1 files changed, 134 insertions, 0 deletions
diff --git a/src/content/presenters/FollowPresenter.ts b/src/content/presenters/FollowPresenter.ts
new file mode 100644
index 0000000..f0d115c
--- /dev/null
+++ b/src/content/presenters/FollowPresenter.ts
@@ -0,0 +1,134 @@
+import Hint, { InputHint, LinkHint } from './Hint';
+import * as doms from '../../shared/utils/dom';
+
+const TARGET_SELECTOR = [
+  'a', 'button', 'input', 'textarea', 'area',
+  '[contenteditable=true]', '[contenteditable=""]', '[tabindex]',
+  '[role="button"]', 'summary'
+].join(',');
+
+interface Size {
+  width: number;
+  height: number;
+}
+
+interface Point {
+  x: number;
+  y: number;
+}
+
+const inViewport = (
+  win: Window,
+  element: Element,
+  viewSize: Size,
+  framePosition: Point,
+): boolean => {
+  let {
+    top, left, bottom, right
+  } = doms.viewportRect(element);
+  let doc = win.document;
+  let frameWidth = doc.documentElement.clientWidth;
+  let frameHeight = doc.documentElement.clientHeight;
+
+  if (right < 0 || bottom < 0 || top > frameHeight || left > frameWidth) {
+    // out of frame
+    return false;
+  }
+  if (right + framePosition.x < 0 || bottom + framePosition.y < 0 ||
+      left + framePosition.x > viewSize.width ||
+      top + framePosition.y > viewSize.height) {
+    // out of viewport
+    return false;
+  }
+  return true;
+};
+
+const isAriaHiddenOrAriaDisabled = (win: Window, element: Element): boolean => {
+  if (!element || win.document.documentElement === element) {
+    return false;
+  }
+  for (let attr of ['aria-hidden', 'aria-disabled']) {
+    let value = element.getAttribute(attr);
+    if (value !== null) {
+      let hidden = value.toLowerCase();
+      if (hidden === '' || hidden === 'true') {
+        return true;
+      }
+    }
+  }
+  return isAriaHiddenOrAriaDisabled(win, element.parentElement as Element);
+};
+
+export default interface FollowPresenter {
+  getTargetCount(viewSize: Size, framePosition: Point): number;
+
+  createHints(viewSize: Size, framePosition: Point, tags: string[]): void;
+
+  filterHints(prefix: string): void;
+
+  clearHints(): void;
+
+  getHint(tag: string): Hint | undefined;
+
+  // eslint-disable-next-line semi
+}
+
+export class FollowPresenterImpl implements FollowPresenter {
+  private hints: Hint[]
+
+  constructor() {
+    this.hints = [];
+  }
+
+  getTargetCount(viewSize: Size, framePosition: Point): number {
+    let targets = this.getTargets(viewSize, framePosition);
+    return targets.length;
+  }
+
+  createHints(viewSize: Size, framePosition: Point, tags: string[]): void {
+    let targets = this.getTargets(viewSize, framePosition);
+    let min = Math.min(targets.length, tags.length);
+    for (let i = 0; i < min; ++i) {
+      let target = targets[i];
+      if (target instanceof HTMLAnchorElement ||
+        target instanceof HTMLAreaElement) {
+        this.hints.push(new LinkHint(target, tags[i]));
+      } else {
+        this.hints.push(new InputHint(target, tags[i]));
+      }
+    }
+  }
+
+  filterHints(prefix: string): void {
+    let shown = this.hints.filter(h => h.getTag().startsWith(prefix));
+    let hidden = this.hints.filter(h => !h.getTag().startsWith(prefix));
+
+    shown.forEach(h => h.show());
+    hidden.forEach(h => h.hide());
+  }
+
+  clearHints(): void {
+    this.hints.forEach(h => h.remove());
+    this.hints = [];
+  }
+
+  getHint(tag: string): Hint | undefined {
+    return this.hints.find(h => h.getTag() === tag);
+  }
+
+  private getTargets(viewSize: Size, framePosition: Point): HTMLElement[] {
+    let all = window.document.querySelectorAll(TARGET_SELECTOR);
+    let filtered = Array.prototype.filter.call(all, (element: HTMLElement) => {
+      let style = window.getComputedStyle(element);
+
+      // AREA's 'display' in Browser style is 'none'
+      return (element.tagName === 'AREA' || style.display !== 'none') &&
+        style.visibility !== 'hidden' &&
+        (element as HTMLInputElement).type !== 'hidden' &&
+        element.offsetHeight > 0 &&
+        !isAriaHiddenOrAriaDisabled(window, element) &&
+        inViewport(window, element, viewSize, framePosition);
+    });
+    return filtered;
+  }
+}