From 4c551386b100ea4b694c1e8f44596ba369e6b068 Mon Sep 17 00:00:00 2001
From: Allan Wang <me@allanwang.ca>
Date: Tue, 2 Jul 2019 16:29:28 -0700
Subject: Prevent horizontal swipes if html element can scroll horizontally

---
 app/src/web/ts/click_a.ts              | 10 +++---
 app/src/web/ts/horizontal_scrolling.ts | 61 ++++++++++++++++++++++++++++++++++
 app/src/web/typings/frost.d.ts         | 26 ++++++++-------
 3 files changed, 81 insertions(+), 16 deletions(-)
 create mode 100644 app/src/web/ts/horizontal_scrolling.ts

(limited to 'app/src/web')

diff --git a/app/src/web/ts/click_a.ts b/app/src/web/ts/click_a.ts
index 8d1d545b..1fd63683 100644
--- a/app/src/web/ts/click_a.ts
+++ b/app/src/web/ts/click_a.ts
@@ -91,14 +91,16 @@
         prevented = true;
     };
 
+    const _frostAllowClick = () => {
+        prevented = false;
+        clearTimeout(clickTimeout)
+    };
+
     document.addEventListener('click', _frostAClick, true);
     let clickTimeout: number | undefined = undefined;
     document.addEventListener('touchstart', () => {
         clickTimeout = setTimeout(_frostPreventClick, 400);
     }, true);
-    document.addEventListener('touchend', () => {
-        prevented = false;
-        clearTimeout(clickTimeout)
-    }, true);
+    document.addEventListener('touchend', _frostAllowClick, true);
 }).call(undefined);
 
diff --git a/app/src/web/ts/horizontal_scrolling.ts b/app/src/web/ts/horizontal_scrolling.ts
new file mode 100644
index 00000000..b104725e
--- /dev/null
+++ b/app/src/web/ts/horizontal_scrolling.ts
@@ -0,0 +1,61 @@
+(function () {
+
+  /**
+   * Go up at most [depth] times, to retrieve a parent matching the provided predicate
+   * If one is found, it is returned immediately.
+   * Otherwise, null is returned.
+   */
+  function _parentEl(el: HTMLElement, depth: number, predicate: (el: HTMLElement) => boolean): HTMLElement | null {
+    for (let i = 0; i < depth + 1; i++) {
+      if (predicate(el)) {
+        return el
+      }
+      const parent = el.parentElement;
+      if (!parent) {
+        return null
+      }
+      el = parent
+    }
+    return null
+  }
+
+  /**
+   * Check if element can scroll horizontally.
+   * We primarily rely on the overflow-x field.
+   * For performance reasons, we will check scrollWidth first to see if scrolling is a possibility
+   */
+  function _canScrollHorizontally(el: HTMLElement): boolean {
+    /*
+     * Sometimes the offsetWidth is off by < 10px. We use the multiplier
+     * since the trays are typically more than 2 times greater
+     */
+    if (el.scrollWidth > el.offsetWidth * 1.2) {
+      return true
+    }
+    const styles = window.getComputedStyle(el);
+    /*
+     * Works well in testing, but on mobile it just shows 'visible'
+     */
+    return styles.overflowX === 'scroll';
+  }
+
+  const _frostCheckHorizontalScrolling = (e: Event) => {
+    const target = e.target || e.currentTarget || e.srcElement;
+    if (!(target instanceof HTMLElement)) {
+      return
+    }
+    const scrollable = _parentEl(target, 5, _canScrollHorizontally) !== null;
+    if (scrollable) {
+      console.log('Pause horizontal scrolling');
+      Frost.allowHorizontalScrolling(false);
+    }
+  };
+
+  const _frostResetHorizontalScrolling = (e: Event) => {
+    Frost.allowHorizontalScrolling(true)
+  };
+
+  document.addEventListener('touchstart', _frostCheckHorizontalScrolling, true);
+  document.addEventListener('touchend', _frostResetHorizontalScrolling, true);
+}).call(undefined);
+
diff --git a/app/src/web/typings/frost.d.ts b/app/src/web/typings/frost.d.ts
index 8f60c9dd..ae7c97ab 100644
--- a/app/src/web/typings/frost.d.ts
+++ b/app/src/web/typings/frost.d.ts
@@ -1,27 +1,29 @@
 declare interface FrostJSI {
-    loadUrl(url: string | null): boolean
+  loadUrl(url: string | null): boolean
 
-    loadVideo(url: string | null, isGif: boolean): boolean
+  loadVideo(url: string | null, isGif: boolean): boolean
 
-    reloadBaseUrl(animate: boolean)
+  reloadBaseUrl(animate: boolean)
 
-    contextMenu(url: string | null, text: string | null)
+  contextMenu(url: string | null, text: string | null)
 
-    longClick(start: boolean)
+  longClick(start: boolean)
 
-    disableSwipeRefresh(disable: boolean)
+  disableSwipeRefresh(disable: boolean)
 
-    loadLogin()
+  loadLogin()
 
-    loadImage(imageUrl: string, text: string | null)
+  loadImage(imageUrl: string, text: string | null)
 
-    emit(flag: number)
+  emit(flag: number)
 
-    isReady()
+  isReady()
 
-    handleHtml(html: string | null)
+  handleHtml(html: string | null)
 
-    handleHeader(html: string | null)
+  handleHeader(html: string | null)
+
+  allowHorizontalScrolling(enable: boolean)
 }
 
 declare var Frost: FrostJSI;
-- 
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