<?php
/**
 * The .shiftbox archive format.
 *
 * A flat, append-only stream that can be written and read in many short requests:
 *
 *   MAGIC (10 bytes)
 *   repeat: "SBF" | uint16 path length | uint32 size-high | uint32 size-low | uint32 mtime | path | content
 *   "SBE"
 *
 * No compression: media is already compressed, and skipping it keeps
 * exports and imports fast on shared hosting.
 *
 * @package Shiftbox
 */

// phpcs:disable WordPress.WP.AlternativeFunctions

defined( 'ABSPATH' ) || exit;

/**
 * Archive helpers.
 */
class Shiftbox_Archive {

	const MAGIC      = "SHIFTBOX\x01\n";
	const ENTRY      = 'SBF';
	const END        = 'SBE';
	const HEADER_LEN = 17;

	/**
	 * Builds an entry header.
	 *
	 * @param string $path  Path inside the archive.
	 * @param int    $size  Content size.
	 * @param int    $mtime Modified time.
	 * @return string
	 */
	public static function entry_header( $path, $size, $mtime ) {
		$size = (int) $size;
		return self::ENTRY
			. pack( 'n', strlen( $path ) )
			. pack( 'N', ( $size >> 32 ) & 0xFFFFFFFF )
			. pack( 'N', $size & 0xFFFFFFFF )
			. pack( 'N', max( 0, (int) $mtime ) & 0xFFFFFFFF )
			. $path;
	}

	/**
	 * Reads the next entry header at the current position.
	 *
	 * @param resource $fh Handle.
	 * @return array|null Entry (path, size, mtime, data_offset) or null at end.
	 * @throws RuntimeException When the archive is damaged.
	 */
	public static function read_header( $fh ) {
		$tag = fread( $fh, 3 );
		if ( self::END === $tag ) {
			return null;
		}
		if ( self::ENTRY !== $tag ) {
			throw new RuntimeException( esc_html( __( 'The backup file is damaged or incomplete. Upload it again or pick another backup.', 'shiftbox' ) ) );
		}
		$raw = fread( $fh, 14 );
		if ( strlen( $raw ) !== 14 ) {
			throw new RuntimeException( esc_html( __( 'The backup file ends early. It was probably not fully uploaded.', 'shiftbox' ) ) );
		}
		$h    = unpack( 'nlen/Nhi/Nlo/Nmtime', $raw );
		$path = $h['len'] > 0 ? fread( $fh, $h['len'] ) : '';
		if ( strlen( $path ) !== $h['len'] ) {
			throw new RuntimeException( esc_html( __( 'The backup file ends early. It was probably not fully uploaded.', 'shiftbox' ) ) );
		}
		return array(
			'path'        => $path,
			'size'        => ( $h['hi'] * 4294967296 ) + $h['lo'],
			'mtime'       => $h['mtime'],
			'data_offset' => ftell( $fh ),
		);
	}

	/**
	 * Checks the magic header.
	 *
	 * @param string $file Archive path.
	 * @return bool
	 */
	public static function is_archive( $file ) {
		$fh = @fopen( $file, 'rb' ); // phpcs:ignore WordPress.PHP.NoSilencedErrors.Discouraged
		if ( ! $fh ) {
			return false;
		}
		$magic = fread( $fh, strlen( self::MAGIC ) );
		fclose( $fh );
		return self::MAGIC === $magic;
	}

	/**
	 * Reads package.json, which is always the first entry.
	 *
	 * @param string $file Archive path.
	 * @return array|WP_Error
	 */
	public static function read_manifest( $file ) {
		if ( ! self::is_archive( $file ) ) {
			return new WP_Error( 'shiftbox_not_archive', __( 'This is not a Shiftbox backup file (.shiftbox).', 'shiftbox' ) );
		}
		$fh = fopen( $file, 'rb' );
		fseek( $fh, strlen( self::MAGIC ) );
		try {
			$entry = self::read_header( $fh );
		} catch ( RuntimeException $e ) {
			fclose( $fh );
			return new WP_Error( 'shiftbox_damaged', $e->getMessage() );
		}
		if ( ! $entry || 'package.json' !== $entry['path'] || $entry['size'] > 1048576 ) {
			fclose( $fh );
			return new WP_Error( 'shiftbox_damaged', __( 'The backup file has no package information.', 'shiftbox' ) );
		}
		$json = $entry['size'] > 0 ? fread( $fh, $entry['size'] ) : '';
		fclose( $fh );
		$data = json_decode( $json, true );
		if ( ! is_array( $data ) ) {
			return new WP_Error( 'shiftbox_damaged', __( 'The backup package information could not be read.', 'shiftbox' ) );
		}
		return $data;
	}

	/**
	 * Validates a path read from an archive. Returns a clean relative path or false.
	 *
	 * @param string $path Path.
	 * @return string|false
	 */
	public static function clean_path( $path ) {
		if ( '' === $path || false !== strpos( $path, "\0" ) || false !== strpos( $path, '\\' ) ) {
			return false;
		}
		if ( '/' === $path[0] || preg_match( '/^[A-Za-z]:/', $path ) ) {
			return false;
		}
		foreach ( explode( '/', $path ) as $part ) {
			if ( '' === $part || '.' === $part || '..' === $part ) {
				return false;
			}
		}
		return $path;
	}
}