package main

import (
    "encoding/json"
    "fmt"
    "io/ioutil"
    "net/http"
    "sync"
)

type Story struct {
    Title string
}

func main() {
    rsp, err := http.Get("https://hacker-news.firebaseio.com/v0/topstories.json")
    if err != nil {
        panic(err)
    }
    defer rsp.Body.Close()

    data, err := ioutil.ReadAll(rsp.Body)
    if err != nil {
        panic(err)
    }

    var ids []int
    if err := json.Unmarshal(data, &ids); err != nil {
        panic(err)
    }

    var cursor int
    var mutex sync.Mutex

    next := func() int {
        mutex.Lock()
        defer mutex.Unlock()
        temp := cursor
        cursor++
        return temp
    }

    wg := sync.WaitGroup{}
    for i := 0; i < 8; i++ {
        wg.Add(1)
        go func() {
            for cursor := next(); cursor < len(ids); cursor = next() {
                url := fmt.Sprintf(
                    "https://hacker-news.firebaseio.com/v0/item/%d.json",
                    ids[cursor],
                )
                rsp, err := http.Get(url)
                if err != nil {
                    panic(err)
                }
                defer rsp.Body.Close()

                data, err := ioutil.ReadAll(rsp.Body)
                if err != nil {
                    panic(err)
                }
                var story Story
                if err := json.Unmarshal(data, &story); err != nil {
                    panic(err)
                }
                fmt.Println(story.Title)
            }
            wg.Done()
        }()
    }

    wg.Wait()
}