dataTable/src/selection.js

export const createSelectionManager = (container, state) => {
    let activeBounds = null; // { minRow, maxRow, minCol, maxCol }
    let startCell = null; // { row, col }
    let multiSelections = [];

    const isCellSelected = (r, c) => {
        if (activeBounds && r >= activeBounds.minRow && r <= activeBounds.maxRow && c >= activeBounds.minCol && c <= activeBounds.maxCol) return true;
        return multiSelections.some(s => r >= s.minRow && r <= s.maxRow && c >= s.minCol && c <= s.maxCol);
    };

    const applySelectionUI = () => {
        const rowNodes = container.querySelectorAll('.dt-body-row');
        
        let boundMinRow = Infinity, boundMaxRow = -Infinity;
        if (activeBounds) {
            boundMinRow = Math.min(boundMinRow, activeBounds.minRow);
            boundMaxRow = Math.max(boundMaxRow, activeBounds.maxRow);
        }
        multiSelections.forEach(s => {
            boundMinRow = Math.min(boundMinRow, s.minRow);
            boundMaxRow = Math.max(boundMaxRow, s.maxRow);
        });

        const hasSelection = boundMinRow !== Infinity;

        rowNodes.forEach((rowNode, r) => {
            const absoluteRow = r + state._listStartIndex;
            const cellNodes = rowNode.children;
            
            // Fast path: Row completely outside selection
            if (!hasSelection || absoluteRow < boundMinRow || absoluteRow > boundMaxRow) {
                for (let i = 0; i < cellNodes.length; i++) {
                    if (cellNodes[i].classList.contains('dt-cell-selected')) {
                        cellNodes[i].classList.remove('dt-cell-selected');
                    }
                }
                return;
            }

            for (let i = 0; i < cellNodes.length; i++) {
                const isSelected = isCellSelected(absoluteRow, i);
                const hasClass = cellNodes[i].classList.contains('dt-cell-selected');
                if (isSelected && !hasClass) {
                    cellNodes[i].classList.add('dt-cell-selected');
                } else if (!isSelected && hasClass) {
                    cellNodes[i].classList.remove('dt-cell-selected');
                }
            }
        });
    };

    const updateStatus = () => {
        let count = 0;
        if (activeBounds) count += (activeBounds.maxRow - activeBounds.minRow + 1);
        multiSelections.forEach(s => count += (s.maxRow - s.minRow + 1));
        state.selectedRowCount = count;
    };

    const clearAllActive = (keepSelection = false) => {
        if (!keepSelection) {
            activeBounds = null;
            startCell = null;
            multiSelections = [];
            applySelectionUI();
            updateStatus();
        }
    };

    const startSelect = (row, col, e) => {
        const alreadySelected = isCellSelected(row, col);
        if (e.shiftKey && startCell) {
            activeBounds = {
                minRow: Math.min(startCell.row, row),
                maxRow: Math.max(startCell.row, row),
                minCol: Math.min(startCell.col, col),
                maxCol: Math.max(startCell.col, col)
            };
        } else {
            if (!alreadySelected) {
                if (!e.ctrlKey && !e.metaKey) {
                    clearAllActive();
                } else if (activeBounds) {
                    multiSelections.push(activeBounds);
                }
                startCell = { row, col };
                activeBounds = { minRow: row, maxRow: row, minCol: col, maxCol: col };
            }
            state.isSelecting = true;
        }
        applySelectionUI();
        updateStatus();
        container.focus();
    };

    const updateSelect = (row, col) => {
        if (state.isSelecting && startCell) {
            activeBounds = {
                minRow: Math.min(startCell.row, row),
                maxRow: Math.max(startCell.row, row),
                minCol: Math.min(startCell.col, col),
                maxCol: Math.max(startCell.col, col)
            };
            applySelectionUI();
            updateStatus();
        }
    };

    const endSelect = () => { state.isSelecting = false; };

    const getSelectionBounds = () => {
        if (!activeBounds) return null;
        let minRow = activeBounds.minRow, maxRow = activeBounds.maxRow;
        let minCol = activeBounds.minCol, maxCol = activeBounds.maxCol;
        multiSelections.forEach(s => {
            minRow = Math.min(minRow, s.minRow);
            maxRow = Math.max(maxRow, s.maxRow);
            minCol = Math.min(minCol, s.minCol);
            maxCol = Math.max(maxCol, s.maxCol);
        });
        return { minRow, maxRow, minCol, maxCol };
    };

    const deleteSelected = () => {
        const bounds = getSelectionBounds();
        if (!bounds) return;
        
        // This is a naive deletion that removes the bounding box rows entirely.
        // A complete implementation might filter row by row checking multi-selections.
        const rMin = bounds.minRow, rMax = bounds.maxRow;
        const newList = state.list.filter((_, i) => !(i >= rMin && i <= rMax));
        state.list = newList;
        clearAllActive();
    };

    return {
        applySelectionUI,
        clearAllActive,
        startSelect,
        updateSelect,
        endSelect,
        deleteSelected,
        getSelectionBounds
    };
};