ckeditor/ckeditor5-list

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src/converters.js

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/**
 * @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
 * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
 */

/**
 * @module list/converters
 */

import {
    generateLiInUl,
    injectViewList,
    mergeViewLists,
    getSiblingListItem,
    positionAfterUiElements
} from './utils';
import TreeWalker from '@ckeditor/ckeditor5-engine/src/model/treewalker';

/**
 * A model-to-view converter for the `listItem` model element insertion.
 *
 * It creates a `<ul><li></li><ul>` (or `<ol>`) view structure out of a `listItem` model element, inserts it at the correct
 * position, and merges the list with surrounding lists (if available).
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:insert
 * @param {module:engine/model/model~Model} model Model instance.
 * @returns {Function} Returns a conversion callback.
 */
export function modelViewInsertion( model ) {
    return ( evt, data, conversionApi ) => {
        const consumable = conversionApi.consumable;

        if ( !consumable.test( data.item, 'insert' ) ||
            !consumable.test( data.item, 'attribute:listType' ) ||
            !consumable.test( data.item, 'attribute:listIndent' )
        ) {
            return;
        }

        consumable.consume( data.item, 'insert' );
        consumable.consume( data.item, 'attribute:listType' );
        consumable.consume( data.item, 'attribute:listIndent' );

        const modelItem = data.item;
        const viewItem = generateLiInUl( modelItem, conversionApi );

        injectViewList( modelItem, viewItem, conversionApi, model );
    };
}

/**
 * A model-to-view converter for the `listItem` model element removal.
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:remove
 * @param {module:engine/model/model~Model} model Model instance.
 * @returns {Function} Returns a conversion callback.
 */
export function modelViewRemove( model ) {
    return ( evt, data, conversionApi ) => {
        const viewStart = conversionApi.mapper.toViewPosition( data.position ).getLastMatchingPosition( value => !value.item.is( 'li' ) );
        const viewItem = viewStart.nodeAfter;
        const viewWriter = conversionApi.writer;

        // 1. Break the container after and before the list item.
        // This will create a view list with one view list item - the one to remove.
        viewWriter.breakContainer( viewWriter.createPositionBefore( viewItem ) );
        viewWriter.breakContainer( viewWriter.createPositionAfter( viewItem ) );

        // 2. Remove the list with the item to remove.
        const viewList = viewItem.parent;
        const viewListPrev = viewList.previousSibling;
        const removeRange = viewWriter.createRangeOn( viewList );
        const removed = viewWriter.remove( removeRange );

        // 3. Merge the whole created by breaking and removing the list.
        if ( viewListPrev && viewListPrev.nextSibling ) {
            mergeViewLists( viewWriter, viewListPrev, viewListPrev.nextSibling );
        }

        // 4. Bring back nested list that was in the removed <li>.
        const modelItem = conversionApi.mapper.toModelElement( viewItem );

        hoistNestedLists( modelItem.getAttribute( 'listIndent' ) + 1, data.position, removeRange.start, viewItem, conversionApi, model );

        // 5. Unbind removed view item and all children.
        for ( const child of viewWriter.createRangeIn( removed ).getItems() ) {
            conversionApi.mapper.unbindViewElement( child );
        }

        evt.stop();
    };
}

/**
 * A model-to-view converter for the `type` attribute change on the `listItem` model element.
 *
 * This change means that the `<li>` element parent changes from `<ul>` to `<ol>` (or vice versa). This is accomplished
 * by breaking view elements and changing their name. The next {@link module:list/converters~modelViewMergeAfterChangeType}
 * converter will attempt to merge split nodes.
 *
 * Splitting this conversion into 2 steps makes it possible to add an additional conversion in the middle.
 * Check {@link module:list/todolistconverters~modelViewChangeType} to see an example of it.
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:attribute
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data Additional information about the change.
 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi Conversion interface.
 */
export function modelViewChangeType( evt, data, conversionApi ) {
    if ( !conversionApi.consumable.consume( data.item, 'attribute:listType' ) ) {
        return;
    }

    const viewItem = conversionApi.mapper.toViewElement( data.item );
    const viewWriter = conversionApi.writer;

    // Break the container after and before the list item.
    // This will create a view list with one view list item -- the one that changed type.
    viewWriter.breakContainer( viewWriter.createPositionBefore( viewItem ) );
    viewWriter.breakContainer( viewWriter.createPositionAfter( viewItem ) );

    // Change name of the view list that holds the changed view item.
    // We cannot just change name property, because that would not render properly.
    const viewList = viewItem.parent;
    const listName = data.attributeNewValue == 'numbered' ? 'ol' : 'ul';

    viewWriter.rename( listName, viewList );
}

/**
 * A model-to-view converter that attempts to merge nodes split by {@link module:list/converters~modelViewChangeType}.
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:attribute
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data Additional information about the change.
 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi Conversion interface.
 */
export function modelViewMergeAfterChangeType( evt, data, conversionApi ) {
    const viewItem = conversionApi.mapper.toViewElement( data.item );
    const viewList = viewItem.parent;
    const viewWriter = conversionApi.writer;

