Ardan exercise

main.go

package main

import (
	"fmt"
	"net/http"
	"sync"
	"time"
)

func downloadSize(startDate, endDate time.Time) (int64, error) {
	const base = "https://d37ci6vzurychx.cloudfront.net/trip-data/%s_tripdata_%d-%d.parquet"

	sizeCh := make(chan int64)

	var wg sync.WaitGroup
	for _, colour := range []string{"yellow", "green"} {
		for date := startDate; !date.After(endDate); date = addMonth(date, 1) {
			wg.Add(1)
			go func(date time.Time, colour string) {
				url := fmt.Sprintf(base, colour, date.Year(), date.Month())
				req, err := http.NewRequest("HEAD", url, nil)
				if err != nil {
					panic(err)
				}

				resp, err := http.DefaultClient.Do(req)
				if err != nil {
					panic(err)
				}
				sizeCh <- resp.ContentLength
				wg.Done()
			}(date, colour)
		}
	}

	var totalSize int64
	go func() {
		for size := range sizeCh {
			totalSize += size
		}
	}()

	wg.Wait()
	close(sizeCh)

	return totalSize, nil
}

func addMonth(t time.Time, m int) time.Time {
	x := t.AddDate(0, m, 0)
	if d := x.Day(); d != t.Day() {
		return x.AddDate(0, 0, -d)
	}
	return x
}

func main() {
	now := time.Now()
	yesteryear := now.AddDate(-1, 0, 0)
	size, err := downloadSize(yesteryear, now)
	if err != nil {
		panic(err)
	}

	fmt.Println(size)
}