<?php
/**
 * One scan under way.
 *
 * @package WorkMoreCookieCrumb
 */

namespace WorkMore\CookieCrumb\Scan;

/**
 * A scan is many requests — the pages opened in the owner's browser, and
 * what the browser reports of each — tied together by a token. What each
 * request saw is kept as a note of its own (two frames load at the same
 * time: one note for all of them would lose what the slower one wrote),
 * for a few minutes, until the scan is read out and put away.
 */
final class Session {

	/**
	 * Seconds a scan has to finish.
	 */
	private const KEEP = 1200;

	/**
	 * The parts of a page a note can be about: what the server sent, what
	 * the browser saw with everything allowed, and what it saw as a visitor
	 * who has not answered.
	 */
	public const PARTS = array( 'server', 'inventory', 'check' );

	/**
	 * Start a scan.
	 *
	 * @param int                $user_id Who scans.
	 * @param array<int, string> $pages   The pages, in order.
	 * @return string The scan's token.
	 */
	public static function start( int $user_id, array $pages ): string {
		$token = strtolower( wp_generate_password( 20, false ) );

		set_transient(
			self::key( $token ),
			array(
				'user'  => $user_id,
				'pages' => array_values( $pages ),
				'time'  => time(),
			),
			self::KEEP
		);

		return $token;
	}

	/**
	 * A scan under way (null: there is none by that token).
	 *
	 * @param string $token Token.
	 * @return array{user: int, pages: array<int, string>, time: int}|null
	 */
	public static function get( string $token ): ?array {
		if ( 1 !== preg_match( '/^[a-z0-9]{20}$/', $token ) ) {
			return null;
		}

		$scan = get_transient( self::key( $token ) );

		if ( ! is_array( $scan ) || ! isset( $scan['user'], $scan['pages'] ) || ! is_array( $scan['pages'] ) ) {
			return null;
		}

		return array(
			'user'  => (int) $scan['user'],
			'pages' => array_values( array_filter( $scan['pages'], 'is_string' ) ),
			'time'  => (int) ( $scan['time'] ?? 0 ),
		);
	}

	/**
	 * Keep what one request saw of one page.
	 *
	 * @param string               $token Token.
	 * @param int                  $index The page's place in the scan.
	 * @param string               $part  One of PARTS.
	 * @param array<string, mixed> $seen  What was seen.
	 * @return void
	 */
	public static function note( string $token, int $index, string $part, array $seen ): void {
		$scan = self::get( $token );

		if ( null !== $scan && isset( $scan['pages'][ $index ] ) && in_array( $part, self::PARTS, true ) ) {
			set_transient( self::key( $token, $index, $part ), $seen, self::KEEP );
		}
	}

	/**
	 * Everything the scan's requests saw, page by page.
	 *
	 * @param string $token Token.
	 * @return array<int, array{url: string, server: array<string, mixed>|null, inventory: array<string, mixed>|null, check: array<string, mixed>|null}>
	 */
	public static function read( string $token ): array {
		$scan  = self::get( $token );
		$pages = array();

		foreach ( null === $scan ? array() : $scan['pages'] as $index => $url ) {
			$page = array( 'url' => $url );

			foreach ( self::PARTS as $part ) {
				$seen          = get_transient( self::key( $token, $index, $part ) );
				$page[ $part ] = is_array( $seen ) ? $seen : null;
			}

			$pages[] = $page;
		}

		return $pages;
	}

	/**
	 * Put a scan away: its notes are no longer needed.
	 *
	 * @param string $token Token.
	 * @return void
	 */
	public static function end( string $token ): void {
		$scan = self::get( $token );

		foreach ( null === $scan ? array() : array_keys( $scan['pages'] ) as $index ) {
			foreach ( self::PARTS as $part ) {
				delete_transient( self::key( $token, $index, $part ) );
			}
		}

		delete_transient( self::key( $token ) );
	}

	/**
	 * The name a scan, or one of its notes, is kept under.
	 *
	 * @param string   $token Token.
	 * @param int|null $index A page's place (null: the scan itself).
	 * @param string   $part  One of PARTS.
	 * @return string
	 */
	private static function key( string $token, ?int $index = null, string $part = '' ): string {
		return 'wmcc_scan_' . $token . ( null === $index ? '' : '_' . $index . '_' . $part );
	}
}