/**
 * Given a scale ( bp/px ) and minimum distances (px) between major and minor
 * gridlines, return an object like `{ majorPitch: bp, minorPitch: bp }` giving
 * the gridline pitches to use.
 */
export function chooseGridPitch(
  scale: number,
  minMajorPitchPx: number,
  minMinorPitchPx: number,
) {
  scale = Math.abs(scale)
  const minMajorPitchBp = minMajorPitchPx * scale
  const majorMagnitude = Number.parseInt(
    minMajorPitchBp.toExponential().split(/e/i)[1]!,
    10,
  )

  let majorPitch = 10 ** majorMagnitude
  while (majorPitch < minMajorPitchBp) {
    majorPitch *= 2
    if (majorPitch >= minMajorPitchBp) {
      break
    }
    majorPitch *= 2.5
  }

  majorPitch = Math.max(majorPitch, 5)

  const majorPitchPx = majorPitch / scale

  let minorPitch = 0
  if (!(majorPitch % 10) && majorPitchPx / 10 >= minMinorPitchPx) {
    minorPitch = majorPitch / 10
  } else if (!(majorPitch % 5) && majorPitchPx / 5 >= minMinorPitchPx) {
    minorPitch = majorPitch / 5
  } else if (!(majorPitch % 2) && majorPitchPx / 2 >= minMinorPitchPx) {
    minorPitch = majorPitch / 2
  }

  return { majorPitch, minorPitch }
}
export function makeTicks(
  start: number,
  end: number,
  bpPerPx: number,
  emitMajor = true,
  emitMinor = true,
) {
  const gridPitch = chooseGridPitch(bpPerPx, 60, 15)

  let minBase = start
  let maxBase = end

  if (bpPerPx < 0) {
    ;[minBase, maxBase] = [maxBase, minBase]
  }

  // add 20px additional on the right and left to allow us to draw the ends of
  // labels that lie a little outside our region
  minBase -= Math.abs(20 * bpPerPx)
  maxBase += Math.abs(20 * bpPerPx) + 1

  const iterPitch = gridPitch.minorPitch || gridPitch.majorPitch
  let index = 0
  const ticks = []
  for (
    let base = Math.ceil(minBase / iterPitch) * iterPitch;
    base < maxBase;
    base += iterPitch
  ) {
    if (emitMinor && base % (gridPitch.majorPitch * 2)) {
      ticks.push({ type: 'minor', base: base - 1, index })
      index += 1
    } else if (emitMajor && !(base % (gridPitch.majorPitch * 2))) {
      ticks.push({ type: 'major', base: base - 1, index })
      index += 1
    }
  }
  return ticks
}

export function mathPower(num: number): string {
  if (num < 999) {
    return String(num)
  }
  return `${mathPower(~~(num / 1000))},${`00${~~(num % 1000)}`.slice(
    -3,
    -3 + 3,
  )}`
}