    // Merge the changed view list with other lists, if possible.
    mergeViewLists( viewWriter, viewList, viewList.nextSibling );
    mergeViewLists( viewWriter, viewList.previousSibling, viewList );

    // Consumable insertion of children inside the item. They are already handled by re-building the item in view.
    for ( const child of data.item.getChildren() ) {
        conversionApi.consumable.consume( child, 'insert' );
    }
}

/**
 * A model-to-view converter for the `listIndent` attribute change on the `listItem` model element.
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:attribute
 * @param {module:engine/model/model~Model} model Model instance.
 * @returns {Function} Returns a conversion callback.
 */
export function modelViewChangeIndent( model ) {
    return ( evt, data, conversionApi ) => {
        if ( !conversionApi.consumable.consume( data.item, 'attribute:listIndent' ) ) {
            return;
        }

        const viewItem = conversionApi.mapper.toViewElement( data.item );
        const viewWriter = conversionApi.writer;

        // 1. Break the container after and before the list item.
        // This will create a view list with one view list item -- the one that changed type.
        viewWriter.breakContainer( viewWriter.createPositionBefore( viewItem ) );
        viewWriter.breakContainer( viewWriter.createPositionAfter( viewItem ) );

        // 2. Extract view list with changed view list item and merge "hole" possibly created by breaking and removing elements.
        const viewList = viewItem.parent;
        const viewListPrev = viewList.previousSibling;
        const removeRange = viewWriter.createRangeOn( viewList );
        viewWriter.remove( removeRange );

        if ( viewListPrev && viewListPrev.nextSibling ) {
            mergeViewLists( viewWriter, viewListPrev, viewListPrev.nextSibling );
        }

        // 3. Bring back nested list that was in the removed <li>.
        hoistNestedLists( data.attributeOldValue + 1, data.range.start, removeRange.start, viewItem, conversionApi, model );

        // 4. Inject view list like it is newly inserted.
        injectViewList( data.item, viewItem, conversionApi, model );

        // 5. Consume insertion of children inside the item. They are already handled by re-building the item in view.
        for ( const child of data.item.getChildren() ) {
            conversionApi.consumable.consume( child, 'insert' );
        }
    };
}

/**
 * A special model-to-view converter introduced by the {@link module:list/list~List list feature}. This converter is fired for
 * insert change of every model item, and should be fired before the actual converter. The converter checks whether the inserted
 * model item is a non-`listItem` element. If it is, and it is inserted inside a view list, the converter breaks the
 * list so the model element is inserted to the view parent element corresponding to its model parent element.
 *
 * The converter prevents such situations:
 *
 *        // Model:                        // View:
 *        <listItem>foo</listItem>         <ul>
 *        <listItem>bar</listItem>             <li>foo</li>
 *                                             <li>bar</li>
 *                                         </ul>
 *
 *        // After change:                 // Correct view guaranteed by this converter:
 *        <listItem>foo</listItem>         <ul><li>foo</li></ul><p>xxx</p><ul><li>bar</li></ul>
 *        <paragraph>xxx</paragraph>       // Instead of this wrong view state:
 *        <listItem>bar</listItem>         <ul><li>foo</li><p>xxx</p><li>bar</li></ul>
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:insert
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data Additional information about the change.
 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi Conversion interface.
 */
export function modelViewSplitOnInsert( evt, data, conversionApi ) {
    if ( data.item.name != 'listItem' ) {
        let viewPosition = conversionApi.mapper.toViewPosition( data.range.start );

        const viewWriter = conversionApi.writer;
        const lists = [];

        // Break multiple ULs/OLs if there are.
        //
        // Imagine following list:
        //
        // 1 --------
        //   1.1 --------
        //     1.1.1 --------
        //     1.1.2 --------
        //     1.1.3 --------
        //       1.1.3.1 --------
        //   1.2 --------
        //     1.2.1 --------
        // 2 --------
        //
        // Insert paragraph after item 1.1.1:
        //
        // 1 --------
        //   1.1 --------
        //     1.1.1 --------
        //
        // Lorem ipsum.
        //
        //     1.1.2 --------
        //     1.1.3 --------
        //       1.1.3.1 --------
        //   1.2 --------
        //     1.2.1 --------
        // 2 --------
        //
        // In this case 1.1.2 has to become beginning of a new list.
        // We need to break list before 1.1.2 (obvious), then we need to break list also before 1.2.
        // Then we need to move those broken pieces one after another and merge:
        //
        // 1 --------
        //   1.1 --------
        //     1.1.1 --------
        //
        // Lorem ipsum.
        //
        // 1.1.2 --------
        //   1.1.3 --------
        //     1.1.3.1 --------
        // 1.2 --------
        //   1.2.1 --------
        // 2 --------
        //
        while ( viewPosition.parent.name == 'ul' || viewPosition.parent.name == 'ol' ) {
            viewPosition = viewWriter.breakContainer( viewPosition );

            if ( viewPosition.parent.name != 'li' ) {
                break;
            }

            // Remove lists that are after inserted element.
            // They will be brought back later, below the inserted element.
            const removeStart = viewPosition;
            const removeEnd = viewWriter.createPositionAt( viewPosition.parent, 'end' );

