}

		self::$depth = 0;
		self::$held  = null;

		if ( ! preg_match( '/^[A-Za-z0-9_, ]*$/', $previous ) ) {
			$previous = '';
		}

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- a session setting, nothing to cache
		$wpdb->query( $wpdb->prepare( 'SET SESSION sql_mode = %s', $previous ) );
		SqlLiteral::session_mode_changed( $wpdb );
	}
}