import { EditorState } from 'draft-js';
import { Map } from 'immutable';
import decodeOffsetKey from './decodeOffsetKey';

interface TriggerForMentionResult {
  activeOffsetKey: string;
  activeTrigger: string;
}

function filterUndefineds(value: unknown | undefined): boolean {
  return value !== undefined;
}

export default function getTriggerForMention(
  editorState: EditorState,
  searches: Map<string, string>,
  mentionTriggers: string[]
): TriggerForMentionResult | null {
  // get the current selection
  const selection = editorState.getSelection();
  const anchorKey = selection.getAnchorKey();
  const anchorOffset = selection.getAnchorOffset();
  // the list should not be visible if a range is selected or the editor has no focus
  if (!selection.isCollapsed() || !selection.getHasFocus()) {
    return null;
  }

  // identify the start & end positon of each search-text
  const offsetDetails = searches.map((offsetKey) =>
    decodeOffsetKey(offsetKey!)
  );

  // a leave can be empty when it is removed due event.g. using backspace
  // do not check leaves, use full decorated portal text
  const leaves = offsetDetails
    .filter((offsetDetail) => offsetDetail!.blockKey === anchorKey)
    .map((offsetDetail) =>
      editorState
        .getBlockTree(offsetDetail!.blockKey)
        .getIn([offsetDetail!.decoratorKey])
    );

  // if all leaves are undefined the popover should be removed
  if (leaves.every((leave) => leave === undefined)) {
    return null;
  }
  // Checks that the cursor is after the @ character but still somewhere in
  // the word (search term). Setting it to allow the cursor to be left of
  // the @ causes troubles due selection confusion.
  const blockText = editorState
    .getCurrentContent()
    .getBlockForKey(anchorKey)
    .getText();
  const triggerForSelectionInsideWord = leaves
    .filter(filterUndefineds)
    .map(
      ({ start, end }) =>
        mentionTriggers
          .map((trigger) =>
            // @ is the first character
            (start === 0 &&
              anchorOffset >= start + trigger.length && //should not trigger if the cursor is before the trigger
              blockText.substr(0, trigger.length) === trigger &&
              anchorOffset <= end) ||
            // @ is in the text or at the end, multi triggers
            (mentionTriggers.length > 1 &&
              anchorOffset >= start + trigger.length &&
              (blockText.substr(start + 1, trigger.length) === trigger ||
                blockText.substr(start, trigger.length) === trigger) &&
              anchorOffset <= end) ||
            // @ is in the text or at the end, single trigger
            (mentionTriggers.length === 1 &&
              anchorOffset >= start + trigger.length &&
              anchorOffset <= end)
              ? trigger
              : undefined
          )
          .filter(filterUndefineds)[0]
    )
    .filter(filterUndefineds);

  if (triggerForSelectionInsideWord.isEmpty()) {
    return null;
  }

  const [
    activeOffsetKey,
    activeTrigger,
  ] = triggerForSelectionInsideWord.entrySeq().first();

  return {
    activeOffsetKey,
    activeTrigger,
  };
}