            // Don't remove if there is nothing to remove.
            if ( !removeStart.isEqual( removeEnd ) ) {
                const removed = viewWriter.remove( viewWriter.createRange( removeStart, removeEnd ) );
                lists.push( removed );
            }

            viewPosition = viewWriter.createPositionAfter( viewPosition.parent );
        }

        // Bring back removed lists.
        if ( lists.length > 0 ) {
            for ( let i = 0; i < lists.length; i++ ) {
                const previousList = viewPosition.nodeBefore;
                const insertedRange = viewWriter.insert( viewPosition, lists[ i ] );
                viewPosition = insertedRange.end;

                // Don't merge first list! We want a split in that place (this is why this converter is introduced).
                if ( i > 0 ) {
                    const mergePos = mergeViewLists( viewWriter, previousList, previousList.nextSibling );

                    // If `mergePos` is in `previousList` it means that the lists got merged.
                    // In this case, we need to fix insert position.
                    if ( mergePos && mergePos.parent == previousList ) {
                        viewPosition.offset--;
                    }
                }
            }

            // Merge last inserted list with element after it.
            mergeViewLists( viewWriter, viewPosition.nodeBefore, viewPosition.nodeAfter );
        }
    }
}

/**
 * A special model-to-view converter introduced by the {@link module:list/list~List list feature}. This converter takes care of
 * merging view lists after something is removed or moved from near them.
 *
 * Example:
 *
 *        // Model:                        // View:
 *        <listItem>foo</listItem>         <ul><li>foo</li></ul>
 *        <paragraph>xxx</paragraph>       <p>xxx</p>
 *        <listItem>bar</listItem>         <ul><li>bar</li></ul>
 *
 *        // After change:                 // Correct view guaranteed by this converter:
 *        <listItem>foo</listItem>         <ul>
 *        <listItem>bar</listItem>             <li>foo</li>
 *                                             <li>bar</li>
 *                                         </ul>
 *
 * @see module:engine/conversion/downcastdispatcher~DowncastDispatcher#event:remove
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data Additional information about the change.
 * @param {module:engine/conversion/downcastdispatcher~DowncastConversionApi} conversionApi Conversion interface.
 */
export function modelViewMergeAfter( evt, data, conversionApi ) {
    const viewPosition = conversionApi.mapper.toViewPosition( data.position );
    const viewItemPrev = viewPosition.nodeBefore;
    const viewItemNext = viewPosition.nodeAfter;

    // Merge lists if something (remove, move) was done from inside of list.
    // Merging will be done only if both items are view lists of the same type.
    // The check is done inside the helper function.
    mergeViewLists( conversionApi.writer, viewItemPrev, viewItemNext );
}

/**
 * A view-to-model converter that converts the `<li>` view elements into the `listItem` model elements.
 *
 * To set correct values of the `listType` and `listIndent` attributes the converter:
 * * checks `<li>`'s parent,
 * * stores and increases the `conversionApi.store.indent` value when `<li>`'s sub-items are converted.
 *
 * @see module:engine/conversion/upcastdispatcher~UpcastDispatcher#event:element
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data An object containing conversion input and a placeholder for conversion output and possibly other values.
 * @param {module:engine/conversion/upcastdispatcher~UpcastConversionApi} conversionApi Conversion interface to be used by the callback.
 */
export function viewModelConverter( evt, data, conversionApi ) {
    if ( conversionApi.consumable.consume( data.viewItem, { name: true } ) ) {
        const writer = conversionApi.writer;

        // 1. Create `listItem` model element.
        const listItem = writer.createElement( 'listItem' );

        // 2. Handle `listItem` model element attributes.
        const indent = getIndent( data.viewItem );

        writer.setAttribute( 'listIndent', indent, listItem );

        // Set 'bulleted' as default. If this item is pasted into a context,
        const type = data.viewItem.parent && data.viewItem.parent.name == 'ol' ? 'numbered' : 'bulleted';
        writer.setAttribute( 'listType', type, listItem );

        // Try to find allowed parent for list item.
        const splitResult = conversionApi.splitToAllowedParent( listItem, data.modelCursor );

        // When there is no allowed parent it means that list item cannot be converted at current model position
        // and in any of position ancestors.
        if ( !splitResult ) {
            return;
        }

        writer.insert( listItem, splitResult.position );

        const nextPosition = viewToModelListItemChildrenConverter( listItem, data.viewItem.getChildren(), conversionApi );

        // Result range starts before the first item and ends after the last.
        data.modelRange = writer.createRange( data.modelCursor, nextPosition );

