refactor: restructure project

internal/downloader/downloader.go

@@ -0,0 +1,87 @@
+package downloader
+
+import (
+	"errors"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+
+	req "github.com/levigross/grequests"
+	"github.com/schollz/progressbar/v3"
+)
+
+var (
+	ErrAccessDenied     = errors.New("restricted access (credentials required)")
+	ErrInvalidURL       = errors.New("invalid url")
+	ErrUnknownAuthority = errors.New("certificate from unknown authority")
+)
+
+type Context struct {
+	Filename string
+	Link     string
+}
+
+func NewContext(filename, link string) *Context {
+	return &Context{
+		Filename: filename,
+		Link:     link,
+	}
+}
+
+func (c *Context) Download() error {
+	resp, err := req.Head(c.Link, nil)
+	if err != nil {
+		if strings.Contains(err.Error(), "no such host") {
+			return ErrInvalidURL
+		}
+		if strings.Contains(err.Error(), "certificate signed by unknown authority") {
+			return ErrUnknownAuthority
+		}
+		return err
+	}
+	defer resp.Close()
+	if resp.StatusCode == http.StatusNotFound {
+		return ErrInvalidURL
+	}
+	if resp.StatusCode == http.StatusUnauthorized {
+		return ErrAccessDenied
+	}
+	if resp.StatusCode != http.StatusOK {
+		return errors.New(resp.RawResponse.Status)
+	}
+	resp.Close()
+
+	resp, err = req.Get(c.Link, nil)
+	if err != nil {
+		return err
+	}
+
+	var filesize int64
+	if resp.RawResponse.ContentLength > -1 {
+		filesize = resp.RawResponse.ContentLength
+	}
+
+	destFile, err := os.OpenFile(c.Filename, os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	defer destFile.Close()
+
+	bar := progressbar.DefaultBytes(
+		filesize,
+		"downloading",
+	)
+
+	_, err = io.Copy(io.MultiWriter(destFile, bar), resp.RawResponse.Body)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (c *Context) FileExists() bool {
+	_, err := os.Stat(c.Filename)
+	return !errors.Is(err, os.ErrNotExist)
+}