<?php
// Общий inline-контракт Back для незавершённой публичной операции (api#299/preland#9).
return <<<'JS'
(() => {
	let active = false;
	let hasHistoryEntry = false;
	let releasingHistoryEntry = false;
	let returningToSentinel = false;

	function pushGuardEntries() {
		// Помечаем и текущую запись Tour, и sentinel сверху. Иначе первый Back
		// останавливался на немаркированной записи, а второй мог уйти в about:blank.
		window.history.replaceState({ publicOperationGuard: true }, '', window.location.href);
		window.history.pushState({ publicOperationGuard: true }, '', window.location.href);
		hasHistoryEntry = true;
	}

	function onPopState(event) {
		if (releasingHistoryEntry) {
			releasingHistoryEntry = false;
			return;
		}

		if (active) {
			if (returningToSentinel) {
				returningToSentinel = false;
				return;
			}
			returningToSentinel = true;
			window.history.go(1);
		}
	}

	function deactivate(onReleased) {
		if (!active) {
			if (onReleased) {
				if (releasingHistoryEntry) {
					window.addEventListener('popstate', onReleased, { once: true });
				} else {
					onReleased();
				}
			}
			return;
		}
		active = false;

		if (hasHistoryEntry) {
			hasHistoryEntry = false;
			releasingHistoryEntry = true;
			if (onReleased) window.addEventListener('popstate', onReleased, { once: true });
			window.history.back();
			return;
		}
		if (onReleased) onReleased();
	}

	window.addEventListener('popstate', onPopState);
	window.PublicNavigationGuard = {
		activate() {
			if (active) return;
			releasingHistoryEntry = false;
			returningToSentinel = false;
			active = true;
			pushGuardEntries();
		},
		deactivate,
		allowNavigation: deactivate,
	};
})();
JS;