<?php
/**
 * Drops staging tables that a transfer left on this database.
 *
 * @package Shiftora\Migration
 */

declare(strict_types=1);

namespace Shiftora\Migration;

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

/**
 * Staging tables ({prefix}shiftora_stg_{token}_{bare}) hold a copy of the incoming
 * data, so one left behind by a failed or abandoned transfer keeps eating the disk
 * the next attempt needs. Every drop goes through SHOW TABLES and an exact name
 * check, so a LIKE pattern can never widen it to a neighbour.
 */
final class StagingSweeper {

	/** Orphans younger than this may belong to an import that is still writing. */
	public const MIN_ORPHAN_AGE = DAY_IN_SECONDS;

	public function __construct( private readonly \wpdb $wpdb ) {}

	/**
	 * Drops staging tables nobody owns and nothing has touched for a day.
	 *
	 * Age comes from the table's create time. A table whose age cannot be read is
	 * kept, since dropping a live import's table costs more than keeping a dead one.
	 *
	 * @param string[] $live_names Staging names a live lease plans.
	 *
	 * @return string[] Dropped names.
	 */
	public function sweep_stale( array $live_names, int $min_age_seconds = self::MIN_ORPHAN_AGE ): array {
		$live    = array_flip( array_map( 'strval', $live_names ) );
		$ages    = $this->ages();
		$dropped = [];

		foreach ( $this->staged_tables() as $table ) {
			if ( isset( $live[ $table ] ) || ! isset( $ages[ $table ] ) || $ages[ $table ] < $min_age_seconds ) {
				continue;
			}

			$this->drop( $table );
			$dropped[] = $table;
		}

		return $dropped;
	}

	/** @return string[] Staging tables that exist, each checked against the exact stem. */
	private function staged_tables(): array {
		$stem = (string) $this->wpdb->prefix . 'shiftora_stg_';

		$wpdb  = $this->wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- server metadata, nothing to cache
		$found = (array) $wpdb->get_col(
			$wpdb->prepare( 'SHOW TABLES LIKE %s', $wpdb->esc_like( $stem ) . '%' )
		);

		return array_values( array_filter(
			array_map( 'strval', $found ),
			static fn( string $table ): bool => str_starts_with( $table, $stem )
		) );
	}

	/** @return array<string, int> Seconds since each staging table was created, per the server's own clock. */
	private function ages(): array {
		$wpdb = $this->wpdb;
		$stem = (string) $wpdb->prefix . 'shiftora_stg_';

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- server metadata, nothing to cache
		$rows = (array) $wpdb->get_results(
			$wpdb->prepare(
				'SELECT TABLE_NAME, TIMESTAMPDIFF( SECOND, CREATE_TIME, NOW() ) AS age
				   FROM information_schema.TABLES
				  WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME LIKE %s AND CREATE_TIME IS NOT NULL',
				$wpdb->esc_like( $stem ) . '%'
			),
			ARRAY_A
		);

		$ages = [];
		foreach ( $rows as $row ) {
			if ( isset( $row['TABLE_NAME'], $row['age'] ) && is_numeric( $row['age'] ) ) {
				$ages[ (string) $row['TABLE_NAME'] ] = (int) $row['age'];
			}
		}

		return $ages;
	}

	private function drop( string $table ): void {
		$wpdb = $this->wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- the transfer reads and writes the site's own tables, a cached copy would be stale
		$wpdb->query( $wpdb->prepare( 'DROP TABLE IF EXISTS %i', $table ) );
	}
}