1 files changed, 70 insertions, 0 deletions
diff --git a/ext/js/comm/frame-offset-forwarder.js b/ext/js/comm/frame-offset-forwarder.js
new file mode 100644
index 00000000..0a0b4a18
--- /dev/null
+++ b/ext/js/comm/frame-offset-forwarder.js
@@ -0,0 +1,70 @@
+/*
+ * Copyright (C) 2020-2021  Yomichan Authors
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/* global
+ * FrameAncestryHandler
+ * api
+ */
+
+class FrameOffsetForwarder {
+    constructor(frameId) {
+        this._frameId = frameId;
+        this._frameAncestryHandler = new FrameAncestryHandler(frameId);
+    }
+
+    prepare() {
+        this._frameAncestryHandler.prepare();
+        api.crossFrame.registerHandlers([
+            ['FrameOffsetForwarder.getChildFrameRect', {async: false, handler: this._onMessageGetChildFrameRect.bind(this)}]
+        ]);
+    }
+
+    async getOffset() {
+        if (this._frameAncestryHandler.isRootFrame()) {
+            return [0, 0];
+        }
+
+        const ancestorFrameIds = await this._frameAncestryHandler.getFrameAncestryInfo();
+
+        let childFrameId = this._frameId;
+        const promises = [];
+        for (const frameId of ancestorFrameIds) {
+            promises.push(api.crossFrame.invoke(frameId, 'FrameOffsetForwarder.getChildFrameRect', {frameId: childFrameId}));
+            childFrameId = frameId;
+        }
+
+        const results = await Promise.all(promises);
+
+        let xOffset = 0;
+        let yOffset = 0;
+        for (const {x, y} of results) {
+            xOffset += x;
+            yOffset += y;
+        }
+        return [xOffset, yOffset];
+    }
+
+    // Private
+
+    _onMessageGetChildFrameRect({frameId}) {
+        const frameElement = this._frameAncestryHandler.getChildFrameElement(frameId);
+        if (frameElement === null) { return null; }
+
+        const {x, y, width, height} = frameElement.getBoundingClientRect();
+        return {x, y, width, height};
+    }
+}