okp4/ui

/* eslint-disable functional/no-loop-statement */
/* eslint-disable functional/no-let */
/* eslint-disable @typescript-eslint/prefer-readonly-parameter-types */
export type Star = {
  x: number
  y: number
  z: number
  px: number
  py: number
}

const speed = 0.05

const moveStar = (s: Star): Star => {
  s.px = s.x
  s.py = s.y
  s.z += speed
  s.x += s.x * (speed * 0.2) * s.z
  s.y += s.y * (speed * 0.2) * s.z

  return s
}

const inBound =
  (width: number, height: number): ((s: Star) => boolean) =>
  (s: Star): boolean =>
    !(
      s.x > width / 2 + 50 ||
      s.x < -width / 2 - 50 ||
      s.y > height / 2 + 50 ||
      s.y < -height / 2 - 50
    )

const drawStar =
  (canvas: HTMLCanvasElement): ((s: Star) => Star) =>
  (s: Star): Star => {
    const ctx = canvas.getContext('2d')

    if (ctx) {
      ctx.strokeStyle = `rgb(176,224,230)`
      ctx.lineWidth = s.z / 2
      ctx.beginPath()
      ctx.moveTo(s.x, s.y)
      ctx.lineTo(s.px, s.py)
      ctx.stroke()
    }

    return s
  }

function* starsGen(nb: number, width: number, height: number): Generator<Star> {
  for (let i = 0; i < nb; i++) {
    const x = Math.random() * width - width / 2
    const y = Math.random() * height - height / 2
    const star: Star = {
      x: x,
      y: y,
      z: Math.random() * 2,
      px: x,
      py: y
    }

    yield star
  }
}

const S = {
  cw: 0,
  ch: 0,
  stars: [] as Star[]
}

export const drawStarField =
  (
    nbStars: number
  ): (({ canvas, deltaCount }: { canvas: HTMLCanvasElement; deltaCount: number }) => void) =>
  ({ canvas }: { canvas: HTMLCanvasElement }): void => {
    const ctx = canvas.getContext('2d')
    const [w, h]: [number, number] = [canvas.width, canvas.height]

    if (ctx) {
      ctx.resetTransform()
      ctx.fillStyle = 'black'
      ctx.fillRect(0, 0, w, h)
      ctx.translate(w / 2, h / 2)

      if (S.cw !== w || S.ch !== h) {
        S.cw = w
        S.ch = h
        S.stars = []
      }

      if (S.stars.length < nbStars) {
        S.stars = [...S.stars, ...starsGen(nbStars, w, h)]
      }

      S.stars = Array.from(S.stars).map(drawStar(canvas)).map(moveStar).filter(inBound(w, h))
    }
  }