Set caret inside chemical expression in Mathjax (#1763)

ts/editable/Mathjax.svelte

@@ -41,11 +41,11 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
     let image: HTMLImageElement;
 
-    export function moveCaretAfter(): void {
+    export function moveCaretAfter(position?: [number, number]): void {
         // This should trigger a focusing of the Mathjax Handle
         image.dispatchEvent(
             new CustomEvent("movecaretafter", {
-                detail: image,
+                detail: { image, position },
                 bubbles: true,
                 composed: true,
             }),

ts/editable/mathjax-element.ts

@@ -121,7 +121,15 @@ export const Mathjax: DecoratedElementConstructor = class Mathjax
         });
 
         if (this.hasAttribute("focusonmount")) {
-            this.component.moveCaretAfter();
+            let position: [number, number] | undefined = undefined;
+
+            if (this.getAttribute("focusonmount")!.length > 0) {
+                position = this.getAttribute("focusonmount")!
+                    .split(",")
+                    .map(Number) as [number, number];
+            }
+
+            this.component.moveCaretAfter(position);
         }
 
         this.setAttribute("contentEditable", "false");

ts/editor/code-mirror.ts

@@ -52,9 +52,12 @@ export const gutterOptions: CodeMirror.EditorConfiguration = {
     foldGutter: true,
 };
 
-export function focusAndCaretAfter(editor: CodeMirror.Editor): void {
+export function focusAndSetCaret(
+    editor: CodeMirror.Editor,
+    position: CodeMirror.Position = { line: editor.lineCount(), ch: 0 },
+): void {
     editor.focus();
-    editor.setCursor(editor.lineCount(), 0);
+    editor.setCursor(position);
 }
 
 interface OpenCodeMirrorOptions {

ts/editor/editor-toolbar/LatexButton.svelte

@@ -35,7 +35,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     }
 
     function onMathjaxChemistry(): void {
-        surround("<anki-mathjax focusonmount>\\ce{", "}</anki-mathjax>");
+        surround('<anki-mathjax focusonmount="0,4">\\ce{', "}</anki-mathjax>");
     }
 
     function onLatex(): void {

ts/editor/mathjax-overlay/MathjaxEditor.svelte

@@ -10,7 +10,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     import * as tr from "../../lib/ftl";
     import { noop } from "../../lib/functional";
     import { getPlatformString } from "../../lib/shortcuts";
-    import { baseOptions, focusAndCaretAfter, latex } from "../code-mirror";
+    import { baseOptions, focusAndSetCaret, latex } from "../code-mirror";
     import type { CodeMirrorAPI } from "../CodeMirror.svelte";
     import CodeMirror from "../CodeMirror.svelte";
 
@@ -33,15 +33,18 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
         mode: latex,
     };
 
+    /* These are not reactive, but only operate on initialization */
+    export let position: CodeMirrorLib.Position | undefined = undefined;
     export let selectAll: boolean;
 
     const dispatch = createEventDispatcher();
 
     let codeMirror = {} as CodeMirrorAPI;
 
-    onMount(() =>
-        codeMirror.editor.then((editor) => {
-            focusAndCaretAfter(editor);
+    onMount(async () => {
+        const editor = await codeMirror.editor;
+
+        focusAndSetCaret(editor, position);
 
         if (selectAll) {
             editor.execCommand("selectAll");
@@ -83,8 +86,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
                 direction = undefined;
             },
         );
-        }),
-    );
+    });
 
     /**
      * Escape characters which are technically legal in Mathjax, but confuse HTML.

ts/editor/mathjax-overlay/MathjaxHandle.svelte

@@ -3,6 +3,7 @@ Copyright: Ankitects Pty Ltd and contributors
 License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 -->
 <script lang="ts">
+    import type CodeMirrorLib from "codemirror";
     import { onDestroy, onMount, tick } from "svelte";
     import { writable } from "svelte/store";
 
@@ -26,9 +27,15 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     let allow = noop;
     let unsubscribe = noop;
 
-    function showHandle(image: HTMLImageElement): void {
-        allow = preventResubscription();
+    let selectAll = false;
+    let position: CodeMirrorLib.Position | undefined = undefined;
 
+    function showHandle(image: HTMLImageElement, pos?: CodeMirrorLib.Position): void {
+        allow = preventResubscription();
+        position = pos;
+
+        /* Setting the activeImage and mathjaxElement to a non-nullish value is
+         * what triggers the Mathjax editor to show */
         activeImage = image;
         mathjaxElement = activeImage.closest(Mathjax.tagName)!;
 
@@ -38,8 +45,6 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
         });
     }
 
-    let selectAll = false;
-
     function placeHandle(after: boolean): void {
         editable.focusHandler.flushCaret();
 
@@ -52,6 +57,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
     async function resetHandle(): Promise<void> {
         selectAll = false;
+        position = undefined;
 
         if (activeImage && mathjaxElement) {
             unsubscribe();
@@ -72,9 +78,20 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
     async function showAutofocusHandle({
         detail,
-    }: CustomEvent<HTMLImageElement>): Promise<void> {
+    }: CustomEvent<{
+        image: HTMLImageElement;
+        position?: [number, number];
+    }>): Promise<void> {
+        let position: CodeMirrorLib.Position | undefined = undefined;
+
         await resetHandle();
-        showHandle(detail);
+
+        if (detail.position) {
+            const [line, ch] = detail.position;
+            position = { line, ch };
+        }
+
+        showHandle(detail.image, position);
     }
 
     async function showSelectAll({
@@ -138,6 +155,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
             element={mathjaxElement}
             {code}
             {selectAll}
+            {position}
             bind:updateSelection
             on:reset={resetHandle}
             on:moveoutstart={() => {

ts/editor/mathjax-overlay/MathjaxMenu.svelte

@@ -3,6 +3,7 @@ Copyright: Ankitects Pty Ltd and contributors
 License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 -->
 <script lang="ts">
+    import type CodeMirrorLib from "codemirror";
     import { createEventDispatcher } from "svelte";
     import type { Writable } from "svelte/store";
 
@@ -15,7 +16,9 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
 
     export let element: Element;
     export let code: Writable<string>;
+
     export let selectAll: boolean;
+    export let position: CodeMirrorLib.Position | undefined;
 
     const acceptShortcut = "Enter";
     const newlineShortcut = "Shift+Enter";
@@ -40,6 +43,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
             {newlineShortcut}
             {code}
             {selectAll}
+            {position}
             on:blur={() => dispatch("reset")}
             on:moveoutstart
             on:moveoutend