// linear congruential generator written in go
// by darkmage
// https://www.evildojo.com
// https://www.twitter.com/evildojo666

package main

import (
    "fmt"
    "time"
    "os"
    "math"
    "math/rand"
    "strconv"
    "sync"
)

// define a global sieve
var sieve []bool
var wg sync.WaitGroup


func run_sieve(max int64, start int64, move int64, shard_num int64, shard_count int64) {
    var current int64 = start + shard_num
    if current > max-1 {
        current = current % max
    }
    for i := int64(0); i <= max/shard_count; i++ {
        sieve[current] = true
        current = current + move 
        if current > max-1 {
            current = current % max
        }
    }
    defer wg.Done()
}


func main() {
    if len(os.Args) != 3 {
        fmt.Println("Usage: go run main.go <seed> <shard_count>")
        os.Exit(1)
    }
    seed, err := strconv.ParseInt(os.Args[1], 10, 64)
    if err != nil {
        fmt.Println("Error: ", err)
        os.Exit(1)
    }
    rand := rand.New(rand.NewSource(seed))
    var max int64 = 256*256*256*256
    var start int64 = rand.Int63n(max)
    fmt.Println("start:", start)
    shard_count, err := strconv.ParseInt(os.Args[2], 10, 64)
    if err != nil {
        fmt.Println("Error: ", err)
        os.Exit(1)
    }
    fmt.Println("shard_count:", shard_count)
    var move int64 = (int64(math.Sqrt(float64(max))) + 1) * shard_count
    fmt.Println("move:", move)
    sieve = make([]bool, max)
    start_time := time.Now()
    for i := int64(0); i < shard_count; i++ {
        fmt.Println("shard:", i)
        wg.Add(1)
        go run_sieve(max, start, move, i, shard_count)
    }
    wg.Wait()
    end_time := time.Now()
    fmt.Println("Completed iterating numbers")
    fmt.Println("Time elapsed:", end_time.Sub(start_time))
    fmt.Println("Checking sieve")
    start_time = time.Now()
    for i := int64(0); i < max; i++ {
        if !sieve[i] {
            fmt.Println(os.Stderr, "Error, not all numbers flipped")
            os.Exit(1)
        }
    }
    end_time = time.Now()
    fmt.Println("Time elapsed:", end_time.Sub(start_time))
}