<?php
/**
 * Read-only facts about a site's MySQL and PHP environment.
 *
 * @package Shiftora\Support
 */

declare(strict_types=1);

namespace Shiftora\Support;

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

/**
 * Server facts that decide whether a migration between two sites will behave:
 * MySQL flavor and version, packet ceiling, sql_mode, table-name case folding,
 * charset and PHP limits. Exchanged over the authenticated handshake so each
 * side can check the other before data moves.
 */
final class ServerCapabilities {

	/**
	 * Probes the current site. Every field is best-effort: a failed query leaves
	 * it null or empty, which callers treat as "unknown".
	 *
	 * @return array{
	 *   mysql_version: string,
	 *   is_mariadb: bool,
	 *   numeric_version: string,
	 *   max_allowed_packet: int,
	 *   sql_mode: string,
	 *   lower_case_table_names: int|null,
	 *   server_charset: string,
	 *   server_collation: string,
	 *   php_memory_limit: int,
	 *   max_execution_time: int
	 * }
	 */
	public static function probe( \wpdb $wpdb ): array {
		$raw_version = (string) $wpdb->get_var( 'SELECT VERSION()' ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery -- SELECT VERSION() reads server metadata that no WordPress API exposes.
		$is_mariadb  = self::is_mariadb_version( $raw_version );

		// MariaDB prefixes a fake "5.5.5-" ahead of its real version.
		$clean   = (string) preg_replace( '/^5\.5\.5-/', '', $raw_version );
		$numeric = (string) preg_replace( '/[^0-9.].*/', '', $clean );

		return [
			'mysql_version'          => $clean,
			'is_mariadb'             => $is_mariadb,
			'numeric_version'        => $numeric,
			'max_allowed_packet'     => (int) self::variable( $wpdb, 'max_allowed_packet' ),
			'sql_mode'               => (string) self::variable( $wpdb, 'sql_mode' ),
			'lower_case_table_names' => self::int_variable( $wpdb, 'lower_case_table_names' ),
			'server_charset'         => (string) self::variable( $wpdb, 'character_set_server' ),
			'server_collation'       => (string) self::variable( $wpdb, 'collation_server' ),
			'php_memory_limit'       => self::bytes_from_ini( (string) ini_get( 'memory_limit' ) ),
			'max_execution_time'     => (int) ini_get( 'max_execution_time' ),
		];
	}

	/** Whether a SELECT VERSION() string comes from MariaDB. */
	public static function is_mariadb_version( string $raw_version ): bool {
		return false !== stripos( $raw_version, 'mariadb' );
	}

	/** One MySQL variable value, or '' when unreadable. */
	private static function variable( \wpdb $wpdb, string $name ): string {
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- a server variable, nothing to cache
		$row = $wpdb->get_row( $wpdb->prepare( 'SHOW VARIABLES LIKE %s', $wpdb->esc_like( $name ) ), ARRAY_N );

		return is_array( $row ) && isset( $row[1] ) ? (string) $row[1] : '';
	}

	/** One variable as an int, or null when unreported, so "zero" differs from "unknown". */
	private static function int_variable( \wpdb $wpdb, string $name ): ?int {
		$value = self::variable( $wpdb, $name );

		return '' === $value ? null : (int) $value;
	}

	/** A PHP ini size ('256M', '1G') in bytes; -1 and 0 (no limit) become 0. */
	private static function bytes_from_ini( string $value ): int {
		$value = trim( $value );
		if ( '' === $value || '-1' === $value ) {
			return 0;
		}

		$unit   = strtolower( $value[ strlen( $value ) - 1 ] );
		$number = (int) $value;

		return match ( $unit ) {
			'g'     => $number * 1024 * 1024 * 1024,
			'm'     => $number * 1024 * 1024,
			'k'     => $number * 1024,
			default => max( 0, (int) $value ),
		};
	}
}