Implement undoing

instruction.go

@@ -49,12 +49,36 @@ func (instruction *LinkInstruction) String() string {
 		flagsStr = " [" + strings.Join(flags, ", ") + "]"
 	}
 
-	return fmt.Sprintf("%s%s%s → %s%s%s%s",
-		SourceColor, instruction.Source, DefaultColor,
-		TargetColor, instruction.Target, DefaultColor,
+	return fmt.Sprintf("%s → %s%s",
+		FormatSourcePath(instruction.Source),
+		FormatTargetPath(instruction.Target),
 		flagsStr)
 }
 
+func (instruction *LinkInstruction) Undo() {
+	if !FileExists(instruction.Target) {
+		return
+	}
+
+	isSymlink, err := IsSymlink(instruction.Target)
+	if err != nil {
+		LogError("could not determine whether %s is a sym link or not, stopping; err: %v",
+			FormatTargetPath(instruction.Target), err)
+		return
+	}
+
+	if isSymlink {
+		LogInfo("Removing symlink at %s", FormatTargetPath(instruction.Target))
+		err = os.Remove(instruction.Target)
+		if err != nil {
+			LogError("could not remove symlink at %s; err: %v",
+				FormatTargetPath(instruction.Target), err)
+		}
+	} else {
+		LogInfo("%s is not a symlink, skipping", FormatTargetPath(instruction.Target))
+	}
+}
+
 func ParseInstruction(line, workdir string) (LinkInstruction, error) {
 	line = strings.TrimSpace(line)
 	if strings.HasPrefix(line, "#") {
@@ -131,6 +155,11 @@ func isTrue(value string) bool {
 
 func (instruction *LinkInstruction) RunAsync(status chan (error)) {
 	defer close(status)
+	if undo {
+		instruction.Undo()
+		return
+	}
+
 	if !FileExists(instruction.Source) {
 		status <- fmt.Errorf("instruction source %s does not exist", FormatSourcePath(instruction.Source))
 		return