        // When `data.modelCursor` parent had to be split to insert list item...
        if ( splitResult.cursorParent ) {
            // Continue conversion in the split element.
            data.modelCursor = writer.createPositionAt( splitResult.cursorParent, 0 );
        } else {
            // Otherwise continue conversion after the last list item.
            data.modelCursor = data.modelRange.end;
        }
    }
}

/**
 * A view-to-model converter for the `<ul>` and `<ol>` view elements that cleans the input view of garbage.
 * This is mostly to clean whitespaces from between the `<li>` view elements inside the view list element, however, also
 * incorrect data can be cleared if the view was incorrect.
 *
 * @see module:engine/conversion/upcastdispatcher~UpcastDispatcher#event:element
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data An object containing conversion input and a placeholder for conversion output and possibly other values.
 * @param {module:engine/conversion/upcastdispatcher~UpcastConversionApi} conversionApi Conversion interface to be used by the callback.
 */
export function cleanList( evt, data, conversionApi ) {
    if ( conversionApi.consumable.test( data.viewItem, { name: true } ) ) {
        // Caching children because when we start removing them iterating fails.
        const children = Array.from( data.viewItem.getChildren() );

        for ( const child of children ) {
            const isWrongElement = !( child.is( 'li' ) || isList( child ) );

            if ( isWrongElement ) {
                child._remove();
            }
        }
    }
}

/**
 * A view-to-model converter for the `<li>` elements that cleans whitespace formatting from the input view.
 *
 * @see module:engine/conversion/upcastdispatcher~UpcastDispatcher#event:element
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Object} data An object containing conversion input and a placeholder for conversion output and possibly other values.
 * @param {module:engine/conversion/upcastdispatcher~UpcastConversionApi} conversionApi Conversion interface to be used by the callback.
 */
export function cleanListItem( evt, data, conversionApi ) {
    if ( conversionApi.consumable.test( data.viewItem, { name: true } ) ) {
        if ( data.viewItem.childCount === 0 ) {
            return;
        }

        const children = [ ...data.viewItem.getChildren() ];

        let foundList = false;
        let firstNode = true;

        for ( const child of children ) {
            if ( foundList && !isList( child ) ) {
                child._remove();
            }

            if ( child.is( 'text' ) ) {
                // If this is the first node and it's a text node, left-trim it.
                if ( firstNode ) {
                    child._data = child.data.replace( /^\s+/, '' );
                }

                // If this is the last text node before <ul> or <ol>, right-trim it.
                if ( !child.nextSibling || isList( child.nextSibling ) ) {
                    child._data = child.data.replace( /\s+$/, '' );
                }
            } else if ( isList( child ) ) {
                // If this is a <ul> or <ol>, do not process it, just mark that we already visited list element.
                foundList = true;
            }

            firstNode = false;
        }
    }
}

/**
 * Returns a callback for model position to view position mapping for {@link module:engine/conversion/mapper~Mapper}. The callback fixes
 * positions between the `listItem` elements that would be incorrectly mapped because of how list items are represented in the model
 * and in the view.
 *
 * @see module:engine/conversion/mapper~Mapper#event:modelToViewPosition
 * @param {module:engine/view/view~View} view A view instance.
 * @returns {Function}
 */
export function modelToViewPosition( view ) {
    return ( evt, data ) => {
        if ( data.isPhantom ) {
            return;
        }

        const modelItem = data.modelPosition.nodeBefore;

        if ( modelItem && modelItem.is( 'listItem' ) ) {
            const viewItem = data.mapper.toViewElement( modelItem );
            const topmostViewList = viewItem.getAncestors().find( isList );
            const walker = view.createPositionAt( viewItem, 0 ).getWalker();

            for ( const value of walker ) {
                if ( value.type == 'elementStart' && value.item.is( 'li' ) ) {
                    data.viewPosition = value.previousPosition;

                    break;
                } else if ( value.type == 'elementEnd' && value.item == topmostViewList ) {
                    data.viewPosition = value.nextPosition;

                    break;
                }
            }
        }
    };
}

/**
 * The callback for view position to model position mapping for {@link module:engine/conversion/mapper~Mapper}. The callback fixes
 * positions between the `<li>` elements that would be incorrectly mapped because of how list items are represented in the model
 * and in the view.
 *
 * @see module:engine/conversion/mapper~Mapper#event:viewToModelPosition
 * @param {module:engine/model/model~Model} model Model instance.
 * @returns {Function} Returns a conversion callback.
 */
export function viewToModelPosition( model ) {
    return ( evt, data ) => {
        const viewPos = data.viewPosition;
        const viewParent = viewPos.parent;
        const mapper = data.mapper;

        if ( viewParent.name == 'ul' || viewParent.name == 'ol' ) {
            // Position is directly in <ul> or <ol>.
            if ( !viewPos.isAtEnd ) {
                // If position is not at the end, it must be before <li>.
                // Get that <li>, map it to `listItem` and set model position before that `listItem`.
                const modelNode = mapper.toModelElement( viewPos.nodeAfter );

                data.modelPosition = model.createPositionBefore( modelNode );
            } else {
                // Position is at the end of <ul> or <ol>, so there is no <li> after it to be mapped.
                // There is <li> before the position, but we cannot just map it to `listItem` and set model position after it,
                // because that <li> may contain nested items.
                // We will check "model length" of that <li>, in other words - how many `listItem`s are in that <li>.
                const modelNode = mapper.toModelElement( viewPos.nodeBefore );
                const modelLength = mapper.getModelLength( viewPos.nodeBefore );

