import type { BrushRect } from './types'

/**
 * Returns integer dataIndices covered by a brush rectangle on a category axis.
 *
 * `xStart` / `xEnd` come from `instance.convertFromPixel({ xAxisIndex: 0 }, …)`
 * which, for a category axis, returns fractional positions around integer
 * category indices (e.g. `1.3` lands between categories 1 and 2). We snap the
 * range outward (`floor` / `ceil`) so a drag that visually covers any part of
 * a category's bar includes that index.
 *
 * Results are clamped to `[0, dataLength - 1]` and returned in ascending order.
 */
export function hitTestCategoryRange(
  xStart: number,
  xEnd: number,
  dataLength: number,
): number[] {
  if (dataLength <= 0) return []
  const [lo, hi] = xStart <= xEnd ? [xStart, xEnd] : [xEnd, xStart]

  const start = Math.max(0, Math.floor(lo))
  const end = Math.min(dataLength - 1, Math.ceil(hi))
  if (start > end) return []

  const indices: number[] = []
  for (let i = start; i <= end; i += 1) indices.push(i)
  return indices
}

/**
 * Union of `hitTestCategoryRange` across multiple rectangles. Used for
 * multi-brush selections where each drawn rectangle contributes to the
 * combined selection.
 */
export function hitTestRects(rects: BrushRect[], dataLength: number): number[] {
  if (rects.length === 0) return []
  const seen = new Set<number>()
  for (const rect of rects) {
    for (const i of hitTestCategoryRange(rect.xStart, rect.xEnd, dataLength)) {
      seen.add(i)
    }
  }
  return Array.from(seen).sort((a, b) => a - b)
}