import {
    EditorState,
    Modifier,
    CharacterMetadata,
    SelectionState,
    DraftHandleValue,
} from 'draft-js';
import {List, OrderedSet} from 'immutable';
import {uniq} from 'lodash';

import {getDraftCharacterListForSelection} from './getDraftCharacterListForSelection';
import {resizeDraftSelection} from './resizeDraftSelection';
import {styleNameBelongsToHighlight} from './highlights';
import {isSelectionAtEndOfBlock} from './selectionPositionInBlock';

/**
 * Returns the characters before and after the cursor.
 *   If it fails resizing the selection to the right, it will push a character with an empty style on the left.
 *   If it fails resizing the selection to the left, it will also push a character with an empty style on the right.
 */
function getRelevantCharactersForCollapsedSelection(
    editorState: EditorState,
    collapsedSelection: SelectionState,
): List<CharacterMetadata> {
    let characters = List<CharacterMetadata>();
    const selectionAtTheStartOfTheLine =
        editorState.getSelection().getStartOffset() === 0;
    const selectionAtTheEndOfTheBlock = isSelectionAtEndOfBlock(editorState);
    const resizeLeft = selectionAtTheStartOfTheLine ? 2 : 1; // SDESK-2861
    const resizeRight = selectionAtTheEndOfTheBlock ? 2 : 1; // SDESK-4335
    const resizedSelection = resizeDraftSelection(
        resizeLeft,
        resizeRight,
        collapsedSelection,
        editorState,
        false,
    );
    const resizeLeftFailed =
        collapsedSelection.getStartOffset() ===
        resizedSelection.getStartOffset();
    const resizeRightFailed =
        collapsedSelection.getEndOffset() === resizedSelection.getEndOffset();

    if (resizeLeftFailed === true) {
        characters = characters.push(CharacterMetadata.create());
    }

    characters = characters.merge(
        getDraftCharacterListForSelection(editorState, resizedSelection),
    );

    if (resizeRightFailed === true) {
        characters = characters.push(CharacterMetadata.create());
    }

    return characters;
}

/**
 * @ngdoc method
 * @name handleBeforeInputHighlights
 * @description prevents inheriting of highlight styles
 */
export function handleBeforeInputHighlights(
    onChange,
    chars: string,
    editorState: EditorState,
): DraftHandleValue {
    // see handleBeforeInputHighlights.spec.gif

    const selection = editorState.getSelection();
    const characterList = selection.isCollapsed()
        ? getRelevantCharactersForCollapsedSelection(editorState, selection)
        : getDraftCharacterListForSelection(editorState, selection);
    const characterStyles = characterList
        .map((character) => character.getStyle())
        .toJS();
    const allHighlightStyles = uniq(
        characterStyles.reduce((a, b) => a.concat(b)),
    ).filter(styleNameBelongsToHighlight);

    if (allHighlightStyles.length < 1) {
        return 'not-handled';
    }

    const commonHighlightStyles = allHighlightStyles.filter((styleName) =>
        characterStyles.every((stylesAtPosition) =>
            stylesAtPosition.includes(styleName),
        ),
    );

    const nextInlineStyles = OrderedSet<string>(
        editorState
            .getCurrentInlineStyle()
            .filter(
                (styleName) => styleNameBelongsToHighlight(styleName) === false,
            )
            .concat(commonHighlightStyles),
    );
    const nextContentState = Modifier.replaceText(
        editorState.getCurrentContent(),
        editorState.getSelection(),
        chars,
        nextInlineStyles,
    );
    const nextEditorState = EditorState.push(
        editorState,
        nextContentState,
        'insert-characters',
    );

    onChange(nextEditorState);

    return 'handled';
}