Fix bug where single line inserts were deleting all text after the in… (#1114)

packages/cli/src/ui/components/shared/text-buffer.test.ts

@@ -173,6 +173,21 @@ describe('useTextBuffer', () => {
       expect(state.visualCursor).toEqual([0, 2]);
     });
 
+    it('insert: should insert text in the middle of a line', () => {
+      const { result } = renderHook(() =>
+        useTextBuffer({
+          initialText: 'abc',
+          viewport,
+          isValidPath: () => false,
+        }),
+      );
+      act(() => result.current.move('right'));
+      act(() => result.current.insert('-NEW-'));
+      const state = getBufferState(result);
+      expect(state.text).toBe('a-NEW-bc');
+      expect(state.cursor).toEqual([0, 6]);
+    });
+
     it('newline: should create a new line and move cursor', () => {
       const { result } = renderHook(() =>
         useTextBuffer({

packages/cli/src/ui/components/shared/text-buffer.ts

@@ -635,9 +635,9 @@ export function useTextBuffer({
           const lineContent = currentLine(newCursorRow);
           const before = cpSlice(lineContent, 0, newCursorCol);
           const after = cpSlice(lineContent, newCursorCol);
-          newLines[newCursorRow] = before + parts[0];
 
           if (parts.length > 1) {
+            newLines[newCursorRow] = before + parts[0];
             const remainingParts = parts.slice(1);
             const lastPartOriginal = remainingParts.pop() ?? '';
             newLines.splice(newCursorRow + 1, 0, ...remainingParts);
@@ -649,6 +649,8 @@ export function useTextBuffer({
             newCursorRow = newCursorRow + parts.length - 1;
             newCursorCol = cpLen(lastPartOriginal);
           } else {
+            newLines[newCursorRow] = before + parts[0] + after;
+
             newCursorCol = cpLen(before) + cpLen(parts[0]);
           }
         } else if (op.type === 'backspace') {