projects/swimlane/ngx-datatable/src/lib/utils/row-height-cache.ts
/**
* This object contains the cache of the various row heights that are present inside
* the data table. Its based on Fenwick tree data structure that helps with
* querying sums that have time complexity of log n.
*
* Fenwick Tree Credits: http://petr-mitrichev.blogspot.com/2013/05/fenwick-tree-range-updates.html
* https://github.com/mikolalysenko/fenwick-tree
*
*/
export class RowHeightCache {
/**
* Tree Array stores the cumulative information of the row heights to perform efficient
* range queries and updates. Currently the tree is initialized to the base row
* height instead of the detail row height.
*/
private treeArray: number[] = [];
/**
* Clear the Tree array.
*/
clearCache(): void {
this.treeArray = [];
}
/**
* Initialize the Fenwick tree with row Heights.
*
* @param rows The array of rows which contain the expanded status.
* @param rowHeight The row height.
* @param detailRowHeight The detail row height.
*/
initCache(details: any): void {
const { rows, rowHeight, detailRowHeight, externalVirtual, rowCount, rowIndexes, rowExpansions } = details;
const isFn = typeof rowHeight === 'function';
const isDetailFn = typeof detailRowHeight === 'function';
if (!isFn && isNaN(rowHeight)) {
throw new Error(`Row Height cache initialization failed. Please ensure that 'rowHeight' is a
valid number or function value: (${rowHeight}) when 'scrollbarV' is enabled.`);
}
// Add this additional guard in case detailRowHeight is set to 'auto' as it wont work.
if (!isDetailFn && isNaN(detailRowHeight)) {
throw new Error(`Row Height cache initialization failed. Please ensure that 'detailRowHeight' is a
valid number or function value: (${detailRowHeight}) when 'scrollbarV' is enabled.`);
}
const n = externalVirtual ? rowCount : rows.length;
this.treeArray = new Array(n);
for (let i = 0; i < n; ++i) {
this.treeArray[i] = 0;
}
for (let i = 0; i < n; ++i) {
const row = rows[i];
let currentRowHeight = rowHeight;
if (isFn) {
currentRowHeight = rowHeight(row);
}
// Add the detail row height to the already expanded rows.
// This is useful for the table that goes through a filter or sort.
const expanded = rowExpansions.has(row);
if (row && expanded) {
if (isDetailFn) {
const index = rowIndexes.get(row);
currentRowHeight += detailRowHeight(row, index);
} else {
currentRowHeight += detailRowHeight;
}
}
this.update(i, currentRowHeight);
}
}
/**
* Given the ScrollY position i.e. sum, provide the rowIndex
* that is present in the current view port. Below handles edge cases.
*/
getRowIndex(scrollY: number): number {
if (scrollY === 0) return 0;
return this.calcRowIndex(scrollY);
}
/**
* When a row is expanded or rowHeight is changed, update the height. This can
* be utilized in future when Angular Data table supports dynamic row heights.
*/
update(atRowIndex: number, byRowHeight: number): void {
if (!this.treeArray.length) {
throw new Error(`Update at index ${atRowIndex} with value ${byRowHeight} failed:
Row Height cache not initialized.`);
}
const n = this.treeArray.length;
atRowIndex |= 0;
while (atRowIndex < n) {
this.treeArray[atRowIndex] += byRowHeight;
atRowIndex |= atRowIndex + 1;
}
}
/**
* Range Sum query from 1 to the rowIndex
*/
query(atIndex: number): number {
if (!this.treeArray.length) {
throw new Error(`query at index ${atIndex} failed: Fenwick tree array not initialized.`);
}
let sum = 0;
atIndex |= 0;
while (atIndex >= 0) {
sum += this.treeArray[atIndex];
atIndex = (atIndex & (atIndex + 1)) - 1;
}
return sum;
}
/**
* Find the total height between 2 row indexes
*/
queryBetween(atIndexA: number, atIndexB: number): number {
return this.query(atIndexB) - this.query(atIndexA - 1);
}
/**
* Given the ScrollY position i.e. sum, provide the rowIndex
* that is present in the current view port.
*/
private calcRowIndex(sum: number): number {
if (!this.treeArray.length) return 0;
let pos = -1;
const dataLength = this.treeArray.length;
// Get the highest bit for the block size.
const highestBit = Math.pow(2, dataLength.toString(2).length - 1);
for (let blockSize = highestBit; blockSize !== 0; blockSize >>= 1) {
const nextPos = pos + blockSize;
if (nextPos < dataLength && sum >= this.treeArray[nextPos]) {
sum -= this.treeArray[nextPos];
pos = nextPos;
}
}
return pos + 1;
}
}