asciitorium/dist/core/ScrollableViewport.js

an ASCII CLUI framework

export class ScrollableViewport {
    calculateScrollWindow(content) {
        const { items, totalCount, maxVisible, focusedIndex } = content;
        // Calculate the starting index to keep focused item centered when possible
        const startIdx = Math.max(0, Math.min(focusedIndex - Math.floor(maxVisible / 2), Math.max(0, totalCount - maxVisible)));
        const visibleItems = items.slice(startIdx, startIdx + maxVisible);
        return {
            startIdx,
            visibleItems,
            showUpArrow: startIdx > 0,
            showDownArrow: startIdx + maxVisible < totalCount
        };
    }
    handleScrollEvent(event, currentFocusedIndex, totalCount) {
        let newFocusedIndex = currentFocusedIndex;
        if ((event === 'ArrowUp') && currentFocusedIndex > 0) {
            newFocusedIndex = currentFocusedIndex - 1;
        }
        else if ((event === 'ArrowDown') &&
            currentFocusedIndex < totalCount - 1) {
            newFocusedIndex = currentFocusedIndex + 1;
        }
        return newFocusedIndex;
    }
    drawScrollIndicators(buffer, width, height, borderPad, showUpArrow, showDownArrow) {
        // Scroll up indicator
        if (showUpArrow) {
            const y = borderPad;
            const x = width - 2;
            if (y >= 0 && y < height && x >= 0 && x < width) {
                buffer[y][x] = '↑';
            }
        }
        // Scroll down indicator
        if (showDownArrow) {
            const y = height - 1 - borderPad;
            const x = width - 2;
            if (y >= 0 && y < height && x >= 0 && x < width) {
                buffer[y][x] = '↓';
            }
        }
    }
}