// Full-viewport Overlay component (mobile). Distinct from the .modal dialog:
// this hosts a whole sidebar at full screen with its own scroll and a top-right close control.
// It reuses the low-level focus/Escape/bfcache patterns from modal.js rather than that component's panel chrome.
//
// openOverlay(node) MOVES `node` (an existing rail <aside>) into the overlay
// body and restores it to its original DOM position on close, so the rail keeps
// its state (expanded tree folders, rendered TOC). Only one overlay is open at
// a time.
(function () {
    var overlay = null;
    var bodyEl = null;
    var closeBtn = null;
    var hosted = null;      // the moved node
    var placeholder = null; // marks where to restore it
    var prevFocus = null;
    var onKeydown = null;

    function build() {
        overlay = document.createElement('div');
        overlay.className = 'overlay';
        overlay.setAttribute('role', 'dialog');
        overlay.setAttribute('aria-modal', 'true');

        var bar = document.createElement('div');
        bar.className = 'overlay-bar';

        closeBtn = document.createElement('button');
        closeBtn.type = 'button';
        closeBtn.className = 'btn overlay-close';
        closeBtn.title = 'Close';
        closeBtn.setAttribute('aria-label', 'Close');
        closeBtn.textContent = '×';
        closeBtn.addEventListener('click', close);
        bar.appendChild(closeBtn);

        bodyEl = document.createElement('div');
        bodyEl.className = 'overlay-body';
        bodyEl.addEventListener('click', function (e) {
            if (e.target.closest('a')) close();
        });

        overlay.appendChild(bar);
        overlay.appendChild(bodyEl);
    }

    function open(node) {
        if (overlay && overlay.parentNode) close();
        if (!overlay) build();

        prevFocus = document.activeElement;
        hosted = node;
        placeholder = document.createComment('overlay-slot');
        node.parentNode.insertBefore(placeholder, node);
        bodyEl.appendChild(node);

        document.body.appendChild(overlay);
        overlay.classList.add('is-open');

        onKeydown = function (e) {
            if (e.key === 'Escape') { e.preventDefault(); close(); }
        };
        document.addEventListener('keydown', onKeydown);

        setTimeout(function () { closeBtn.focus(); }, 0);
    }

    function close() {
        if (!overlay || !overlay.parentNode) return;
        if (onKeydown) {
            document.removeEventListener('keydown', onKeydown);
            onKeydown = null;
        }
        // Restore the hosted rail to its original spot in the shell.
        if (hosted && placeholder && placeholder.parentNode) {
            placeholder.parentNode.insertBefore(hosted, placeholder);
            placeholder.parentNode.removeChild(placeholder);
        }
        hosted = null;
        placeholder = null;
        overlay.classList.remove('is-open');
        overlay.parentNode.removeChild(overlay);

        var toRestore = prevFocus;
        prevFocus = null;
        if (toRestore && toRestore.focus) {
            try { toRestore.focus(); } catch (e) {}
        }
    }

    // Belt-and-suspenders bfcache guard: force the overlay closed (restoring
    // the rail) if the page is being hidden while it is still open.
    window.addEventListener('pagehide', close);

    window.openOverlay = open;
    window.closeOverlay = close;
})();