angular/devtools/projects/ng-devtools-backend/src/lib/highlighter.ts

let overlay: any;
let overlayContent: HTMLElement;

declare const ng: any;

interface Type<T> extends Function {
  new (...args: any[]): T;
}

export const DEV_TOOLS_HIGHLIGHT_NODE_ID = '____ngDevToolsHighlight';

function init(): void {
  if (overlay) {
    return;
  }
  overlay = document.createElement('div');
  overlay.style.backgroundColor = 'rgba(104, 182, 255, 0.35)';
  overlay.style.position = 'fixed';
  overlay.style.zIndex = '2147483647';
  overlay.style.pointerEvents = 'none';
  overlay.style.display = 'flex';
  overlay.style.borderRadius = '3px';
  overlay.setAttribute('id', DEV_TOOLS_HIGHLIGHT_NODE_ID);
  overlayContent = document.createElement('div');
  overlayContent.style.backgroundColor = 'rgba(104, 182, 255, 0.9)';
  overlayContent.style.position = 'absolute';
  overlayContent.style.bottom = '-23px';
  overlayContent.style.right = '0px';
  overlayContent.style.fontFamily = 'monospace';
  overlayContent.style.fontSize = '11px';
  overlayContent.style.padding = '2px 3px';
  overlayContent.style.borderRadius = '3px';
  overlayContent.style.color = 'white';
  overlay.appendChild(overlayContent);
}

export const findComponentAndHost = (el: Node | undefined): { component: any; host: HTMLElement | null } => {
  if (!el) {
    return { component: null, host: null };
  }
  while (el) {
    const component = el instanceof HTMLElement && ng.getComponent(el);
    if (component) {
      return { component, host: el as HTMLElement };
    }
    if (!el.parentElement) {
      break;
    }
    el = el.parentElement;
  }
  return { component: null, host: null };
};

// Todo(aleksanderbodurri): this should not be part of the highlighter, move this somewhere else
export const getDirectiveName = (dir: Type<unknown> | undefined | null): string => {
  if (dir) {
    return dir.constructor.name;
  }
  return 'unknown';
};

export const highlight = (el: HTMLElement): void => {
  const cmp = findComponentAndHost(el).component;
  const rect = getComponentRect(el);

  init();
  if (rect) {
    const content: Node[] = [];
    const name = getDirectiveName(cmp);
    if (name) {
      const pre = document.createElement('span');
      pre.style.opacity = '0.6';
      pre.innerText = '<';
      const text = document.createTextNode(name);
      const post = document.createElement('span');
      post.style.opacity = '0.6';
      post.innerText = '>';
      content.push(pre, text, post);
    }
    showOverlay(rect, content);
  }
};

export function unHighlight(): void {
  if (overlay && overlay.parentNode) {
    document.body.removeChild(overlay);
  }
}

export function inDoc(node: any): boolean {
  if (!node) {
    return false;
  }
  const doc = node.ownerDocument.documentElement;
  const parent = node.parentNode;
  return doc === node || doc === parent || !!(parent && parent.nodeType === 1 && doc.contains(parent));
}

export function getComponentRect(el: Node): DOMRect | ClientRect | undefined {
  if (!(el instanceof HTMLElement)) {
    return;
  }
  if (!inDoc(el)) {
    return;
  }
  return el.getBoundingClientRect();
}

interface OverlayDimensionsAndPosition {
  width: number;
  height: number;
  top: number;
  left: number;
}

function showOverlay(
  { width = 0, height = 0, top = 0, left = 0 }: OverlayDimensionsAndPosition,
  content: any[] = []
): void {
  overlay.style.width = ~~width + 'px';
  overlay.style.height = ~~height + 'px';
  overlay.style.top = ~~top + 'px';
  overlay.style.left = ~~left + 'px';

  while (overlayContent.children.length) {
    const { children } = overlayContent;
    overlayContent.removeChild(children[children.length - 1]);
  }

  content.forEach((child) => overlayContent.appendChild(child));

  document.body.appendChild(overlay);
}