@minht11/solid-virtual-container/dist/source/helpers/diff-positions.js

Virtual list/grid for Solid-js.

import { createArray } from './utils';
export const ELEMENT_USED_FOR_FOCUS = 1;
export const diffPositions = (options) => {
    const { total, focusPosition, positionCount, startPosition, prevPositions, prevStartPosition, } = options;
    const prevPositionsCount = prevPositions.length;
    const arePositionsStatic = total <= positionCount;
    if (arePositionsStatic) {
        if (prevPositionsCount === positionCount &&
            prevStartPosition === startPosition) {
            return prevPositions;
        }
        return createArray(0, positionCount);
    }
    const endPosition = startPosition + positionCount;
    const isPositionOutOfBounds = (pos) => pos < startPosition || pos >= endPosition;
    // Focused position must remain static,
    // so add one more position.
    const findExpandedPositionForFocus = () => {
        if (isPositionOutOfBounds(focusPosition)) {
            return focusPosition;
        }
        let newPosition;
        if (endPosition < total) {
            newPosition = endPosition;
            // At the very end of the list there is nowhere to add new postion
            // so instead insert it before startPosition.
        }
        else {
            newPosition = startPosition - 1;
        }
        return newPosition;
    };
    const newPositionsTotalCount = positionCount + ELEMENT_USED_FOR_FOCUS;
    // If arrays are different size diffing won't work.
    // This ussually happens when layout size changes.
    if (prevPositionsCount !== newPositionsTotalCount) {
        const newPositions = createArray(startPosition, positionCount);
        newPositions.push(findExpandedPositionForFocus());
        return newPositions;
    }
    const unusedPositions = [];
    for (let i = 0; i < positionCount; i += 1) {
        const position = startPosition + i;
        if (!prevPositions.includes(position)) {
            unusedPositions.push(position);
        }
    }
    const newAddedPosition = findExpandedPositionForFocus();
    if (!prevPositions.includes(newAddedPosition)) {
        unusedPositions.push(newAddedPosition);
    }
    return prevPositions.map((prevPosition) => {
        if (isPositionOutOfBounds(prevPosition) &&
            prevPosition !== newAddedPosition) {
            return unusedPositions.pop();
        }
        return prevPosition;
    });
};