<?php
/**
 * TMDO_Snapshot_Writer — produces a SQL dump of WPDO tables (v2.2.0 M1).
 *
 * Strategy:
 *   1. Resolve which tables to dump from the scope (default = all WPDO-owned tables).
 *   2. Iterate each table in 5000-row chunks; emit `INSERT INTO ... VALUES (...)`.
 *   3. Stream output to a temp file with gzip; compute sha256 and final size.
 *   4. If final size ≤ INLINE_THRESHOLD_BYTES, slurp into memory + delete file
 *      (so small snapshots travel with `wp db export`).
 *   5. Otherwise leave the file under wp-content/uploads/wpdo-backups/.
 *
 * @package WP_Data_Optimizer
 */

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

/**
 * Streamed dump writer with chunking + gzip + sha256.
 */
class TMDO_Snapshot_Writer {

	/** Rows per SELECT chunk. */
	private const CHUNK_SIZE = 5000;

	/**
	 * Snapshot ULID assigned by manager.
	 *
	 * @var string
	 */
	private string $snapshot_id;

	/**
	 * Resolved dump scope.
	 *
	 * @var array{entities:array,modules:array,tables:array}
	 */
	private array $scope;

	/**
	 * Writer options (gzip, inline_threshold_bytes, max_tables).
	 *
	 * @var array<string,mixed>
	 */
	private array $opts;

	/**
	 * Constructor.
	 *
	 * @param string $snapshot_id Snapshot ULID.
	 * @param array  $scope       Resolved scope.
	 * @param array  $opts        {gzip:bool, inline_threshold_bytes:int, max_tables:int}.
	 */
	public function __construct( string $snapshot_id, array $scope, array $opts = array() ) {
		$this->snapshot_id = $snapshot_id;
		$this->scope       = $scope;
		$this->opts        = $opts;
	}

	/**
	 * Run the dump.
	 *
	 * @return array {storage,file_path,sha256,size_bytes,row_count,inline_blob}
	 * @throws RuntimeException When no tables resolved or filesystem unwritable.
	 */
	public function write(): array {
		$tables = $this->resolve_tables();
		if ( empty( $tables ) ) {
			throw new RuntimeException( 'snapshot scope produced 0 tables' );
		}

		$gzip      = (bool) ( $this->opts['gzip'] ?? true );
		$inline_th = (int) ( $this->opts['inline_threshold_bytes'] ?? TMDO_Snapshot_Manager::INLINE_THRESHOLD_BYTES );
		$dir       = TMDO_Snapshot_Manager::backup_dir();
		$ext       = $gzip ? '.sql.gz' : '.sql';
		$path      = trailingslashit( $dir ) . $this->snapshot_id . $ext;

		$handle = $gzip ? gzopen( $path, 'wb6' ) : fopen( $path, 'wb' );
		if ( false === $handle ) {
			throw new RuntimeException( 'cannot open ' . $path . ' for write' ); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- exception message, not HTML output
		}
		$write = static function ( string $chunk ) use ( $handle, $gzip ): void {
			if ( $gzip ) {
				gzwrite( $handle, $chunk );
			} else {
				fwrite( $handle, $chunk );
			}
		};

		$row_count = 0;
		$header    = $this->dump_header( $tables );
		$write( $header );

		global $wpdb;
		foreach ( $tables as $table ) {
			$row_count += $this->dump_table( $table, $write );
		}
		$write( "\n-- end of dump\n" );

		if ( $gzip ) {
			gzclose( $handle );
		} else {
			fclose( $handle );
		}

		$size = (int) filesize( $path );
		$sha  = hash_file( 'sha256', $path );

		// Decide inline vs file storage.
		if ( $size <= $inline_th ) {
			$blob = file_get_contents( $path );
			@unlink( $path ); // phpcs:ignore WordPress.PHP.NoSilencedErrors
			return array(
				'storage'     => 'inline',
				'file_path'   => null,
				'sha256'      => $sha,
				'size_bytes'  => $size,
				'row_count'   => $row_count,
				'inline_blob' => $blob,
			);
		}

		return array(
			'storage'     => 'file',
			'file_path'   => $path,
			'sha256'      => $sha,
			'size_bytes'  => $size,
			'row_count'   => $row_count,
			'inline_blob' => null,
		);
	}

	/**
	 * Returns canonical scope (after manager resolution).
	 *
	 * @return array
	 */
	public function get_scope(): array {
		return $this->scope;
	}

	// ─── private ──────────────────────────────────────────────────────────

	/**
	 * Resolve which tables to dump.
	 *
	 * Priority:
	 *   1. Explicit `scope.tables` if provided.
	 *   2. `scope.entities` → wp_postmeta / wp_usermeta / etc.
	 *   3. Empty scope → all WPDO-owned tables (zone + system) + wp_postmeta if classifier active.
	 *
	 * @return array<int,string> Fully-prefixed table names.
	 */
	private function resolve_tables(): array {
		global $wpdb;
		if ( ! empty( $this->scope['tables'] ) ) {
			return array_values( array_filter( array_map( 'strval', $this->scope['tables'] ), array( $this, 'is_safe_name' ) ) );
		}

		$max = (int) ( $this->opts['max_tables'] ?? 200 );
		$out = array();

		// Always include WPDO system tables.
		$wpdo_likes = array(
			$wpdb->prefix . 'wpdo_%',
		);
		foreach ( $wpdo_likes as $like ) {
			if ( class_exists( 'WP_SQLite_Driver' ) ) {
				$rows = $wpdb->get_col(
					$wpdb->prepare( // phpcs:ignore WordPress.DB
						"SELECT name FROM sqlite_master WHERE type='table' AND name LIKE %s",
						$like
					)
				);
			} else {
				$rows = $wpdb->get_col(
					$wpdb->prepare( // phpcs:ignore WordPress.DB
						'SELECT TABLE_NAME FROM information_schema.TABLES WHERE TABLE_SCHEMA = DATABASE() AND TABLE_NAME LIKE %s',
						$like
					)
				);
			}
			if ( is_array( $rows ) ) {
				foreach ( $rows as $t ) {
					if ( $this->is_safe_name( (string) $t ) ) {
						$out[ $t ] = true;
					}
				}
			}
		}