                // Then we get model position before mapped `listItem` and shift it accordingly.
                data.modelPosition = model.createPositionBefore( modelNode ).getShiftedBy( modelLength );
            }

            evt.stop();
        } else if (
            viewParent.name == 'li' &&
            viewPos.nodeBefore &&
            ( viewPos.nodeBefore.name == 'ul' || viewPos.nodeBefore.name == 'ol' )
        ) {
            // In most cases when view position is in <li> it is in text and this is a correct position.
            // However, if position is after <ul> or <ol> we have to fix it -- because in model <ul>/<ol> are not in the `listItem`.
            const modelNode = mapper.toModelElement( viewParent );

            // Check all <ul>s and <ol>s that are in the <li> but before mapped position.
            // Get model length of those elements and then add it to the offset of `listItem` mapped to the original <li>.
            let modelLength = 1; // Starts from 1 because the original <li> has to be counted in too.
            let viewList = viewPos.nodeBefore;

            while ( viewList && isList( viewList ) ) {
                modelLength += mapper.getModelLength( viewList );

                viewList = viewList.previousSibling;
            }

            data.modelPosition = model.createPositionBefore( modelNode ).getShiftedBy( modelLength );

            evt.stop();
        }
    };
}

/**
 * Post-fixer that reacts to changes on document and fixes incorrect model states.
 *
 * In the example below, there is a correct list structure.
 * Then the middle element is removed so the list structure will become incorrect:
 *
 *        <listItem listType="bulleted" listIndent=0>Item 1</listItem>
 *        <listItem listType="bulleted" listIndent=1>Item 2</listItem>   <--- this is removed.
 *        <listItem listType="bulleted" listIndent=2>Item 3</listItem>
 *
 * The list structure after the middle element is removed:
 *
 *         <listItem listType="bulleted" listIndent=0>Item 1</listItem>
 *        <listItem listType="bulleted" listIndent=2>Item 3</listItem>
 *
 * Should become:
 *
 *        <listItem listType="bulleted" listIndent=0>Item 1</listItem>
 *        <listItem listType="bulleted" listIndent=1>Item 3</listItem>   <--- note that indent got post-fixed.
 *
 * @param {module:engine/model/model~Model} model The data model.
 * @param {module:engine/model/writer~Writer} writer The writer to do changes with.
 * @returns {Boolean} `true` if any change has been applied, `false` otherwise.
 */
export function modelChangePostFixer( model, writer ) {
    const changes = model.document.differ.getChanges();
    const itemToListHead = new Map();

    let applied = false;

    for ( const entry of changes ) {
        if ( entry.type == 'insert' && entry.name == 'listItem' ) {
            _addListToFix( entry.position );
        } else if ( entry.type == 'insert' && entry.name != 'listItem' ) {
            if ( entry.name != '$text' ) {
                // In case of renamed element.
                const item = entry.position.nodeAfter;

                if ( item.hasAttribute( 'listIndent' ) ) {
                    writer.removeAttribute( 'listIndent', item );

                    applied = true;
                }

                if ( item.hasAttribute( 'listType' ) ) {
                    writer.removeAttribute( 'listType', item );

                    applied = true;
                }

                for ( const innerItem of Array.from( model.createRangeIn( item ) ).filter( e => e.item.is( 'listItem' ) ) ) {
                    _addListToFix( innerItem.previousPosition );
                }
            }

            const posAfter = entry.position.getShiftedBy( entry.length );

            _addListToFix( posAfter );
        } else if ( entry.type == 'remove' && entry.name == 'listItem' ) {
            _addListToFix( entry.position );
        } else if ( entry.type == 'attribute' && entry.attributeKey == 'listIndent' ) {
            _addListToFix( entry.range.start );
        } else if ( entry.type == 'attribute' && entry.attributeKey == 'listType' ) {
            _addListToFix( entry.range.start );
        }
    }

    for ( const listHead of itemToListHead.values() ) {
        _fixListIndents( listHead );
        _fixListTypes( listHead );
    }

    return applied;

    function _addListToFix( position ) {
        const previousNode = position.nodeBefore;

        if ( !previousNode || !previousNode.is( 'listItem' ) ) {
            const item = position.nodeAfter;

            if ( item && item.is( 'listItem' ) ) {
                itemToListHead.set( item, item );
            }
        } else {
            let listHead = previousNode;

