// Channel Benchmark
//
// `nobj` integers are sent thru a channel with queue length`buflen`
// using `nsend` sender threads and `nrec` receiver threads.
//
// The receive threads add all received numbers and send them to the
// main thread where the total sum is compare to the expected value.
import time
import os

fn do_rec(ch chan int, resch chan i64, n int) {
    mut sum := i64(0)
    for _ in 0 .. n {
        sum += <-ch
    }
    println(sum)
    resch <- sum
}

fn do_send(ch chan int, start int, end int) {
    for i in start .. end {
        ch <- i
    }
}

fn main() {
    if os.args.len != 5 {
        eprintln('usage:\n\t${os.args[0]} <nsend> <nrec> <buflen> <nobj>')
        exit(1)
    }
    nsend := os.args[1].int()
    nrec := os.args[2].int()
    buflen := os.args[3].int()
    nobj := os.args[4].int()
    stopwatch := time.new_stopwatch()
    ch := chan int{cap: buflen}
    resch := chan i64{}
    mut no := nobj
    for i in 0 .. nrec {
        n := no / (nrec - i)
        spawn do_rec(ch, resch, n)
        no -= n
    }
    $if debug {
        assert no == 0
    }
    no = nobj
    for i in 0 .. nsend {
        n := no / (nsend - i)
        end := no
        no -= n
        spawn do_send(ch, no, end)
    }
    assert no == 0
    mut sum := i64(0)
    for _ in 0 .. nrec {
        sum += <-resch
    }
    elapsed := stopwatch.elapsed()
    rate := f64(nobj) / elapsed * time.microsecond
    println('${nobj} objects in ${f64(elapsed) / time.second} s (${rate:.2f} objs/µs)')
    // use sum formula by Gauß to calculate the expected result
    expected_sum := i64(nobj) * (nobj - 1) / 2
    println('got: ${sum}, expected: ${expected_sum}')
    assert sum == expected_sum
}