andreychernih/railsbox

package main

import (
    "github.com/jinzhu/gorm"
    "io"
    "log"
    "net/http"
    "os"
)

func downloadWorker(db gorm.DB, gems <-chan string, done chan<- bool) {
    for gem := range gems {
        gemRecord := Gem{}
        db.Where(&Gem{Name: gem}).First(&gemRecord)
        outputPath := gemRecord.GetFilePath()

        if _, err := os.Stat(outputPath); os.IsNotExist(err) {
            log.Printf("Downloading %s to %s", gem, outputPath)

            out, err := os.Create(outputPath)
            handleError(err)
            defer out.Close()

            resp, err := http.Get(gemRecord.GemUrl)
            handleError(err)
            defer resp.Body.Close()

            _, err1 := io.Copy(out, resp.Body)
            handleError(err1)
        }
    }
    done <- true
}

func Download(gr *GemRepository) {
    const downloadConcurrency = 5

    gemChan := make(chan string)
    doneChan := make(chan bool)

    for i := 0; i < downloadConcurrency; i++ {
        go downloadWorker(gr.db, gemChan, doneChan)
    }

    gems := gr.DownloadQueue()
    for _, gem := range gems {
        gemChan <- gem
    }

    close(gemChan)

    for i := 0; i < downloadConcurrency; i++ {
        <-doneChan
    }
}