            if ( itemToListHead.has( listHead ) ) {
                return;
            }

            for (
                // Cache previousSibling and reuse for performance reasons. See #6581.
                let previousSibling = listHead.previousSibling;
                previousSibling && previousSibling.is( 'listItem' );
                previousSibling = listHead.previousSibling
            ) {
                listHead = previousSibling;

                if ( itemToListHead.has( listHead ) ) {
                    return;
                }
            }

            itemToListHead.set( previousNode, listHead );
        }
    }

    function _fixListIndents( item ) {
        let maxIndent = 0;
        let fixBy = null;

        while ( item && item.is( 'listItem' ) ) {
            const itemIndent = item.getAttribute( 'listIndent' );

            if ( itemIndent > maxIndent ) {
                let newIndent;

                if ( fixBy === null ) {
                    fixBy = itemIndent - maxIndent;
                    newIndent = maxIndent;
                } else {
                    if ( fixBy > itemIndent ) {
                        fixBy = itemIndent;
                    }

                    newIndent = itemIndent - fixBy;
                }

                writer.setAttribute( 'listIndent', newIndent, item );

                applied = true;
            } else {
                fixBy = null;
                maxIndent = item.getAttribute( 'listIndent' ) + 1;
            }

            item = item.nextSibling;
        }
    }

    function _fixListTypes( item ) {
        let typesStack = [];
        let prev = null;

        while ( item && item.is( 'listItem' ) ) {
            const itemIndent = item.getAttribute( 'listIndent' );

            if ( prev && prev.getAttribute( 'listIndent' ) > itemIndent ) {
                typesStack = typesStack.slice( 0, itemIndent + 1 );
            }

            if ( itemIndent != 0 ) {
                if ( typesStack[ itemIndent ] ) {
                    const type = typesStack[ itemIndent ];

                    if ( item.getAttribute( 'listType' ) != type ) {
                        writer.setAttribute( 'listType', type, item );

                        applied = true;
                    }
                } else {
                    typesStack[ itemIndent ] = item.getAttribute( 'listType' );
                }
            }

            prev = item;
            item = item.nextSibling;
        }
    }
}

/**
 * A fixer for pasted content that includes list items.
 *
 * It fixes indentation of pasted list items so the pasted items match correctly to the context they are pasted into.
 *
 * Example:
 *
 *        <listItem listType="bulleted" listIndent=0>A</listItem>
 *        <listItem listType="bulleted" listIndent=1>B^</listItem>
 *        // At ^ paste:  <listItem listType="bulleted" listIndent=4>X</listItem>
 *        //              <listItem listType="bulleted" listIndent=5>Y</listItem>
 *        <listItem listType="bulleted" listIndent=2>C</listItem>
 *
 * Should become:
 *
 *        <listItem listType="bulleted" listIndent=0>A</listItem>
 *        <listItem listType="bulleted" listIndent=1>BX</listItem>
 *        <listItem listType="bulleted" listIndent=2>Y/listItem>
 *        <listItem listType="bulleted" listIndent=2>C</listItem>
 *
 * @param {module:utils/eventinfo~EventInfo} evt An object containing information about the fired event.
 * @param {Array} args Arguments of {@link module:engine/model/model~Model#insertContent}.
 */
export function modelIndentPasteFixer( evt, [ content, selectable ] ) {
    // Check whether inserted content starts from a `listItem`. If it does not, it means that there are some other
    // elements before it and there is no need to fix indents, because even if we insert that content into a list,
    // that list will be broken.
    // Note: we also need to handle singular elements because inserting item with indent 0 into 0,1,[],2
    // would create incorrect model.
    let item = content.is( 'documentFragment' ) ? content.getChild( 0 ) : content;

    let selection;

    if ( !selectable ) {
        selection = this.document.selection;
    } else {
        selection = this.createSelection( selectable );
    }

    if ( item && item.is( 'listItem' ) ) {
        // Get a reference list item. Inserted list items will be fixed according to that item.
        const pos = selection.getFirstPosition();
        let refItem = null;

        if ( pos.parent.is( 'listItem' ) ) {
            refItem = pos.parent;
        } else if ( pos.nodeBefore && pos.nodeBefore.is( 'listItem' ) ) {
            refItem = pos.nodeBefore;
        }

        // If there is `refItem` it means that we do insert list items into an existing list.
        if ( refItem ) {
            // First list item in `data` has indent equal to 0 (it is a first list item). It should have indent equal
            // to the indent of reference item. We have to fix the first item and all of it's children and following siblings.
            // Indent of all those items has to be adjusted to reference item.
            const indentChange = refItem.getAttribute( 'listIndent' );

