<?php
/**
 * TMDO_Snapshot_Reader — preview, verify, and apply a stored snapshot
 * (v2.2.0 M1).
 *
 * Loading order:
 *   1. Read catalog row from wp_wpdo_snapshots (passed in by manager).
 *   2. If `inline_blob`, decompress in-memory.
 *   3. Else read file from disk + verify sha256 + ungzip.
 *   4. Parse SQL into tables and INSERT statements.
 *   5. preview() returns parse summary; apply() executes statements.
 *
 * Restore policy:
 *   - DELETE FROM <table> WHERE 1=1 before re-inserting (clean slate per table).
 *     Caller is responsible for FSM rewind / cache flush around this call.
 *
 * @package WP_Data_Optimizer
 */

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

/**
 * Snapshot reader: integrity check + apply.
 */
class TMDO_Snapshot_Reader {

	/**
	 * Catalog row from wp_wpdo_snapshots.
	 *
	 * @var array<string,mixed>
	 */
	private array $row;

	/**
	 * Constructor.
	 *
	 * @param array $row Catalog row (must contain snapshot_id, storage, file_path, file_sha256, inline_blob, size_bytes).
	 * @throws InvalidArgumentException When row is missing required keys.
	 */
	public function __construct( array $row ) {
		foreach ( array( 'snapshot_id', 'storage', 'size_bytes' ) as $required ) {
			if ( ! array_key_exists( $required, $row ) ) {
				throw new InvalidArgumentException( "snapshot row missing key: {$required}" ); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- exception message, not HTML output
			}
		}
		$this->row = $row;
	}

	/**
	 * Verify sha256 + readability.
	 *
	 * @return array {ok:bool, sha256_ok:bool, size_match:bool, error?:string}
	 */
	public function verify(): array {
		$storage       = (string) $this->row['storage'];
		$expected_size = (int) $this->row['size_bytes'];
		$expected_sha  = (string) ( $this->row['file_sha256'] ?? '' );

		if ( 'inline' === $storage ) {
			$blob        = (string) ( $this->row['inline_blob'] ?? '' );
			$actual_size = strlen( $blob );
			// inline blobs aren't sha-checked by default — just check size.
			return array(
				'ok'         => $actual_size === $expected_size,
				'sha256_ok'  => true,
				'size_match' => $actual_size === $expected_size,
				'storage'    => 'inline',
			);
		}

		$path = (string) ( $this->row['file_path'] ?? '' );
		if ( '' === $path || ! file_exists( $path ) ) {
			return array(
				'ok'      => false,
				'error'   => 'file_missing',
				'storage' => 'file',
			);
		}
		if ( ! is_readable( $path ) ) {
			return array(
				'ok'      => false,
				'error'   => 'file_unreadable',
				'storage' => 'file',
			);
		}
		$actual_size = (int) filesize( $path );
		$actual_sha  = hash_file( 'sha256', $path );
		return array(
			'ok'         => ( $actual_size === $expected_size ) && ( $actual_sha === $expected_sha ),
			'sha256_ok'  => ( $actual_sha === $expected_sha ),
			'size_match' => ( $actual_size === $expected_size ),
			'storage'    => 'file',
		);
	}

	/**
	 * Parse SQL stream and return a preview of tables + row counts (no apply).
	 *
	 * @return array {tables:array<string,int>, total_rows:int, statements:int, sql_bytes:int}
	 * @throws RuntimeException When payload cannot be loaded.
	 */
	public function preview(): array {
		$sql = $this->load_sql();
		return $this->parse_summary( $sql );
	}

	/**
	 * Load + apply (DELETE + INSERT per table).
	 *
	 * For file-storage snapshots, sha256 is verified before execution.
	 * Only tables whose names pass is_safe_name() (prefix-prefixed, alphanum+_)
	 * are touched — arbitrary table names in the SQL file cannot be applied.
	 *
	 * @return array {tables:array<int,string>, rows_restored:int, statements_run:int}
	 * @throws RuntimeException When payload cannot be loaded or integrity check fails.
	 */
	public function apply(): array {
		global $wpdb;

		// Verify sha256 / size for file-storage snapshots before executing any SQL.
		if ( 'inline' !== (string) ( $this->row['storage'] ?? 'file' ) ) {
			$check = $this->verify();
			if ( ! $check['ok'] ) {
				$reason = $check['error'] ?? ( $check['sha256_ok'] ? 'size_mismatch' : 'sha256_mismatch' );
				throw new RuntimeException( 'snapshot integrity check failed: ' . $reason ); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- exception message, not HTML output
			}
		}

		$sql     = $this->load_sql();
		$summary = $this->parse_summary( $sql );

