package main

import (
    "bufio"
    "fmt"
    "io"
    "math"
    "os"
)

func rgb(i int) (int, int, int) {
    var f = 0.1
    return int(math.Sin(f*float64(i)+0)*127 + 128),
        int(math.Sin(f*float64(i)+2*math.Pi/3)*127 + 128),
        int(math.Sin(f*float64(i)+4*math.Pi/3)*127 + 128)
}


func main() {
    info, _ := os.Stdin.Stat()

    if info.Mode()&os.ModeCharDevice != 0 {
        fmt.Println("The command is intended to work with pipes.")
        fmt.Println("Usage: command | gorainbow")
    }

    reader := bufio.NewReader(os.Stdin)
    j := 0
    for {
        input, _, err := reader.ReadRune()
        if err != nil && err == io.EOF {
            break
        }
        r, g, b := rgb(j)
        fmt.Printf("\033[38;2;%d;%d;%dm%c\033[0m", r, g, b, input)
        j++
    }
}