import { TextSelection } from "prosemirror-state";
import { UxCommand } from "../constants";
import { Bias, CartesianAxis, Command, DirString } from "../types";
import { WedgeSelection } from "./WedgeSelection";

/**
 * Build a command that handles the user intent of moving the cursor in a
 * particular direction (up / down / left / right) by switching to a wedge
 * selection if the current selection is at a barrier.
 */
function arrow(axis: CartesianAxis, bias: Bias): Command {
  const dirStr: DirString =
    axis == CartesianAxis.VERTICAL ? (bias == Bias.FORWARD ? "down" : "up") : bias == Bias.FORWARD ? "right" : "left";

  return (state, dispatch, view) => {
    const sel = state.selection;
    let $start = bias == Bias.FORWARD ? sel.$to : sel.$from;
    let mustMove = sel.empty;
    if (sel instanceof TextSelection) {
      if (view !== undefined && !view.endOfTextblock(dirStr)) {
        return false;
      }
      mustMove = false;
      $start = state.doc.resolve(bias == Bias.FORWARD ? $start.after() : $start.before());
    }
    const newSelection = WedgeSelection.findFrom($start, bias == Bias.FORWARD ? 1 : -1, undefined, mustMove);
    if (newSelection == null) {
      return false;
    }
    if (dispatch !== undefined) {
      dispatch(state.tr.setSelection(newSelection));
    }
    return true;
  };
}

export const tryWedgeUp = arrow(CartesianAxis.VERTICAL, Bias.BACKWARD);
export const tryWedgeRight = arrow(CartesianAxis.HORIZONTAL, Bias.FORWARD);
export const tryWedgeDown = arrow(CartesianAxis.VERTICAL, Bias.FORWARD);
export const tryWedgeLeft = arrow(CartesianAxis.HORIZONTAL, Bias.BACKWARD);

export const ux = {
  [UxCommand.ArrowDown]: tryWedgeDown,
  [UxCommand.ArrowLeft]: tryWedgeLeft,
  [UxCommand.ArrowRight]: tryWedgeRight,
  [UxCommand.ArrowUp]: tryWedgeUp
};