function diffBgra(a, b, options = {}) {
  if (!a || !b || a.length !== b.length) {
    throw new Error(`bitmap size mismatch: ${a?.length || 0} != ${b?.length || 0}`)
  }
  const perChannelTolerance = Number.isFinite(options.perChannelTolerance)
    ? options.perChannelTolerance
    : 2
  const maxMismatchedRatio = Number.isFinite(options.maxMismatchedRatio)
    ? options.maxMismatchedRatio
    : 0.001

  let mismatchedPixels = 0
  let maxDelta = 0
  let totalDelta = 0
  const pixels = a.length / 4

  for (let i = 0; i < a.length; i += 4) {
    let pixelMismatch = false
    for (let c = 0; c < 4; c += 1) {
      const delta = Math.abs(a[i + c] - b[i + c])
      maxDelta = Math.max(maxDelta, delta)
      totalDelta += delta
      if (delta > perChannelTolerance) pixelMismatch = true
    }
    if (pixelMismatch) mismatchedPixels += 1
  }

  const mismatchedRatio = pixels ? mismatchedPixels / pixels : 0
  return {
    ok: mismatchedRatio <= maxMismatchedRatio,
    pixels,
    mismatchedPixels,
    mismatchedRatio,
    maxDelta,
    meanDelta: pixels ? totalDelta / (pixels * 4) : 0,
    perChannelTolerance,
    maxMismatchedRatio,
  }
}

module.exports = { diffBgra }