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app/src/vendor/muuri-src/utils/getOffsetDiff.js

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+/**
+ * Copyright (c) 2015-present, Haltu Oy
+ * Released under the MIT license
+ * https://github.com/haltu/muuri/blob/master/LICENSE.md
+ */
+
+import getContainingBlock from './getContainingBlock';
+import getStyleAsFloat from './getStyleAsFloat';
+
+var offsetA = {};
+var offsetB = {};
+var offsetDiff = {};
+
+/**
+ * Returns the element's document offset, which in practice means the vertical
+ * and horizontal distance between the element's northwest corner and the
+ * document's northwest corner. Note that this function always returns the same
+ * object so be sure to read the data from it instead using it as a reference.
+ *
+ * @param {(Document|Element|Window)} element
+ * @param {Object} [offsetData]
+ *   - Optional data object where the offset data will be inserted to. If not
+ *     provided a new object will be created for the return data.
+ * @returns {Object}
+ */
+function getOffset(element, offsetData) {
+  var offset = offsetData || {};
+  var rect;
+
+  // Set up return data.
+  offset.left = 0;
+  offset.top = 0;
+
+  // Document's offsets are always 0.
+  if (element === document) return offset;
+
+  // Add viewport scroll left/top to the respective offsets.
+  offset.left = window.pageXOffset || 0;
+  offset.top = window.pageYOffset || 0;
+
+  // Window's offsets are the viewport scroll left/top values.
+  if (element.self === window.self) return offset;
+
+  // Add element's client rects to the offsets.
+  rect = element.getBoundingClientRect();
+  offset.left += rect.left;
+  offset.top += rect.top;
+
+  // Exclude element's borders from the offset.
+  offset.left += getStyleAsFloat(element, 'border-left-width');
+  offset.top += getStyleAsFloat(element, 'border-top-width');
+
+  return offset;
+}
+
+/**
+ * Calculate the offset difference two elements.
+ *
+ * @param {HTMLElement} elemA
+ * @param {HTMLElement} elemB
+ * @param {Boolean} [compareContainingBlocks=false]
+ *   - When this is set to true the containing blocks of the provided elements
+ *     will be used for calculating the difference. Otherwise the provided
+ *     elements will be compared directly.
+ * @returns {Object}
+ */
+export default function getOffsetDiff(elemA, elemB, compareContainingBlocks) {
+  offsetDiff.left = 0;
+  offsetDiff.top = 0;
+
+  // If elements are same let's return early.
+  if (elemA === elemB) return offsetDiff;
+
+  // Compare containing blocks if necessary.
+  if (compareContainingBlocks) {
+    elemA = getContainingBlock(elemA);
+    elemB = getContainingBlock(elemB);
+
+    // If containing blocks are identical, let's return early.
+    if (elemA === elemB) return offsetDiff;
+  }
+
+  // Finally, let's calculate the offset diff.
+  getOffset(elemA, offsetA);
+  getOffset(elemB, offsetB);
+  offsetDiff.left = offsetB.left - offsetA.left;
+  offsetDiff.top = offsetB.top - offsetA.top;
+
+  return offsetDiff;
+}