import { setBlockType } from "prosemirror-commands";
import { EditorState } from "prosemirror-state";
import { UxCommand } from "../constants";
import { closest } from "../pquery";
import { HeadingAttrs, schema } from "../schema";
import { Command, Dispatch } from "../types";

/**
 * Defines the behaviour for pressing 'backspace' at the start of a heading.
 *
 * It attempts to convert the heading to a paragraph.
 */
export function escapeFromStart(state: EditorState, dispatch?: Dispatch) {
  const selection = state.selection;

  // Escaping a heading only works on an empty selection.
  if (!selection.empty) {
    return false;
  }

  const $pos = selection.$from;

  // Verify we're at the start of the heading.
  if ($pos.start($pos.depth) !== $pos.pos) {
    return false;
  }

  const parent = $pos.node($pos.depth);

  // Ensure we're actually in a heading.
  if (parent.type !== schema.nodes.h) {
    return false;
  }

  // Ensure we can actually replace it with a paragraph (taken from
  // textblockTypeInputRule, and probably a little overkill).
  if (!$pos.node(-1).canReplaceWith($pos.index(-1), $pos.indexAfter(-1), schema.nodes.h)) {
    return false;
  }

  if (dispatch !== undefined) dispatch(state.tr.setNodeMarkup($pos.before(), schema.nodes.p));
  return true;
}

const toggleHeading = (level: number): Command => (state, dispatch) => {
  const { $anchor } = state.selection;
  let match;
  if (closest($anchor, node => node.type === schema.nodes.p) !== null) {
    return setBlockType(schema.nodes.h, { l: level } as HeadingAttrs)(state, dispatch);
  } else if ((match = closest($anchor, node => node.type === schema.nodes.h)) !== null) {
    if ((match.node.attrs as HeadingAttrs).l === level) {
      return setBlockType(schema.nodes.p)(state, dispatch);
    } else {
      return setBlockType(schema.nodes.h, { l: level } as HeadingAttrs)(state, dispatch);
    }
  }
  return false;
};

export const toggleHeading1 = toggleHeading(1);
export const toggleHeading2 = toggleHeading(2);

export const ux = {
  [UxCommand.DeleteBackward]: escapeFromStart,
  [UxCommand.ToggleHeading1]: toggleHeading1,
  [UxCommand.ToggleHeading2]: toggleHeading2
};