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node_modules/react-native-web/dist/vendor/react-native/ViewabilityHelper/index.js

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+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * 
+ * @format
+ */
+'use strict';
+
+function ownKeys(object, enumerableOnly) { var keys = Object.keys(object); if (Object.getOwnPropertySymbols) { var symbols = Object.getOwnPropertySymbols(object); if (enumerableOnly) symbols = symbols.filter(function (sym) { return Object.getOwnPropertyDescriptor(object, sym).enumerable; }); keys.push.apply(keys, symbols); } return keys; }
+
+function _objectSpread(target) { for (var i = 1; i < arguments.length; i++) { var source = arguments[i] != null ? arguments[i] : {}; if (i % 2) { ownKeys(Object(source), true).forEach(function (key) { _defineProperty(target, key, source[key]); }); } else if (Object.getOwnPropertyDescriptors) { Object.defineProperties(target, Object.getOwnPropertyDescriptors(source)); } else { ownKeys(Object(source)).forEach(function (key) { Object.defineProperty(target, key, Object.getOwnPropertyDescriptor(source, key)); }); } } return target; }
+
+function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }
+
+import invariant from 'fbjs/lib/invariant';
+
+/**
+ * A Utility class for calculating viewable items based on current metrics like scroll position and
+ * layout.
+ *
+ * An item is said to be in a "viewable" state when any of the following
+ * is true for longer than `minimumViewTime` milliseconds (after an interaction if `waitForInteraction`
+ * is true):
+ *
+ * - Occupying >= `viewAreaCoveragePercentThreshold` of the view area XOR fraction of the item
+ *   visible in the view area >= `itemVisiblePercentThreshold`.
+ * - Entirely visible on screen
+ */
+var ViewabilityHelper =
+/*#__PURE__*/
+function () {
+  /* $FlowFixMe(>=0.63.0 site=react_native_fb) This comment suppresses an error
+   * found when Flow v0.63 was deployed. To see the error delete this comment
+   * and run Flow. */
+  function ViewabilityHelper(config) {
+    if (config === void 0) {
+      config = {
+        viewAreaCoveragePercentThreshold: 0
+      };
+    }
+
+    this._hasInteracted = false;
+    this._timers = new Set();
+    this._viewableIndices = [];
+    this._viewableItems = new Map();
+    this._config = config;
+  }
+  /**
+   * Cleanup, e.g. on unmount. Clears any pending timers.
+   */
+
+
+  var _proto = ViewabilityHelper.prototype;
+
+  _proto.dispose = function dispose() {
+    this._timers.forEach(clearTimeout);
+  }
+  /**
+   * Determines which items are viewable based on the current metrics and config.
+   */
+  ;
+
+  _proto.computeViewableItems = function computeViewableItems(itemCount, scrollOffset, viewportHeight, getFrameMetrics, renderRange) {
+    var _this$_config = this._config,
+        itemVisiblePercentThreshold = _this$_config.itemVisiblePercentThreshold,
+        viewAreaCoveragePercentThreshold = _this$_config.viewAreaCoveragePercentThreshold;
+    var viewAreaMode = viewAreaCoveragePercentThreshold != null;
+    var viewablePercentThreshold = viewAreaMode ? viewAreaCoveragePercentThreshold : itemVisiblePercentThreshold;
+    invariant(viewablePercentThreshold != null && itemVisiblePercentThreshold != null !== (viewAreaCoveragePercentThreshold != null), 'Must set exactly one of itemVisiblePercentThreshold or viewAreaCoveragePercentThreshold');
+    var viewableIndices = [];
+
+    if (itemCount === 0) {
+      return viewableIndices;
+    }
+
+    var firstVisible = -1;
+
+    var _ref = renderRange || {
+      first: 0,
+      last: itemCount - 1
+    },
+        first = _ref.first,
+        last = _ref.last;
+
+    if (last >= itemCount) {
+      console.warn('Invalid render range computing viewability ' + JSON.stringify({
+        renderRange: renderRange,
+        itemCount: itemCount
+      }));
+      return [];
+    }
+
+    for (var idx = first; idx <= last; idx++) {
+      var metrics = getFrameMetrics(idx);
+
+      if (!metrics) {
+        continue;
+      }
+
+      var top = metrics.offset - scrollOffset;
+      var bottom = top + metrics.length;
+
+      if (top < viewportHeight && bottom > 0) {
+        firstVisible = idx;
+
+        if (_isViewable(viewAreaMode, viewablePercentThreshold, top, bottom, viewportHeight, metrics.length)) {
+          viewableIndices.push(idx);
+        }
+      } else if (firstVisible >= 0) {
+        break;
+      }
+    }
+
+    return viewableIndices;
+  }
+  /**
+   * Figures out which items are viewable and how that has changed from before and calls
+   * `onViewableItemsChanged` as appropriate.
