country-geo-locations/pkg/downloader/downloader.go

package downloader

import (
	"crypto/md5"
	"crypto/sha1"
	"crypto/sha256"
	"errors"
	"fmt"
	"hash"
	"io"
	"os"
	"strings"
	"time"

	"github.com/dustin/go-humanize"
	req "github.com/levigross/grequests"
)

var (
	hashes = map[string]hash.Hash{
		"md5":    md5.New(),  //nolint: gosec
		"sha1":   sha1.New(), //nolint: gosec
		"sha256": sha256.New(),
	}
)

type Context struct {
	Filename   string
	Filesize   int64
	Reader     io.Reader
	Chan       chan *Response
	Closer     []func() error
	hashWriter hash.Hash
}

func NewContext(filename string, filesize int64, hw hash.Hash, closer ...func() error) *Context {
	return &Context{
		Filename:   filename,
		Filesize:   filesize,
		Chan:       make(chan *Response),
		Closer:     closer,
		hashWriter: hw,
	}
}

func (ctx *Context) Checksum() string {
	return fmt.Sprintf("%x", ctx.hashWriter.Sum(nil))
}

func (ctx *Context) SetReader(rdr io.Reader) {
	ctx.Reader = io.TeeReader(
		rdr,
		io.MultiWriter(
			ctx.hashWriter,
			&ProgressWriter{
				Filename: ctx.Filename,
				Filesize: ctx.Filesize,
				Channel:  ctx.Chan,
				Start:    time.Now(),
			},
		),
	)
}

func (ctx *Context) Close() {
	for i := len(ctx.Closer) - 1; i >= 0; i-- {
		ctx.Closer[i]()
	}
}

type ProgressWriter struct {
	Channel  chan *Response
	Start    time.Time
	Filename string
	Filesize int64
	Bytes    int64
}

func (pw *ProgressWriter) Write(data []byte) (int, error) {
	pw.Bytes = pw.Bytes + int64(len(data))
	var progress float64
	if pw.Filesize > 0 {
		progress = float64(pw.Bytes) / float64(pw.Filesize) * 100
	}
	pw.Channel <- &Response{
		Progress:        progress,
		BytesPerSecond:  float64(pw.Bytes) / time.Since(pw.Start).Seconds(),
		BytesTransfered: pw.Bytes,
		BytesTotal:      pw.Filesize,
	}
	return len(data), nil
}

type File struct {
	URL      string
	Filename string
	Size     int64
}

type Response struct {
	Error           error
	Progress        float64
	BytesPerSecond  float64
	BytesTransfered int64
	BytesTotal      int64
}

func handleError(err error, adds ...string) {
	msg := err.Error()
	if len(adds) != 0 {
		msg = fmt.Sprintf("%s %s", msg, strings.Join(adds, " "))
	}
	fmt.Println(msg)
	os.Exit(0)
}

func printProgress(ctx *Context) {
	for {
		resp, ok := <-ctx.Chan
		if !ok {
			fmt.Println("\nSaved file to", ctx.Filename)
			for key, value := range hashes {
				fmt.Printf("%s: %x\n", key, value.Sum(nil))
			}
			break
		}
		if resp.Error != nil {
			handleError(resp.Error)
		}
		if resp.BytesTotal > 0 {
			fmt.Printf("\rDownloading %7s/%7s %.02f%%", humanize.Bytes(uint64(resp.BytesTransfered)), humanize.Bytes(uint64(resp.BytesTotal)), resp.Progress)
		} else {
			fmt.Printf("\rDownloading %7s", humanize.Bytes(uint64(resp.BytesTransfered)))
		}
	}
}

func DownloadFile(path, url string) {
	file := File{
		URL:      url,
		Filename: path,
	}
	response, err := req.Head(file.URL, nil)
	if err != nil {
		if strings.Contains(err.Error(), "no such host") {
			handleError(errors.New("invalid url"))
		} else if strings.Contains(err.Error(), "certificate signed by unknown authority") {
			handleError(errors.New("certificate signed by unknown authority"))
		}
		handleError(err)
	}
	defer response.Close()
	if response.StatusCode == 404 {
		handleError(errors.New("invalid url"))
	}
	if response.StatusCode == 401 {
		handleError(errors.New("restriced access, credentials required"))
	}
	response.Close()

	resp, err := req.Get(file.URL, nil)
	if err != nil {
		handleError(err)
	}

	var filesize int64
	if resp.RawResponse.ContentLength != -1 {
		filesize = resp.RawResponse.ContentLength
	}
	ctx := NewContext(file.Filename, filesize, md5.New())
	ctx.SetReader(resp.RawResponse.Body)

	go func(ctx *Context) {
		defer ctx.Close()

		dstFile, err := os.Create(ctx.Filename)
		if err != nil {
			ctx.Chan <- &Response{Error: err}
			close(ctx.Chan)
			return
		}
		defer dstFile.Close()

		writer := io.MultiWriter(dstFile, hashes["md5"], hashes["sha1"], hashes["sha256"])
		_, err = io.Copy(writer, ctx.Reader)
		if err != nil {
			ctx.Chan <- &Response{Error: err}
		}
		close(ctx.Chan)
	}(ctx)

	printProgress(ctx)
}

func FileExists(path string) bool {
	_, err := os.Stat(path)
	return !errors.Is(err, os.ErrNotExist)
}