import {dom, IDomArgs, Observable, styled} from 'grainjs'; // Shadow css settings for member scroll top and bottom. const SHADOW_TOP = 'inset 0 4px 6px 0 rgba(217,217,217,0.4)'; const SHADOW_BTM = 'inset 0 -4px 6px 0 rgba(217,217,217,0.4)'; /** * Creates a scroll div used in the UserManager and moveDoc menus to display * shadows at the top and bottom of a list of scrollable items. */ export function shadowScroll(...args: IDomArgs) { // Observables to indicate the scroll position. const scrollTop = Observable.create(null, true); const scrollBtm = Observable.create(null, true); return cssScrollMenu( dom.autoDispose(scrollTop), dom.autoDispose(scrollBtm), // Update scroll positions on init and on scroll. (elem) => { setTimeout(() => scrollBtm.set(isAtScrollBtm(elem)), 0); }, dom.on('scroll', (_, elem) => { scrollTop.set(isAtScrollTop(elem)); scrollBtm.set(isAtScrollBtm(elem)); }), // Add shadows on the top/bottom if the list is scrolled away from either. dom.style('box-shadow', (use) => { const shadows = [use(scrollTop) ? null : SHADOW_TOP, use(scrollBtm) ? null : SHADOW_BTM]; return shadows.filter(css => css).join(', '); }), ...args ); } // Indicates that an element is currently scrolled such that the top of the element is visible. function isAtScrollTop(elem: Element): boolean { return elem.scrollTop === 0; } // Indicates that an element is currently scrolled such that the bottom of the element is visible. // It is expected that the elem arg has the offsetHeight property set. function isAtScrollBtm(elem: HTMLElement): boolean { return elem.scrollTop >= (elem.scrollHeight - elem.offsetHeight); } const cssScrollMenu = styled('div', ` flex: 1 1 0; width: 100%; overflow-y: auto; `);