package main

import (
    "fmt"
    "image"
    "image/color"
    "log"

    "periph.io/x/devices/v3/screen1d"
    "periph.io/x/conn/v3/display"
    "periph.io/x/conn/v3/spi/spireg"
    "periph.io/x/devices/v3/apa102"
    "periph.io/x/host/v3"
)

func main() {
    if _, err := host.Init(); err != nil {
        log.Fatal(err)
    }
    d := getLEDs()
    img := image.NewNRGBA(d.Bounds())
    for x := 0; x < img.Rect.Max.X; x++ {
        img.SetNRGBA(x, 0, colorWheel(float64(x)/float64(img.Rect.Max.X)))
    }
    if err := d.Draw(d.Bounds(), img, image.Point{}); err != nil {
        log.Fatal(err)
    }
    fmt.Printf("\n")
}

// getLEDs returns an *apa102.Dev, or fails back to *screen1d.Dev if no SPI port
// is found.
func getLEDs() display.Drawer {
    s, err := spireg.Open("")
    if err != nil {
        fmt.Printf("Failed to find a SPI port, printing at the console:\n")
        return screen1d.New(&screen1d.Opts{X: 100})
    }
    // Change the option values to see their effects.
    opts := apa102.DefaultOpts
    d, err := apa102.New(s, &opts)
    if err != nil {
        log.Fatal(err)
    }
    return d
}

// colorWheel returns a HSV color wheel.
func colorWheel(h float64) color.NRGBA {
    h *= 6
    switch {
    case h < 1.:
        return color.NRGBA{R: 255, G: byte(255 * h), A: 255}
    case h < 2.:
        return color.NRGBA{R: byte(255 * (2 - h)), G: 255, A: 255}
    case h < 3.:
        return color.NRGBA{G: 255, B: byte(255 * (h - 2)), A: 255}
    case h < 4.:
        return color.NRGBA{G: byte(255 * (4 - h)), B: 255, A: 255}
    case h < 5.:
        return color.NRGBA{R: byte(255 * (h - 4)), B: 255, A: 255}
    default:
        return color.NRGBA{R: 255, B: byte(255 * (6 - h)), A: 255}
    }
}