Van Eck Sequence in Go.

van-eck-sequence.go

// Van Eck Sequence

// Run with: `go run van-eck-sequence.go`

package main

import (
	"flag"
	"fmt"
	"os"
	"os/signal"
	"syscall"
	"time"
)

var delay int = 100
var perline int = 50
var separator string = ", "
var runs int = 0
var sequence = []int{0}

func init() {
	flag.IntVar(&delay, "d", delay, "Delay between numbers in ms. Can be 0.")
	flag.IntVar(&perline, "p", perline, "Wrap at this amount of numbers output.")
	flag.StringVar(&separator, "s", separator, "Something to delineate the different numbers. Or not.")
	flag.IntVar(&runs, "r", runs, "Maximum amount of numbers output. 0 means infinite, or thereabouts.")
	flag.Parse()

	if delay < 0 {
		panic("Invalid delay: that would involve time travel.")
	}
	if perline < 1 {
		panic("Invalid numbers-per-line setting. Don't be an idiot.")
	}
	if len(separator) > 5 {
		panic("You're using more than 5 characters to delineate numbers? Are you okay?")
	}
	if runs < 0 {
		panic("Well, that's a bit pointless.")
	}
}

func main () {
	seen := map[int]int{}

	closeHandler()

	for i, s := range sequence {
		seen[s] = i + 1
	}

	for {
		key := sequence[len(sequence)-1]
		value := len(sequence)-1

		if seen[key] == 0 {
			seen[key] = value + 1
			sequence = append(sequence, 0)

		} else {
			sequence = append(sequence, value + 1 - seen[key])
			seen[key] = value + 1
		}

		fmt.Printf("%d%s", key, separator)
		if (len(sequence)-1) % perline == 0 {
			fmt.Println()
		}

		if runs > 0 && len(sequence) == runs {
			fmt.Printf("\nCompleted %d runs.\n", runs)
			doOutput()
			createGraph()
			break
		}

		time.Sleep(time.Duration(int(delay)) * time.Millisecond)
	}
}

func closeHandler() {
	c := make(chan os.Signal)
	signal.Notify(c, os.Interrupt, syscall.SIGTERM)
	go func() {
		<-c
		fmt.Println("\nCtrl+C pressed, quitting...")
		doOutput()
		createGraph()
		os.Exit(0)
	}()
}

func doOutput() {
	fmt.Println(sequence)
}

func createGraph() {
	fmt.Println("Creating image, will just be a sec...")
}