            // Fix only if there is anything to fix.
            if ( indentChange > 0 ) {
                // Adjust indent of all "first" list items in inserted data.
                while ( item && item.is( 'listItem' ) ) {
                    item._setAttribute( 'listIndent', item.getAttribute( 'listIndent' ) + indentChange );

                    item = item.nextSibling;
                }
            }
        }
    }
}

// Helper function that converts children of a given `<li>` view element into corresponding model elements.
// The function maintains proper order of elements if model `listItem` is split during the conversion
// due to block children conversion.
//
// @param {module:engine/model/element~Element} listItemModel List item model element to which converted children will be inserted.
// @param {Iterable.<module:engine/view/node~Node>} viewChildren View elements which will be converted.
// @param {module:engine/conversion/upcastdispatcher~UpcastConversionApi} conversionApi Conversion interface to be used by the callback.
// @returns {module:engine/model/position~Position} Position on which next elements should be inserted after children conversion.
function viewToModelListItemChildrenConverter( listItemModel, viewChildren, conversionApi ) {
    const { writer, schema } = conversionApi;

    // A position after the last inserted `listItem`.
    let nextPosition = writer.createPositionAfter( listItemModel );

    // Check all children of the converted `<li>`. At this point we assume there are no "whitespace" view text nodes
    // in view list, between view list items. This should be handled by `<ul>` and `<ol>` converters.
    for ( const child of viewChildren ) {
        if ( child.name == 'ul' || child.name == 'ol' ) {
            // If the children is a list, we will insert its conversion result after currently handled `listItem`.
            // Then, next insertion position will be set after all the new list items (and maybe other elements if
            // something split list item).
            //
            // If this is a list, we expect that some `listItem`s and possibly other blocks will be inserted, however `.modelCursor`
            // should be set after last `listItem` (or block). This is why it feels safe to use it as `nextPosition`
            nextPosition = conversionApi.convertItem( child, nextPosition ).modelCursor;
        } else {
            // If this is not a list, try inserting content at the end of the currently handled `listItem`.
            const result = conversionApi.convertItem( child, writer.createPositionAt( listItemModel, 'end' ) );

            // It may end up that the current `listItem` becomes split (if that content cannot be inside `listItem`). For example:
            //
            // <li><p>Foo</p></li>
            //
            // will be converted to:
            //
            // <listItem></listItem><paragraph>Foo</paragraph><listItem></listItem>
            //
            const convertedChild = result.modelRange.start.nodeAfter;
            const wasSplit = convertedChild && convertedChild.is( 'element' ) && !schema.checkChild( listItemModel, convertedChild.name );

            if ( wasSplit ) {
                // As `lastListItem` got split, we need to update it to the second part of the split `listItem` element.
                //
                // `modelCursor` should be set to a position where the conversion should continue. There are multiple possible scenarios
                // that may happen. Usually, `modelCursor` (marked as `#` below) would point to the second list item after conversion:
                //
                //        `<li><p>Foo</p></li>` -> `<listItem></listItem><paragraph>Foo</paragraph><listItem>#</listItem>`
                //
                // However, in some cases, like auto-paragraphing, the position is placed at the end of the block element:
                //
                //        `<li><div>Foo</div></li>` -> `<listItem></listItem><paragraph>Foo#</paragraph><listItem></listItem>`
                //
                // or after an element if another element broken auto-paragraphed element:
                //
                //        `<li><div><h2>Foo</h2></div></li>` -> `<listItem></listItem><heading1>Foo</heading1>#<listItem></listItem>`
                //
                // We need to check for such cases and use proper list item and position based on it.
                //
                if ( result.modelCursor.parent.is( 'listItem' ) ) {
                    // (1).
                    listItemModel = result.modelCursor.parent;
                } else {
                    // (2), (3).
                    listItemModel = findNextListItem( result.modelCursor );
                }

                nextPosition = writer.createPositionAfter( listItemModel );
            }
        }
    }

    return nextPosition;
}

// Helper function that seeks for a next list item starting from given `startPosition`.
function findNextListItem( startPosition ) {
    const treeWalker = new TreeWalker( { startPosition } );

    let value;

    do {
        value = treeWalker.next();
    } while ( !value.value.item.is( 'listItem' ) );

    return value.value.item;
}

// Helper function that takes all children of given `viewRemovedItem` and moves them in a correct place, according
// to other given parameters.
function hoistNestedLists( nextIndent, modelRemoveStartPosition, viewRemoveStartPosition, viewRemovedItem, conversionApi, model ) {
    // Find correct previous model list item element.
    // The element has to have either same or smaller indent than given reference indent.
    // This will be the model element which will get nested items (if it has smaller indent) or sibling items (if it has same indent).
    // Keep in mind that such element might not be found, if removed item was the first item.
    const prevModelItem = getSiblingListItem( modelRemoveStartPosition.nodeBefore, {
        sameIndent: true,
        smallerIndent: true,
        listIndent: nextIndent,
        foo: 'b'
    } );

    const mapper = conversionApi.mapper;
    const viewWriter = conversionApi.writer;

