squiggle/packages/squiggle-lang/src/rescript/utility/Sparklines.res

// Port of Sindre Sorhus' Sparkly to Rescript
// reference implementation: https://github.com/sindresorhus/sparkly
// Omitting rgb "fire" style, so no `chalk` dependency

type sparklyConfig = {
  minimum: option<float>,
  maximum: option<float>
}

let sparkly = (
  numbers: array<float>,
  ~options = {minimum: None, maximum: None}
) => {
  // Unlike reference impl, we assume that all numbers are finite, i.e. no NaN.

  let ticks = [`▁`, `▂`, `▃`, `▄`, `▅`, `▆`, `▇`, `█`]

  let minimum = E.O.default(Js.Math.minMany_float(numbers), options.minimum)
  let maximum = E.O.default(Js.Math.maxMany_float(numbers), options.maximum)

  // Use a high tick if data is constant and max is not equal
  let ticks = if minimum == maximum && maximum != 0.0 {
    [ticks[4]]
  } else {
    ticks
  }

  let toMapWith = (number: float) => {
    let tickIndex = Js.Math.ceil_int((number /. maximum) *. Belt.Int.toFloat(Belt.Array.length(ticks))) - 1

    let tickIndex = if maximum == 0.0 || tickIndex < 0 {
        0
      } else {
        tickIndex
      }

    ticks[tickIndex]
  }
  Js.Array.joinWith("", Belt.Array.map(numbers, toMapWith))
}