Add ability to add box

This only works for boxes being added as username/boxname from
vagrant cloud.

internal/core/actions.go

@@ -0,0 +1,82 @@
+package core
+
+import (
+	"io"
+	"io/ioutil"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const VagrantCloudUrl = "http://app.vagrantup.com"
+
+func downloadBox(url string, destination string) (err error) {
+	resp, err := http.Get(url)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	out, err := os.Create(destination)
+	if err != nil {
+		return err
+	}
+	defer out.Close()
+
+	_, err = io.Copy(out, resp.Body)
+	return
+}
+
+func constructMetadataUrl(username, boxname string) string {
+	url := VagrantCloudUrl + "/" + username + "/boxes/" + boxname + ".json"
+	return url
+}
+
+func addBox(name, provider string, basis *Basis) (box *Box, err error) {
+	// Assume the name is of for <user>/<box>
+	s := strings.Split(name, "/")
+	metadataUrl := constructMetadataUrl(s[0], s[1])
+
+	// Download the metadata
+	resp, err := http.Get(metadataUrl)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	raw, err := ioutil.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	metadata, err := LoadBoxMetadata(raw)
+	if err != nil {
+		return nil, err
+	}
+	versions, _ := metadata.ListVersions(&BoxVersionProvider{Name: provider})
+	// latest version is first
+	version, _ := metadata.Version(versions[0], &BoxVersionProvider{Name: provider})
+	providerMeta, err := version.Provider(provider)
+	downloadUrl := providerMeta.Url
+
+	boxTempName := s[0] + "-" + s[1] + "-" + strconv.FormatInt(time.Now().Unix(), 10) + ".box"
+	boxDownloadPath := filepath.Join(basis.dir.TempDir().String(), boxTempName)
+
+	// Download the box
+	err = downloadBox(downloadUrl, boxDownloadPath)
+	if err != nil {
+		return nil, err
+	}
+	// Delete the downloaded file when done
+	defer os.RemoveAll(boxDownloadPath)
+
+	// Add the box to the box collection
+	boxes, _ := basis.Boxes()
+	returnBox, err := boxes.Add(boxDownloadPath, name, version.Version, metadataUrl, false, provider)
+	if err != nil {
+		return nil, err
+	}
+	returnBox.(*Box).Save()
+	return returnBox.(*Box), nil
+}