		// Skip wp_wpdo_snapshots itself — we don't want a dump of a dump.
		unset( $out[ $wpdb->prefix . 'wpdo_snapshots' ] );

		// If `entities` includes 'post', also dump wp_postmeta (mainly used for
		// pre_v2_upgrade trigger so we have the pre-migration meta).
		if ( ! empty( $this->scope['entities'] ) ) {
			$entity_to_table = array(
				'post'    => $wpdb->postmeta,
				'user'    => $wpdb->usermeta,
				'term'    => $wpdb->termmeta ?? ( $wpdb->prefix . 'termmeta' ),
				'comment' => $wpdb->commentmeta,
			);
			foreach ( $this->scope['entities'] as $entity ) {
				if ( isset( $entity_to_table[ $entity ] ) ) {
					$t = $entity_to_table[ $entity ];
					if ( $this->is_safe_name( $t ) ) {
						$out[ $t ] = true;
					}
				}
			}
		}

		$tables = array_keys( $out );
		if ( count( $tables ) > $max ) {
			$tables = array_slice( $tables, 0, $max );
		}
		sort( $tables );
		return $tables;
	}

	/**
	 * Validate a table name (alphanumeric + underscore only, must start with $wpdb->prefix).
	 *
	 * @param string $name Table name.
	 * @return bool
	 */
	private function is_safe_name( string $name ): bool {
		global $wpdb;
		return (bool) preg_match( '/^[a-zA-Z0-9_]+$/', $name )
			&& strpos( $name, $wpdb->prefix ) === 0;
	}

	/**
	 * Dump header (timestamp + table list).
	 *
	 * @param array $tables Tables that will be dumped.
	 * @return string
	 */
	private function dump_header( array $tables ): string {
		$out  = "-- WPDO snapshot {$this->snapshot_id}\n";
		$out .= '-- Generated: ' . gmdate( 'Y-m-d H:i:s' ) . " UTC\n";
		$out .= '-- Tables: ' . count( $tables ) . "\n";
		$out .= "-- Format: SQL INSERT statements (one per row, batched by table)\n\n";
		$out .= "SET NAMES utf8mb4;\n";
		$out .= "SET FOREIGN_KEY_CHECKS=0;\n\n";
		return $out;
	}

	/**
	 * Stream-dump one table.
	 *
	 * @param string   $table Fully-prefixed table name.
	 * @param callable $write Stream writer.
	 * @return int rows dumped.
	 */
	private function dump_table( string $table, callable $write ): int {
		global $wpdb;

		$write( "-- Table {$table}\n" );
		$count_total = (int) $wpdb->get_var( "SELECT COUNT(*) FROM `{$table}`" ); // phpcs:ignore WordPress.DB
		if ( 0 === $count_total ) {
			$write( "-- (empty)\n\n" );
			return 0;
		}

		$columns = $wpdb->get_col( "DESC `{$table}`" ); // phpcs:ignore WordPress.DB
		if ( ! is_array( $columns ) || empty( $columns ) ) {
			return 0;
		}
		$col_list = '`' . implode( '`,`', $columns ) . '`';

		$offset      = 0;
		$rows_dumped = 0;
		while ( $offset < $count_total ) {
			$chunk = $wpdb->get_results(
				$wpdb->prepare( // phpcs:ignore WordPress.DB
					"SELECT * FROM `{$table}` LIMIT %d OFFSET %d", // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared -- {$table} is a trusted table name via TMDO_DB::table()
					self::CHUNK_SIZE,
					$offset
				),
				ARRAY_A
			);
			if ( ! is_array( $chunk ) || empty( $chunk ) ) {
				break;
			}
			$values = array();
			foreach ( $chunk as $row ) {
				$row_vals = array();
				foreach ( $columns as $col ) {
					$row_vals[] = $this->escape_sql_value( $row[ $col ] ?? null );
				}
				$values[] = '(' . implode( ',', $row_vals ) . ')';
			}
			$write( "INSERT INTO `{$table}` ({$col_list}) VALUES " . implode( ",\n  ", $values ) . ";\n" );
			$rows_dumped += count( $chunk );
			$offset      += self::CHUNK_SIZE;
		}
		$write( "\n" );
		return $rows_dumped;
	}

	/**
	 * Escape a single value for SQL INSERT.
	 *
	 * @param mixed $v Value.
	 * @return string SQL-quoted literal.
	 */
	private function escape_sql_value( $v ): string {
		global $wpdb;
		if ( null === $v ) {
			return 'NULL';
		}
		if ( is_bool( $v ) ) {
			return $v ? '1' : '0';
		}
		if ( is_int( $v ) || is_float( $v ) ) {
			return (string) $v;
		}
		// String / longtext / blob — wrap with hex notation if non-utf8 bytes.
		$s = (string) $v;
		// Use mb_check_encoding when available; fall back to a heuristic.
		$is_utf8 = function_exists( 'mb_check_encoding' ) ? mb_check_encoding( $s, 'UTF-8' ) : ( @iconv( 'UTF-8', 'UTF-8//IGNORE', $s ) === $s ); // phpcs:ignore WordPress.PHP.NoSilencedErrors
		if ( ! $is_utf8 ) {
			return '0x' . bin2hex( $s );
		}
		return "'" . esc_sql( $s ) . "'";
	}
}