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diff --git a/devtools/client/responsive/utils/orientation.js b/devtools/client/responsive/utils/orientation.js
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+const {
+  PORTRAIT_PRIMARY,
+  LANDSCAPE_PRIMARY,
+} = require("resource://devtools/client/responsive/constants.js");
+
+/**
+ * Helper that gets the screen orientation of the device displayed in the RDM viewport.
+ * This function take in both a device and viewport object and an optional rotated angle.
+ * If a rotated angle is passed, then we calculate what the orientation type of the device
+ * would be in relation to its current orientation. Otherwise, return the current
+ * orientation and angle.
+ *
+ * @param {Object} device
+ *        The device whose content is displayed in the viewport. Used to determine the
+ *        primary orientation.
+ * @param {Object} viewport
+ *        The viewport displaying device content. Used to determine the current
+ *        orientation type of the device while in RDM.
+ * @param {Number|null} angleToRotateTo
+ *        Optional. The rotated angle specifies the degree to which the device WILL be
+ *        turned to. If undefined, then only return the current orientation and angle
+ *        of the device.
+ * @return {Object} the orientation of the device.
+ */
+function getOrientation(device, viewport, angleToRotateTo = null) {
+  const { width: deviceWidth, height: deviceHeight } = device;
+  const { width: viewportWidth, height: viewportHeight } = viewport;
+
+  // Determine the primary orientation of the device screen.
+  const primaryOrientation =
+    deviceHeight >= deviceWidth ? PORTRAIT_PRIMARY : LANDSCAPE_PRIMARY;
+
+  // Determine the current orientation of the device screen.
+  const currentOrientation =
+    viewportHeight >= viewportWidth ? PORTRAIT_PRIMARY : LANDSCAPE_PRIMARY;
+
+  // Calculate the orientation angle of the device.
+  let angle;
+
+  if (typeof angleToRotateTo === "number") {
+    angle = angleToRotateTo;
+  } else if (currentOrientation !== primaryOrientation) {
+    angle = 90;
+  } else {
+    angle = 0;
+  }
+
+  // Calculate the orientation type of the device.
+  let orientationType = currentOrientation;
+
+  // If the viewport orientation is different from the primary orientation and the angle
+  // to rotate to is 0, then we are moving the device orientation back to its primary
+  // orientation.
+  if (currentOrientation !== primaryOrientation && angleToRotateTo === 0) {
+    orientationType = primaryOrientation;
+  } else if (angleToRotateTo === 90 || angleToRotateTo === 270) {
+    if (currentOrientation.includes("portrait")) {
+      orientationType = LANDSCAPE_PRIMARY;
+    } else if (currentOrientation.includes("landscape")) {
+      orientationType = PORTRAIT_PRIMARY;
+    }
+  }
+
+  return {
+    type: orientationType,
+    angle,
+  };
+}
+
+exports.getOrientation = getOrientation;