<?php
/**
 * Export step 3: every prefixed table becomes two archive entries, db/<table>.schema (kind db-schema) and
 * db/<table>.jsonl (kind db-rows). Rows go to a work file in the job folder first, which is then added and deleted.
 *
 * Crash safety: the writer state and this cursor are saved together. A finished table's work file is deleted only at
 * the start of the next slice, once the cursor that records the table as added has been saved; the files finished in
 * the last slice are removed by the write-files step.
 *
 * @package Mench_Migrate
 */

defined( 'ABSPATH' ) || exit;
// phpcs:disable WordPress.WP.AlternativeFunctions -- Streams backups, uploads and job files (often several GB) chunk by chunk inside the plugin's own storage folder and the site being restored; WP_Filesystem has no streaming or locking API.

class Mench_Migrate_Step_Export_Db extends Mench_Migrate_Step_Export_Base {

	public function label(): string {
		return __( 'Exporting the database', 'mench-migrate' );
	}

	public function run( Mench_Migrate_Job $job, float $deadline ): Mench_Migrate_Step_Result {
		global $wpdb;
		if ( empty( $job->data['options']['include']['db'] ) ) {
			return Mench_Migrate_Step_Result::done( [ 'db' => [ 'tables' => 0, 'rows' => 0 ] ] );
		}
		$c = $job->cursor + [ 'tables' => null, 'est' => 0, 'i' => 0, 'phase' => 'rows', 'rows_cursor' => null, 'table_rows' => 0, 'schema' => false, 'add' => [], 'rows' => 0, 'delete' => [] ];

		foreach ( (array) $c['delete'] as $f ) {
			$path = self::db_dir( $job ) . '/' . basename( (string) $f );
			is_file( $path ) && unlink( $path );
		}
		$c['delete'] = [];

		$exporter = new Mench_Migrate_Db_Exporter( $wpdb, $wpdb->prefix );
		if ( null === $c['tables'] ) {
			$c['tables'] = $exporter->tables();
			$c['est']    = self::estimate_rows( $c['tables'] );
			foreach ( $exporter->skipped() as $view ) {
				$job->log( 'warning', 'Skipped view ' . $view . '.' );
			}
		}
		$dir = self::db_dir( $job );
		if ( ! is_dir( $dir ) && ! wp_mkdir_p( $dir ) ) {
			throw new Mench_Migrate_Storage_Exception( 'Cannot create the database work folder.', 'export-db' );
		}

		$writer = null;
		$count  = count( $c['tables'] );
		$est    = (int) ( $c['est'] ?? 0 );
		$report = static function ( int $table_rows ) use ( $job, &$c, $count, $est ): void {
			$rows = (int) $c['rows'] + $table_rows;
			Mench_Migrate_Progress::report( $job, [
				'counts'   => [ 'tables_done' => (int) $c['i'], 'tables_total' => $count, 'rows_done' => $rows ],
				'fraction' => $est > 0 ? min( 0.99, $rows / $est ) : (int) $c['i'] / max( 1, $count ),
			] );
		};
		$report( 'rows' === $c['phase'] ? (int) ( $c['rows_cursor']['rows'] ?? 0 ) : (int) $c['table_rows'] );
		while ( $c['i'] < $count ) {
			$table = (string) $c['tables'][ $c['i'] ];
			$work  = sprintf( '%05d.jsonl', $c['i'] ); // Never derived from the table name, so it cannot leave the folder.
			$file  = $dir . '/' . $work;

			if ( 'rows' === $c['phase'] ) {
				$res = $exporter->export_rows( $table, $file, $c['rows_cursor'], $deadline, $table === $wpdb->options ? [ self::class, 'keep_option' ] : null, $report );
				Mench_Migrate_Job_Runner::heartbeat( $job );
				if ( ! $res['done'] ) {
					$c['rows_cursor'] = $res['cursor'];
					break;
				}
				$c['table_rows'] = $res['rows'];
				$c['phase']      = 'add';
				if ( microtime( true ) >= $deadline ) {
					break;
				}
			}

			$writer = $writer ?? self::writer( $job );
			if ( ! $c['schema'] ) {
				$writer->add_string( 'db/' . $table . '.schema', $exporter->schema( $table ), 'db-schema' );
				$c['schema'] = true;
			}
			$res      = $writer->add_file( $file, 'db/' . $table . '.jsonl', $c['add'], $deadline, 'db-rows' );
			$c['add'] = $res['cursor'];
			Mench_Migrate_Job_Runner::heartbeat( $job );
			if ( ! $res['done'] ) {
				break;
			}
			$c['rows']      += $c['table_rows'];
			$c['delete'][]   = $work;
			$c['i']++;
			$c['phase']       = 'rows';
			$c['rows_cursor'] = null;
			$c['table_rows']  = 0;
			$c['schema']      = false;
			$c['add']         = [];
			$report( 0 );
			if ( microtime( true ) >= $deadline ) {
				break;
			}
		}
		if ( null !== $writer ) {
			$job->data['writer'] = $writer->state();
			unset( $writer );
		}

		if ( $c['i'] < $count ) {
			return Mench_Migrate_Step_Result::more( $c, $est > 0 ? min( 0.99, $c['rows'] / $est ) : $c['i'] / max( 1, $count ) );
		}
		// The last slice's work files stay until this result is saved; the write-files step removes the folder first.
		$job->log( 'info', 'Exported ' . $count . ' tables, ' . $c['rows'] . ' rows.' );
		return Mench_Migrate_Step_Result::done( [ 'db' => [ 'tables' => $count, 'rows' => $c['rows'] ] ] );
	}

	/** The server's row estimate for these tables (information_schema), only to size the progress bar. */
	private static function estimate_rows( array $tables ): int {
		global $wpdb;
		if ( ! $tables ) {
			return 0;
		}
		$in  = implode( ',', array_fill( 0, count( $tables ), '%s' ) );
		$sum = $wpdb->get_var( $wpdb->prepare( "SELECT SUM(TABLE_ROWS) FROM information_schema.TABLES WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME IN ($in)", $tables ) ); // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared,WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare,WordPress.DB.DirectDatabaseQuery
		return max( 0, (int) $sum );
	}

	/**
	 * Leaves every Mench Migrate transient (and its timeout) out of the archive: the password stash, and site-specific
	 * state such as the backup protection probe, which would make the target show the source's result.
	 */
	public static function keep_option( array $row ): bool {
		$name = (string) ( $row['option_name'] ?? '' );
		foreach ( [ '_transient_', '_transient_timeout_', '_site_transient_', '_site_transient_timeout_' ] as $prefix ) {
			if ( 0 === strpos( $name, $prefix . 'mench_migrate_' ) ) {
				return false;
			}
		}
		return true;
	}
}