+   */
+  ;
+
+  _proto.onUpdate = function onUpdate(itemCount, scrollOffset, viewportHeight, getFrameMetrics, createViewToken, onViewableItemsChanged, renderRange) {
+    var _this = this;
+
+    if (this._config.waitForInteraction && !this._hasInteracted || itemCount === 0 || !getFrameMetrics(0)) {
+      return;
+    }
+
+    var viewableIndices = [];
+
+    if (itemCount) {
+      viewableIndices = this.computeViewableItems(itemCount, scrollOffset, viewportHeight, getFrameMetrics, renderRange);
+    }
+
+    if (this._viewableIndices.length === viewableIndices.length && this._viewableIndices.every(function (v, ii) {
+      return v === viewableIndices[ii];
+    })) {
+      // We might get a lot of scroll events where visibility doesn't change and we don't want to do
+      // extra work in those cases.
+      return;
+    }
+
+    this._viewableIndices = viewableIndices;
+
+    if (this._config.minimumViewTime) {
+      var handle = setTimeout(function () {
+        _this._timers.delete(handle);
+
+        _this._onUpdateSync(viewableIndices, onViewableItemsChanged, createViewToken);
+      }, this._config.minimumViewTime);
+
+      this._timers.add(handle);
+    } else {
+      this._onUpdateSync(viewableIndices, onViewableItemsChanged, createViewToken);
+    }
+  }
+  /**
+   * clean-up cached _viewableIndices to evaluate changed items on next update
+   */
+  ;
+
+  _proto.resetViewableIndices = function resetViewableIndices() {
+    this._viewableIndices = [];
+  }
+  /**
+   * Records that an interaction has happened even if there has been no scroll.
+   */
+  ;
+
+  _proto.recordInteraction = function recordInteraction() {
+    this._hasInteracted = true;
+  };
+
+  _proto._onUpdateSync = function _onUpdateSync( // $FlowFixMe
+  viewableIndicesToCheck, // $FlowFixMe
+  onViewableItemsChanged, // $FlowFixMe
+  createViewToken) {
+    var _this2 = this;
+
+    // Filter out indices that have gone out of view since this call was scheduled.
+    viewableIndicesToCheck = viewableIndicesToCheck.filter(function (ii) {
+      return _this2._viewableIndices.includes(ii);
+    });
+    var prevItems = this._viewableItems;
+    var nextItems = new Map(viewableIndicesToCheck.map(function (ii) {
+      var viewable = createViewToken(ii, true);
+      return [viewable.key, viewable];
+    }));
+    var changed = [];
+
+    for (var _iterator = nextItems, _isArray = Array.isArray(_iterator), _i = 0, _iterator = _isArray ? _iterator : _iterator[Symbol.iterator]();;) {
+      var _ref2;
+
+      if (_isArray) {
+        if (_i >= _iterator.length) break;
+        _ref2 = _iterator[_i++];
+      } else {
+        _i = _iterator.next();
+        if (_i.done) break;
+        _ref2 = _i.value;
+      }
+
+      var _ref4 = _ref2,
+          key = _ref4[0],
+          viewable = _ref4[1];
+
+      if (!prevItems.has(key)) {
+        changed.push(viewable);
+      }
+    }
+
+    for (var _iterator2 = prevItems, _isArray2 = Array.isArray(_iterator2), _i2 = 0, _iterator2 = _isArray2 ? _iterator2 : _iterator2[Symbol.iterator]();;) {
+      var _ref3;
+
+      if (_isArray2) {
+        if (_i2 >= _iterator2.length) break;
+        _ref3 = _iterator2[_i2++];
+      } else {
+        _i2 = _iterator2.next();
+        if (_i2.done) break;
+        _ref3 = _i2.value;
+      }
+
+      var _ref5 = _ref3,
+          _key = _ref5[0],
+          _viewable = _ref5[1];
+
+      if (!nextItems.has(_key)) {
+        changed.push(_objectSpread({}, _viewable, {
+          isViewable: false
+        }));
+      }
+    }
+
+    if (changed.length > 0) {
+      this._viewableItems = nextItems;
+      onViewableItemsChanged({
+        viewableItems: Array.from(nextItems.values()),
+        changed: changed,
+        viewabilityConfig: this._config
+      });
+    }
+  };
+
+  return ViewabilityHelper;
+}();
+
+function _isViewable(viewAreaMode, viewablePercentThreshold, top, bottom, viewportHeight, itemLength) {
+  if (_isEntirelyVisible(top, bottom, viewportHeight)) {
+    return true;
+  } else {
+    var pixels = _getPixelsVisible(top, bottom, viewportHeight);
+
+    var percent = 100 * (viewAreaMode ? pixels / viewportHeight : pixels / itemLength);
+    return percent >= viewablePercentThreshold;
+  }
+}
+
+function _getPixelsVisible(top, bottom, viewportHeight) {
+  var visibleHeight = Math.min(bottom, viewportHeight) - Math.max(top, 0);
+  return Math.max(0, visibleHeight);
+}
+
+function _isEntirelyVisible(top, bottom, viewportHeight) {
+  return top >= 0 && bottom <= viewportHeight && bottom > top;
+}
+
+export default ViewabilityHelper;