Add IsInstalled API to installer interface

`IsInstalled(cmd, bin string) bool` will help tools using this library
to show a prompt to users asking if they would like to have completion
enabled.

1 files changed, 9 insertions, 4 deletions

diff --git a/cmd/install/zsh.go b/cmd/install/zsh.go
index a625f53..29950ab 100644
--- a/cmd/install/zsh.go
+++ b/cmd/install/zsh.go
@@ -11,12 +11,17 @@ type zsh struct {
 	rc string
 }
 
-func (z zsh) Install(cmd, bin string) error {
+func (z zsh) IsInstalled(cmd, bin string) bool {
 	completeCmd := z.cmd(cmd, bin)
-	if lineInFile(z.rc, completeCmd) {
+	return lineInFile(z.rc, completeCmd)
+}
+
+func (z zsh) Install(cmd, bin string) error {
+	if z.IsInstalled(cmd, bin) {
 		return fmt.Errorf("already installed in %s", z.rc)
 	}
 
+	completeCmd := z.cmd(cmd, bin)
 	bashCompInit := "autoload -U +X bashcompinit && bashcompinit"
 	if !lineInFile(z.rc, bashCompInit) {
 		completeCmd = bashCompInit + "\n" + completeCmd
@@ -26,11 +31,11 @@ func (z zsh) Install(cmd, bin string) error {
 }
 
 func (z zsh) Uninstall(cmd, bin string) error {
-	completeCmd := z.cmd(cmd, bin)
-	if !lineInFile(z.rc, completeCmd) {
+	if !z.IsInstalled(cmd, bin) {
 		return fmt.Errorf("does not installed in %s", z.rc)
 	}
 
+	completeCmd := z.cmd(cmd, bin)
 	return removeFromFile(z.rc, completeCmd)
 }