function setDraftEditorSelection()

in src/component/selection/setDraftEditorSelection.js [113:233]
95 lines of code
14 McCabe index (conditional complexity)

function setDraftEditorSelection(
  selectionState: SelectionState,
  node: Node,
  blockKey: string,
  nodeStart: number,
  nodeEnd: number,
): void {
  // It's possible that the editor has been removed from the DOM but
  // our selection code doesn't know it yet. Forcing selection in
  // this case may lead to errors, so just bail now.
  const documentObject = getCorrectDocumentFromNode(node);
  if (!containsNode(documentObject.documentElement, node)) {
    return;
  }

  const selection: SelectionObject = documentObject.defaultView.getSelection();
  let anchorKey = selectionState.getAnchorKey();
  let anchorOffset = selectionState.getAnchorOffset();
  let focusKey = selectionState.getFocusKey();
  let focusOffset = selectionState.getFocusOffset();
  let isBackward = selectionState.getIsBackward();

  // IE doesn't support backward selection. Swap key/offset pairs.
  if (!selection.extend && isBackward) {
    const tempKey = anchorKey;
    const tempOffset = anchorOffset;
    anchorKey = focusKey;
    anchorOffset = focusOffset;
    focusKey = tempKey;
    focusOffset = tempOffset;
    isBackward = false;
  }

  const hasAnchor =
    anchorKey === blockKey &&
    nodeStart <= anchorOffset &&
    nodeEnd >= anchorOffset;

  const hasFocus =
    focusKey === blockKey && nodeStart <= focusOffset && nodeEnd >= focusOffset;

  // If the selection is entirely bound within this node, set the selection
  // and be done.
  if (hasAnchor && hasFocus) {
    selection.removeAllRanges();
    addPointToSelection(
      selection,
      node,
      anchorOffset - nodeStart,
      selectionState,
    );
    addFocusToSelection(
      selection,
      node,
      focusOffset - nodeStart,
      selectionState,
    );
    return;
  }

  if (!isBackward) {
    // If the anchor is within this node, set the range start.
    if (hasAnchor) {
      selection.removeAllRanges();
      addPointToSelection(
        selection,
        node,
        anchorOffset - nodeStart,
        selectionState,
      );
    }

    // If the focus is within this node, we can assume that we have
    // already set the appropriate start range on the selection, and
    // can simply extend the selection.
    if (hasFocus) {
      addFocusToSelection(
        selection,
        node,
        focusOffset - nodeStart,
        selectionState,
      );
    }
  } else {
    // If this node has the focus, set the selection range to be a
    // collapsed range beginning here. Later, when we encounter the anchor,
    // we'll use this information to extend the selection.
    if (hasFocus) {
      selection.removeAllRanges();
      addPointToSelection(
        selection,
        node,
        focusOffset - nodeStart,
        selectionState,
      );
    }

    // If this node has the anchor, we may assume that the correct
    // focus information is already stored on the selection object.
    // We keep track of it, reset the selection range, and extend it
    // back to the focus point.
    if (hasAnchor) {
      const storedFocusNode = selection.focusNode;
      const storedFocusOffset = selection.focusOffset;

      selection.removeAllRanges();
      addPointToSelection(
        selection,
        node,
        anchorOffset - nodeStart,
        selectionState,
      );
      addFocusToSelection(
        selection,
        storedFocusNode,
        storedFocusOffset,
        selectionState,
      );
    }
  }
}