fix: codemirror util

frontend/src/hooks/useCodeMirrorInsert.ts

@@ -0,0 +1,51 @@
+import { useCallback } from 'react'
+
+/**
+ * Ref shape for @uiw/react-codemirror (view/state not in package types).
+ * Use with: ref={editorRef} and type editorRef as React.MutableRefObject<CodeMirrorEditorRef | null>.
+ */
+export type CodeMirrorEditorRef = {
+    view: {
+        state: {
+            doc: { length: number; toString(): string }
+            selection: { main: { from: number } }
+        }
+        dispatch: (arg: { changes: { from: number; to: number; insert: string } }) => void
+    }
+}
+
+export type InsertPosition = 'prepend' | 'append' | 'cursor'
+
+/**
+ * Returns a stable insertAt(insertText, mode) that inserts text into the CodeMirror
+ * editor at the given position (prepend, append, or cursor), then calls onChange
+ * with the new content. Falls back to string concatenation when the editor ref
+ * is not yet mounted.
+ */
+export function useCodeMirrorInsert(
+    editorRef: React.RefObject<CodeMirrorEditorRef | null>,
+    currentContent: string,
+    onChange: (value: string) => void
+): (insertText: string, mode: InsertPosition) => void {
+    return useCallback(
+        (insertText: string, mode: InsertPosition) => {
+            const ref = editorRef.current
+            if (ref?.view) {
+                const view = ref.view
+                const doc = view.state.doc
+                const len = doc.length
+                const from =
+                    mode === 'prepend' ? 0 : mode === 'append' ? len : view.state.selection.main.from
+                view.dispatch({ changes: { from, to: from, insert: insertText } })
+                onChange(view.state.doc.toString())
+                return
+            }
+            if (mode === 'prepend') {
+                onChange(insertText + currentContent)
+            } else {
+                onChange(currentContent + insertText)
+            }
+        },
+        [currentContent, onChange]
+    )
+}