    // Indent of found element or `null` if the element has not been found.
    const prevIndent = prevModelItem ? prevModelItem.getAttribute( 'listIndent' ) : null;

    let insertPosition;

    if ( !prevModelItem ) {
        // If element has not been found, simply insert lists at the position where the removed item was:
        //
        // Lorem ipsum.
        // 1 --------           <--- this is removed, no previous list item, put nested items in place of removed item.
        //   1.1 --------       <--- this is reference indent.
        //     1.1.1 --------
        //     1.1.2 --------
        //   1.2 --------
        //
        // Becomes:
        //
        // Lorem ipsum.
        // 1.1 --------
        //   1.1.1 --------
        //   1.1.2 --------
        // 1.2 --------
        insertPosition = viewRemoveStartPosition;
    } else if ( prevIndent == nextIndent ) {
        // If element has been found and has same indent as reference indent it means that nested items should
        // become siblings of found element:
        //
        // 1 --------
        //   1.1 --------
        //   1.2 --------       <--- this is `prevModelItem`.
        // 2 --------           <--- this is removed, previous list item has indent same as reference indent.
        //   2.1 --------       <--- this is reference indent, this and 2.2 should become siblings of 1.2.
        //   2.2 --------
        //
        // Becomes:
        //
        // 1 --------
        //   1.1 --------
        //   1.2 --------
        //   2.1 --------
        //   2.2 --------
        const prevViewList = mapper.toViewElement( prevModelItem ).parent;
        insertPosition = viewWriter.createPositionAfter( prevViewList );
    } else {
        // If element has been found and has smaller indent as reference indent it means that nested items
        // should become nested items of found item:
        //
        // 1 --------           <--- this is `prevModelItem`.
        //   1.1 --------       <--- this is removed, previous list item has indent smaller than reference indent.
        //     1.1.1 --------   <--- this is reference indent, this and 1.1.1 should become nested items of 1.
        //     1.1.2 --------
        //   1.2 --------
        //
        // Becomes:
        //
        // 1 --------
        //   1.1.1 --------
        //   1.1.2 --------
        //   1.2 --------
        //
        // Note: in this case 1.1.1 have indent 2 while 1 have indent 0. In model that should not be possible,
        // because following item may have indent bigger only by one. But this is fixed by postfixer.
        const modelPosition = model.createPositionAt( prevModelItem, 'end' );
        insertPosition = mapper.toViewPosition( modelPosition );
    }

    insertPosition = positionAfterUiElements( insertPosition );

    // Handle multiple lists. This happens if list item has nested numbered and bulleted lists. Following lists
    // are inserted after the first list (no need to recalculate insertion position for them).
    for ( const child of [ ...viewRemovedItem.getChildren() ] ) {
        if ( isList( child ) ) {
            insertPosition = viewWriter.move( viewWriter.createRangeOn( child ), insertPosition ).end;

            mergeViewLists( viewWriter, child, child.nextSibling );
            mergeViewLists( viewWriter, child.previousSibling, child );
        }
    }
}

// Checks if view element is a list type (ul or ol).
//
// @param {module:engine/view/element~Element} viewElement
// @returns {Boolean}
function isList( viewElement ) {
    return viewElement.is( 'ol' ) || viewElement.is( 'ul' );
}

// Calculates the indent value for a list item. Handles HTML compliant and non-compliant lists.
//
// Also, fixes non HTML compliant lists indents:
//
//        before:                                     fixed list:
//        OL                                          OL
//        |-> LI (parent LIs: 0)                      |-> LI     (indent: 0)
//            |-> OL                                  |-> OL
//                |-> OL                                  |
//                |   |-> OL                              |
//                |       |-> OL                          |
//                |           |-> LI (parent LIs: 1)      |-> LI (indent: 1)
//                |-> LI (parent LIs: 1)                  |-> LI (indent: 1)
//
//        before:                                     fixed list:
//        OL                                          OL
//        |-> OL                                      |
//            |-> OL                                  |
//                 |-> OL                             |
//                     |-> LI (parent LIs: 0)         |-> LI        (indent: 0)
//
//        before:                                     fixed list:
//        OL                                          OL
//        |-> LI (parent LIs: 0)                      |-> LI         (indent: 0)
//        |-> OL                                          |-> OL
//            |-> LI (parent LIs: 0)                          |-> LI (indent: 1)
//
// @param {module:engine/view/element~Element} listItem
// @param {Object} conversionStore
// @returns {Number}
function getIndent( listItem ) {
    let indent = 0;

    let parent = listItem.parent;

    while ( parent ) {
        // Each LI in the tree will result in an increased indent for HTML compliant lists.
        if ( parent.is( 'li' ) ) {
            indent++;
        } else {
            // If however the list is nested in other list we should check previous sibling of any of the list elements...
            const previousSibling = parent.previousSibling;

            // ...because the we might need increase its indent:
            //        before:                           fixed list:
            //        OL                                OL
            //        |-> LI (parent LIs: 0)            |-> LI         (indent: 0)
            //        |-> OL                                |-> OL
            //            |-> LI (parent LIs: 0)                |-> LI (indent: 1)
            if ( previousSibling && previousSibling.is( 'li' ) ) {
                indent++;
            }
        }

        parent = parent.parent;
    }

    return indent;
}