package main

import "fmt"
import "time"

func source(dst chan int) {
    for k := 1; k <= 100000; k++ {
        dst <- k*(k + 1)/2
    }
    close(dst)
}

func makePairs(src chan int, dst chan [2]int) {
    var v1, v2 int
    var ok1, ok2 bool
    for {
        v1, ok1 = <-src
        v2, ok2 = <-src
        if !(ok1 && ok2) {
            break
        }
        dst <- [2]int{v1, v2}
    }
    close(dst)
}

func split(src chan [2]int, dst1 chan [2]int, dst2 chan [2]int) {
    for chunk := range src {
        dst1 <- chunk
        dst2 <- chunk
    }
    close(dst1)
    close(dst2)
}

func multiply(src chan [2]int, dst chan int) {
    for chunk := range src {
        dst <- chunk[0]*chunk[1]
    }
    close(dst)
}

func gcd(src chan [2]int, dst chan int) {
    var helper func(int, int)
    helper = func(x int, y int) {
        if x < y {
            helper(y, x)
        } else if y == 0 {
            dst <- x
        } else {
            helper(y, x % y)
        }
    }
    for chunk := range src {
        helper(chunk[0], chunk[1])
    }
    close(dst)
}

func combine(src1 chan int, src2 chan int, dst chan [2]int) {
    var v1, v2 int
    var ok1, ok2 bool
    for {
        v1, ok1 = <-src1
        v2, ok2 = <-src2
        if !(ok1 && ok2) {
            break
        }
        dst <- [2]int{v1, v2}
    }
    close(dst)
}

func divide(src chan [2]int, dst chan int) {
    for chunk := range src {
        dst <- chunk[0]/chunk[1]
    }
    close(dst)
}

func getDigits(src chan int, dst chan int) {
    var helper func(int)
    helper = func(x int) {
        if x != 0 {
            helper(x/10)
            dst <- x % 10
        }
    }
    for chunk := range src {
        helper(chunk)
    }
    close(dst)
}

func sink(src chan int) {
    for _ = range src {
    }
}

func pipeline() {
    // Channels are unbuffered for a fair comparison with generators
    c1 := make(chan int)
    c2 := make(chan [2]int)
    c3 := make(chan [2]int)
    c4 := make(chan [2]int)
    c5 := make(chan int)
    c6 := make(chan int)
    c7 := make(chan [2]int)
    c8 := make(chan int)
    c9 := make(chan int)
    go source(c1)
    go makePairs(c1, c2)
    go split(c2, c3, c4)
    go multiply(c3, c5)
    go gcd(c4, c6)
    go combine(c5, c6, c7)
    go divide(c7, c8)
    go getDigits(c8, c9)
    sink(c9)
}

func main() {
    timer := time.Now()
    for i := 0; i < 100; i++ {
        pipeline()
    }
    fmt.Println(time.Now().Sub(timer))
}