feat($swipe): Refactor swipe logic from ngSwipe to $swipe service.

This new service is used by the ngSwipeLeft/Right directives, and by the
separate ngCarousel and swipe-to-delete directives which are under
development.

1 files changed, 136 insertions, 0 deletions

diff --git a/src/ngMobile/swipe.js b/src/ngMobile/swipe.js
new file mode 100644
index 00000000..612d65fd
--- /dev/null
+++ b/src/ngMobile/swipe.js
@@ -0,0 +1,136 @@
+'use strict';
+
+    /**
+     * @ngdoc object
+     * @name ngMobile.$swipe
+     *
+     * @description
+     * The `$swipe` service is a service that abstracts the messier details of hold-and-drag swipe
+     * behavior, to make implementing swipe-related directives more convenient.
+     *
+     * It is used by the `ngSwipeLeft` and `ngSwipeRight` directives in `ngMobile`, and by
+     * `ngCarousel` in a separate component.
+     *
+     * # Usage
+     * The `$swipe` service is an object with a single method: `bind`. `bind` takes an element
+     * which is to be watched for swipes, and an object with four handler functions. See the
+     * documentation for `bind` below.
+     */
+
+ngMobile.factory('$swipe', [function() {
+  // The total distance in any direction before we make the call on swipe vs. scroll.
+  var MOVE_BUFFER_RADIUS = 10;
+
+  function getCoordinates(event) {
+    var touches = event.touches && event.touches.length ? event.touches : [event];
+    var e = (event.changedTouches && event.changedTouches[0]) ||
+        (event.originalEvent && event.originalEvent.changedTouches &&
+            event.originalEvent.changedTouches[0]) ||
+        touches[0].originalEvent || touches[0];
+
+    return {
+      x: e.clientX,
+      y: e.clientY
+    };
+  }
+
+  return {
+    /**
+     * @ngdoc method
+     * @name ngMobile.$swipe#bind
+     * @methodOf ngMobile.$swipe
+     *
+     * @description
+     * The main method of `$swipe`. It takes an element to be watched for swipe motions, and an
+     * object containing event handlers.
+     *
+     * The four events are `start`, `move`, `end`, and `cancel`. `start`, `move`, and `end`
+     * receive as a parameter a coordinates object of the form `{ x: 150, y: 310 }`.
+     *
+     * `start` is called on either `mousedown` or `touchstart`. After this event, `$swipe` is
+     * watching for `touchmove` or `mousemove` events. These events are ignored until the total
+     * distance moved in either dimension exceeds a small threshold.
+     *
+     * Once this threshold is exceeded, either the horizontal or vertical delta is greater.
+     * - If the horizontal distance is greater, this is a swipe and `move` and `end` events follow.
+     * - If the vertical distance is greater, this is a scroll, and we let the browser take over.
+     *   A `cancel` event is sent.
+     *
+     * `move` is called on `mousemove` and `touchmove` after the above logic has determined that
+     * a swipe is in progress.
+     *
+     * `end` is called when a swipe is successfully completed with a `touchend` or `mouseup`.
+     *
+     * `cancel` is called either on a `touchcancel` from the browser, or when we begin scrolling
+     * as described above.
+     *
+     */
+    bind: function(element, eventHandlers) {
+      // Absolute total movement, used to control swipe vs. scroll.
+      var totalX, totalY;
+      // Coordinates of the start position.
+      var startCoords;
+      // Last event's position.
+      var lastPos;
+      // Whether a swipe is active.
+      var active = false;
+
+      element.bind('touchstart mousedown', function(event) {
+        startCoords = getCoordinates(event);
+        active = true;
+        totalX = 0;
+        totalY = 0;
+        lastPos = startCoords;
+        eventHandlers['start'] && eventHandlers['start'](startCoords);
+      });
+
+      element.bind('touchcancel', function(event) {
+        active = false;
+        eventHandlers['cancel'] && eventHandlers['cancel']();
+      });
+
+      element.bind('touchmove mousemove', function(event) {
+        if (!active) return;
+
+        // Android will send a touchcancel if it thinks we're starting to scroll.
+        // So when the total distance (+ or - or both) exceeds 10px in either direction,
+        // we either:
+        // - On totalX > totalY, we send preventDefault() and treat this as a swipe.
+        // - On totalY > totalX, we let the browser handle it as a scroll.
+
+        if (!startCoords) return;
+        var coords = getCoordinates(event);
+
+        totalX += Math.abs(coords.x - lastPos.x);
+        totalY += Math.abs(coords.y - lastPos.y);
+
+        lastPos = coords;
+
+        if (totalX < MOVE_BUFFER_RADIUS && totalY < MOVE_BUFFER_RADIUS) {
+          return;
+        }
+
+        // One of totalX or totalY has exceeded the buffer, so decide on swipe vs. scroll.
+        if (totalY > totalX) {
+          // Allow native scrolling to take over.
+          active = false;
+          eventHandlers['cancel'] && eventHandlers['cancel']();
+          return;
+        } else {
+          // Prevent the browser from scrolling.
+          event.preventDefault();
+
+          eventHandlers['move'] && eventHandlers['move'](coords);
+        }
+      });
+
+      element.bind('touchend mouseup', function(event) {
+        if (!active) return;
+        active = false;
+        eventHandlers['end'] && eventHandlers['end'](getCoordinates(event));
+      });
+    }
+  };
+}]);
+
+