Function textBufferReducer

packages/cli/src/ui/components/shared/text-buffer.ts:986–1487

(
  state: TextBufferState,
  action: TextBufferAction,
)

  | { type: 'vim_escape_insert_mode' };

export function textBufferReducer(
  state: TextBufferState,
  action: TextBufferAction,
): TextBufferState {
  const pushUndoLocal = pushUndo;

  const currentLine = (r: number): string => state.lines[r] ?? '';
  const currentLineLen = (r: number): number => cpLen(currentLine(r));

  switch (action.type) {
    case 'set_text': {
      let nextState = state;
      if (action.pushToUndo !== false) {
        nextState = pushUndoLocal(state);
      }
      const newContentLines = action.payload
        .replace(/\r\n?/g, '\n')
        .split('\n');
      const lines = newContentLines.length === 0 ? [''] : newContentLines;
      const lastNewLineIndex = lines.length - 1;
      return {
        ...nextState,
        lines,
        cursorRow: lastNewLineIndex,
        cursorCol: cpLen(lines[lastNewLineIndex] ?? ''),
        preferredCol: null,
      };
    }

    case 'insert': {
      const nextState = pushUndoLocal(state);
      const newLines = [...nextState.lines];
      let newCursorRow = nextState.cursorRow;
      let newCursorCol = nextState.cursorCol;

      const currentLine = (r: number) => newLines[r] ?? '';

      const str = stripUnsafeCharacters(
        action.payload.replace(/\r\n/g, '\n').replace(/\r/g, '\n'),
      );
      const parts = str.split('\n');
      const lineContent = currentLine(newCursorRow);
      const before = cpSlice(lineContent, 0, newCursorCol);
      const after = cpSlice(lineContent, newCursorCol);

      if (parts.length > 1) {
        newLines[newCursorRow] = before + parts[0];
        const remainingParts = parts.slice(1);
        const lastPartOriginal = remainingParts.pop() ?? '';
        newLines.splice(newCursorRow + 1, 0, ...remainingParts);
        newLines.splice(
          newCursorRow + parts.length - 1,
          0,
          lastPartOriginal + after,
        );
        newCursorRow = newCursorRow + parts.length - 1;
        newCursorCol = cpLen(lastPartOriginal);
      } else {