/** * Copyright (c) Meta Platforms, Inc. and affiliates. * * This source code is licensed under the MIT license found in the * LICENSE file in the root directory of this source tree. * * @flow strict * @format */ import invariant from 'invariant'; export type CellRegion = { first: number, last: number, isSpacer: boolean, }; export class CellRenderMask { _numCells: number; _regions: Array; constructor(numCells: number) { invariant( numCells >= 0, 'CellRenderMask must contain a non-negative number os cells', ); this._numCells = numCells; if (numCells === 0) { this._regions = []; } else { this._regions = [ { first: 0, last: numCells - 1, isSpacer: true, }, ]; } } enumerateRegions(): $ReadOnlyArray { return this._regions; } addCells(cells: {first: number, last: number}): void { invariant( cells.first >= 0 && cells.first < this._numCells && cells.last >= -1 && cells.last < this._numCells && cells.last >= cells.first - 1, 'CellRenderMask.addCells called with invalid cell range', ); // VirtualizedList uses inclusive ranges, where zero-count states are // possible. E.g. [0, -1] for no cells, starting at 0. if (cells.last < cells.first) { return; } const [firstIntersect, firstIntersectIdx] = this._findRegion(cells.first); const [lastIntersect, lastIntersectIdx] = this._findRegion(cells.last); // Fast-path if the cells to add are already all present in the mask. We // will otherwise need to do some mutation. if (firstIntersectIdx === lastIntersectIdx && !firstIntersect.isSpacer) { return; } // We need to replace the existing covered regions with 1-3 new regions // depending whether we need to split spacers out of overlapping regions. const newLeadRegion: Array = []; const newTailRegion: Array = []; const newMainRegion: CellRegion = { ...cells, isSpacer: false, }; if (firstIntersect.first < newMainRegion.first) { if (firstIntersect.isSpacer) { newLeadRegion.push({ first: firstIntersect.first, last: newMainRegion.first - 1, isSpacer: true, }); } else { newMainRegion.first = firstIntersect.first; } } if (lastIntersect.last > newMainRegion.last) { if (lastIntersect.isSpacer) { newTailRegion.push({ first: newMainRegion.last + 1, last: lastIntersect.last, isSpacer: true, }); } else { newMainRegion.last = lastIntersect.last; } } const replacementRegions: Array = [ ...newLeadRegion, newMainRegion, ...newTailRegion, ]; const numRegionsToDelete = lastIntersectIdx - firstIntersectIdx + 1; this._regions.splice( firstIntersectIdx, numRegionsToDelete, ...replacementRegions, ); } numCells(): number { return this._numCells; } equals(other: CellRenderMask): boolean { return ( this._numCells === other._numCells && this._regions.length === other._regions.length && this._regions.every( (region, i) => region.first === other._regions[i].first && region.last === other._regions[i].last && region.isSpacer === other._regions[i].isSpacer, ) ); } _findRegion(cellIdx: number): [CellRegion, number] { let firstIdx = 0; let lastIdx = this._regions.length - 1; while (firstIdx <= lastIdx) { const middleIdx = Math.floor((firstIdx + lastIdx) / 2); const middleRegion = this._regions[middleIdx]; if (cellIdx >= middleRegion.first && cellIdx <= middleRegion.last) { return [middleRegion, middleIdx]; } else if (cellIdx < middleRegion.first) { lastIdx = middleIdx - 1; } else if (cellIdx > middleRegion.last) { firstIdx = middleIdx + 1; } } invariant(false, `A region was not found containing cellIdx ${cellIdx}`); } }