numolus/app/frontend/composables/useKeyboardPointMode.ts

/**
 * Keyboard-driven counterpart to the mouse "point mode" already in
 * store.pointClick/pointDrag (click/drag a grid cell while editing a
 * formula to insert its reference): arrow keys pick a cell/range the same
 * way, without leaving the keyboard.
 *
 * Only takes over the arrow keys when the caret sits right after a token
 * that expects a new operand -- the leading '=', an operator, '(', or the
 * ';' argument separator -- exactly like Excel/Numbers decide the same
 * thing. Anywhere else (mid-identifier, mid-number, ...) arrow keys keep
 * moving the text caret as normal; editing an existing formula by hand
 * still works.
 *
 * First press of a fresh chain steps one cell from `home` (the cell being
 * edited) in the pressed direction. Further plain-arrow presses move that
 * single cell on; holding Shift instead grows a range from the chain's
 * first cell (its `anchor`) to wherever the focus has moved to, the same
 * "collapse on a plain move, grow from the anchor on a extending one"
 * convention TableGrid's own grid-cell navigate() already uses.
 */
import { useDocument } from '../store/document';

const ARROW_DELTA: Record<string, [number, number]> = {
  ArrowUp: [0, -1],
  ArrowDown: [0, 1],
  ArrowLeft: [-1, 0],
  ArrowRight: [1, 0],
};

const OPERAND_BOUNDARY = new Set(['=', '+', '-', '*', '/', '^', '&', '<', '>', '(', ';']);

export function useKeyboardPointMode() {
  const store = useDocument();
  let anchor: { tableId: string; col: number; row: number } | null = null;
  let focus: { col: number; row: number } | null = null;

  /** Ends the current chain (if any) -- call whenever the editor's text is
   *  typed into directly, the caret is repositioned by a mouse click, or a
   *  new edit session begins, exactly the same triggers that already reset
   *  the mouse point-mode's own "replace on next click" window
   *  (store.noteFormulaTyped()). */
  function reset() {
    anchor = null;
    focus = null;
  }

  function canStartAt(text: string, caret: number): boolean {
    if (!text.startsWith('=')) return false;
    const prev = text[caret - 1];
    return prev !== undefined && OPERAND_BOUNDARY.has(prev);
  }

  /** Handles one ArrowUp/Down/Left/Right press (optionally Shift-extended).
   *  Returns true if it took over the key (caller must preventDefault +
   *  stopPropagation); false if normal caret movement should happen
   *  instead. `home` is the cell being edited. */
  function handleArrowKey(
    e: KeyboardEvent,
    tableId: string,
    home: { col: number; row: number },
    text: string,
    caret: number,
  ): boolean {
    const delta = ARROW_DELTA[e.key];
    if (!delta) return false;
    const t = store.tableById(tableId);
    if (!t) return false;
    const clampC = (c: number) => Math.max(0, Math.min(t.cols - 1, c));
    const clampR = (r: number) => Math.max(0, Math.min(t.rows - 1, r));

    if (!anchor || anchor.tableId !== tableId) {
      if (!canStartAt(text, caret)) return false;
      const target = { col: clampC(home.col + delta[0]), row: clampR(home.row + delta[1]) };
      anchor = { tableId, ...target };
      focus = target;
      store.pointClick(tableId, target.col, target.row);
      return true;
    }

    const base = focus ?? anchor;
    const next = { col: clampC(base.col + delta[0]), row: clampR(base.row + delta[1]) };
    if (e.shiftKey) {
      focus = next;
      store.pointDrag(tableId, anchor.col, anchor.row, focus.col, focus.row);
    } else {
      anchor = { tableId, ...next };
      focus = next;
      store.pointClick(tableId, next.col, next.row);
    }
    return true;
  }

  return { handleArrowKey, reset };
}