<?php
/**
 * The Accessible Forms export file.
 *
 * Version 2 holds several forms with their name, key and optional reviewed
 * recipients, plus optional settings. Version 1 files (one form, made by Pro 1.x)
 * are read as version 2. A checksum catches truncated or hand-edited files.
 *
 * @package AccessibleForms
 */

namespace AccessibleForms\Portability;

use AccessibleForms\Schema;

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

class Package {
	const FORMAT    = 'accessible-forms';
	const VERSION   = 2;
	const MAX_BYTES = 1048576;
	const MAX_FORMS = 100;
	const MAX_DEPTH = 40;

	/**
	 * A complete file from its parts.
	 *
	 * @param array $forms    Exported forms (see FormTransfer::export()).
	 * @param array $settings Portable settings, or an empty array.
	 * @param array $extra    Further top-level sections added by add-ons, keyed by name.
	 * @return array
	 */
	public static function build( array $forms, array $settings = array(), array $extra = array() ) {
		$package = array(
			'format'     => self::FORMAT,
			'version'    => self::VERSION,
			'generator'  => (array) \AccessibleForms\Extensions::filter(
				'accessible_forms_export_generator',
				array(
					'free'          => \AccessibleForms\VERSION,
					'extension_api' => \AccessibleForms\API_VERSION,
				)
			),
			'created_at' => gmdate( 'Y-m-d\TH:i:s\Z' ),
			'contains'   => array_values(
				array_merge(
					$forms ? array( 'forms' ) : array(),
					$settings ? array( 'settings' ) : array(),
					array_keys( $extra )
				)
			),
			'forms'      => array_values( $forms ),
		);
		if ( $settings ) {
			$package['settings'] = $settings;
		}
		foreach ( $extra as $name => $section ) {
			if ( ! isset( $package[ $name ] ) ) {
				$package[ $name ] = $section;
			}
		}
		$package['checksum'] = self::checksum( $package );
		return $package;
	}

	/** Pretty, readable JSON. */
	public static function encode( array $package ) {
		return (string) wp_json_encode( $package, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES );
	}

	/** Refuse a download that this importer cannot read, without truncating anything. */
	public static function download( array $package ) {
		$json = self::encode( $package );
		$decoded = self::decode( $json );
		return is_wp_error( $decoded ) ? $decoded : $json;
	}

	/**
	 * Read a file. Values are left unsanitized here; the importer sanitizes every
	 * form through Schema::sanitize() and every setting through the settings rules.
	 *
	 * @param mixed $json File contents.
	 * @return array|\WP_Error Package with `checksum_ok` and `source_version` added.
	 */
	public static function decode( $json ) {
		if ( ! is_string( $json ) || '' === trim( $json ) ) {
			return new \WP_Error( 'empty', __( 'Choose an Accessible Forms export file.', 'accessible-forms-by-accessible-org' ) );
		}
		if ( strlen( $json ) > self::MAX_BYTES ) {
			return new \WP_Error( 'size', __( 'This file is larger than 1 MB. Export fewer forms at a time.', 'accessible-forms-by-accessible-org' ) );
		}
		// A UTF-8 byte order mark from some editors is not part of the JSON.
		$json = preg_replace( '/^\xEF\xBB\xBF/', '', $json );
		$data = json_decode( $json, true, self::MAX_DEPTH );
		if ( ! is_array( $data ) ) {
			return new \WP_Error( 'json', __( 'This file is not valid JSON. Export it again, without editing it.', 'accessible-forms-by-accessible-org' ) );
		}
		// The checksum covers the file as written, before values are cleaned.
		$checksum_ok = is_string( $data['checksum'] ?? null ) && hash_equals( self::checksum( $data ), $data['checksum'] );
		$data        = Schema::clean_input( $data );
		if ( self::FORMAT !== ( $data['format'] ?? '' ) ) {
			return new \WP_Error( 'format', __( 'This is not an Accessible Forms export file.', 'accessible-forms-by-accessible-org' ) );
		}
		$version = $data['version'] ?? 0;
		if ( 1 === $version ) {
			return self::from_version_1( $data );
		}
		if ( ! is_int( $version ) || $version < 1 ) {
			return new \WP_Error( 'format', __( 'This is not a supported Accessible Forms export.', 'accessible-forms-by-accessible-org' ) );
		}
		if ( $version > self::VERSION ) {
			return new \WP_Error( 'newer', __( 'This file was made by a newer version of Accessible Forms. Update the plugin on this site, then import it.', 'accessible-forms-by-accessible-org' ) );
		}
		$forms = $data['forms'] ?? array();
		if ( ! is_array( $forms ) || ! array_is_list( $forms ) ) {
			return new \WP_Error( 'format', __( 'The forms in this file are not readable.', 'accessible-forms-by-accessible-org' ) );
		}
		if ( count( $forms ) > self::MAX_FORMS ) {
			return new \WP_Error( 'count', __( 'This file has more than 100 forms. Export fewer forms at a time.', 'accessible-forms-by-accessible-org' ) );
		}
		foreach ( $forms as $form ) {
			if ( ! is_array( $form ) || ! is_array( $form['schema'] ?? null ) ) {
				return new \WP_Error( 'format', __( 'A form in this file is not readable.', 'accessible-forms-by-accessible-org' ) );
			}
		}
		if ( isset( $data['settings'] ) && ! is_array( $data['settings'] ) ) {
			unset( $data['settings'] );
		}
		$data['checksum_ok']    = $checksum_ok;
		$data['source_version'] = $version;
		return $data;
	}

	/**
	 * SHA-256 of the file's content in a canonical order, without the checksum
	 * itself and the values added when reading.
	 */
	public static function checksum( array $package ) {
		unset( $package['checksum'], $package['checksum_ok'], $package['source_version'] );
		return hash( 'sha256', (string) wp_json_encode( self::canonical( $package ), JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES ) );
	}

	private static function canonical( $value ) {
		if ( ! is_array( $value ) ) {
			return $value;
		}
		if ( ! array_is_list( $value ) ) {
			ksort( $value, SORT_STRING );
		}
		return array_map( array( self::class, 'canonical' ), $value );
	}

	/** A Pro 1.x file holds one form's configuration and nothing else. */
	private static function from_version_1( array $data ) {
		if ( ! is_array( $data['schema'] ?? null ) ) {
			return new \WP_Error( 'format', __( 'This is not a supported Accessible Forms export.', 'accessible-forms-by-accessible-org' ) );
		}
		$heading = is_string( $data['schema']['heading'] ?? null ) ? $data['schema']['heading'] : '';
		return array(
			'format'         => self::FORMAT,
			'version'        => self::VERSION,
			'contains'       => array( 'forms' ),
			'forms'          => array(
				array(
					'key'    => '',
					'title'  => $heading,
					'schema' => $data['schema'],
				),
			),
			// Version 1 had no checksum; there is nothing to compare.
			'checksum_ok'    => true,
			'source_version' => 1,
		);
	}
}