Make --dry-run a bit smarter and more useful

commands/command_push.go

@@ -23,25 +23,42 @@ var (
 )
 
 func pushCommand(cmd *cobra.Command, args []string) {
-	refsData, err := ioutil.ReadAll(os.Stdin)
-	if err != nil {
-		Panic(err, "Error reading refs on stdin")
-	}
+	var left, right string
 
-	if len(refsData) == 0 {
-		return
-	}
+	if dryRun {
+		if len(args) != 2 {
+			Print("Usage: git media push --dry-run <repo> <refspec>")
+			return
+		}
+
+		ref, err := gitmedia.CurrentRef()
+		if err != nil {
+			Panic(err, "Error getting current ref")
+		}
+		left = ref
+		right = fmt.Sprintf("^%s/%s", args[0], args[1])
+	} else {
+		refsData, err := ioutil.ReadAll(os.Stdin)
+		if err != nil {
+			Panic(err, "Error reading refs on stdin")
+		}
+
+		if len(refsData) == 0 {
+			return
+		}
+
+		left, right = decodeRefs(string(refsData))
+		if left == deleteBranch {
+			return
+		}
 
-	left, right := decodeRefs(string(refsData))
-	if left == deleteBranch {
-		return
 	}
 
 	links := linksFromRefs(left, right)
 
 	for i, link := range links {
 		if dryRun {
-			fmt.Println("push", link.Oid, link.Name)
+			Print("push %s", link.Name)
 			continue
 		}
 		if wErr := pushAsset(link.Oid, link.Name, i+1, len(links)); wErr != nil {

gitmedia/gitmedia.go

@@ -1,11 +1,13 @@
 package gitmedia
 
 import (
+	"errors"
 	"fmt"
 	"github.com/github/git-media/git"
 	"io/ioutil"
 	"os"
 	"path/filepath"
+	"regexp"
 	"runtime"
 	"strings"
 )
@@ -83,6 +85,33 @@ func InRepo() bool {
 	return LocalWorkingDir != ""
 }
 
+var shaMatcher = regexp.MustCompile(`^[0-9a-f]{40}`)
+
+func CurrentRef() (string, error) {
+	head, err := ioutil.ReadFile(filepath.Join(LocalGitDir, "HEAD"))
+	if err != nil {
+		return "", err
+	}
+
+	if shaMatcher.Match(head) {
+		return strings.TrimSpace(string(head)), nil
+	}
+
+	headString := string(head)
+	parts := strings.Split(headString, " ")
+	if len(parts) != 2 {
+		return "", errors.New("Unable to parse HEAD")
+	}
+
+	refFile := strings.TrimSpace(parts[1])
+	sha, err := ioutil.ReadFile(filepath.Join(LocalGitDir, refFile))
+	if err != nil {
+		return "", err
+	}
+
+	return strings.TrimSpace(string(sha)), nil
+}
+
 func init() {
 	var err error
 	LocalWorkingDir, LocalGitDir, err = resolveGitDir()