		// Wipe target tables before inserting (clean slate).
		foreach ( array_keys( $summary['tables'] ) as $table ) {
			if ( $this->is_safe_name( $table ) ) {
				$wpdb->query( "DELETE FROM `{$table}`" ); // phpcs:ignore WordPress.DB
			}
		}

		$statements_run = 0;
		$rows_restored  = 0;
		// Naive split on `;\n` — INSERT statements never contain unescaped semicolon-newline.
		$lines = preg_split( '/;\s*\n/', $sql );
		if ( ! is_array( $lines ) ) {
			throw new RuntimeException( 'sql parse failed' );
		}
		foreach ( $lines as $stmt ) {
			$stmt = trim( $stmt );
			if ( '' === $stmt || str_starts_with( $stmt, '--' ) ) {
				continue;
			}
			if ( ! preg_match( '/^(INSERT|SET)\b/i', $stmt ) ) {
				continue;
			}
			$result = $wpdb->query( $stmt ); // phpcs:ignore WordPress.DB
			if ( false === $result ) {
				throw new RuntimeException( 'restore stmt failed: ' . substr( $stmt, 0, 80 ) ); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- exception message, not HTML output
			}
			if ( stripos( $stmt, 'INSERT' ) === 0 ) {
				$rows_restored += (int) $result;
			}
			++$statements_run;
		}

		return array(
			'tables'         => array_keys( $summary['tables'] ),
			'rows_restored'  => $rows_restored,
			'statements_run' => $statements_run,
		);
	}

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

	/**
	 * Load + ungzip the snapshot SQL payload.
	 *
	 * @return string Raw SQL.
	 * @throws RuntimeException When payload is missing or unreadable.
	 */
	private function load_sql(): string {
		$storage = (string) $this->row['storage'];
		if ( 'inline' === $storage ) {
			$blob = (string) ( $this->row['inline_blob'] ?? '' );
			if ( '' === $blob ) {
				throw new RuntimeException( 'inline_blob is empty' );
			}
			return $this->maybe_gunzip( $blob );
		}
		$path = (string) ( $this->row['file_path'] ?? '' );
		if ( '' === $path || ! file_exists( $path ) ) {
			throw new RuntimeException( 'snapshot file missing: ' . $path ); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- exception message, not HTML output
		}
		if ( str_ends_with( $path, '.gz' ) ) {
			$content = '';
			$handle  = gzopen( $path, 'rb' );
			if ( false === $handle ) {
				throw new RuntimeException( 'gzopen failed: ' . $path ); // phpcs:ignore WordPress.Security.EscapeOutput.ExceptionNotEscaped -- exception message, not HTML output
			}
			while ( ! gzeof( $handle ) ) {
				$content .= gzread( $handle, 65536 );
			}
			gzclose( $handle );
			return $content;
		}
		return (string) file_get_contents( $path );
	}

	/**
	 * Decompress if first 2 bytes are gzip magic.
	 *
	 * @param string $blob Possibly-gzipped data.
	 * @return string Decompressed.
	 */
	private function maybe_gunzip( string $blob ): string {
		if ( strlen( $blob ) >= 2 && "\x1f\x8b" === substr( $blob, 0, 2 ) ) {
			$out = @gzdecode( $blob ); // phpcs:ignore WordPress.PHP.NoSilencedErrors
			return false === $out ? $blob : $out;
		}
		return $blob;
	}

	/**
	 * Walk SQL and count INSERT rows per table.
	 *
	 * @param string $sql Raw SQL.
	 * @return array {tables:array<string,int>, total_rows:int, statements:int, sql_bytes:int}
	 */
	private function parse_summary( string $sql ): array {
		$tables     = array();
		$total      = 0;
		$statements = 0;
		preg_match_all( '/INSERT INTO `([^`]+)` \([^)]*\) VALUES (.+?);\s*\n/s', $sql, $matches, PREG_SET_ORDER );
		foreach ( $matches as $m ) {
			$table = $m[1];
			$body  = $m[2];
			// Count `(` at the start of value tuples — substring_count of `,(` + 1.
			$rows             = substr_count( $body, "),\n  (" ) + 1;
			$tables[ $table ] = ( $tables[ $table ] ?? 0 ) + $rows;
			$total           += $rows;
			++$statements;
		}
		return array(
			'tables'     => $tables,
			'total_rows' => $total,
			'statements' => $statements,
			'sql_bytes'  => strlen( $sql ),
		);
	}

	/**
	 * Match safe table names: alphanumeric + underscore, must start with $wpdb->prefix.
	 *
	 * Mirrors TMDO_Snapshot_Writer::is_safe_name() so writer and reader apply
	 * the same gate — an attacker-crafted SQL file cannot target tables outside
	 * this site's WordPress 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;
	}
}