refactor: move apps listing from common plugin to apps plugin

This helps centralize app-related listing fetching.

plugins/apps/apps.go

@@ -1,5 +1,13 @@
 package apps
 
+import (
+	"fmt"
+	"io/ioutil"
+	"strings"
+
+	"github.com/dokku/dokku/plugins/common"
+)
+
 var (
 	// DefaultProperties is a map of all valid network properties with corresponding default property values
 	DefaultProperties = map[string]string{
@@ -13,3 +21,30 @@ var (
 		"deploy-source-metadata": true,
 	}
 )
+
+// DokkuApps returns a list of all local apps
+func DokkuApps() ([]string, error) {
+	apps := []string{}
+	dokkuRoot := common.MustGetEnv("DOKKU_ROOT")
+	files, err := ioutil.ReadDir(dokkuRoot)
+	if err != nil {
+		return apps, fmt.Errorf("You haven't deployed any applications yet")
+	}
+
+	for _, f := range files {
+		appRoot := common.AppRoot(f.Name())
+		if !common.DirectoryExists(appRoot) {
+			continue
+		}
+		if strings.HasPrefix(f.Name(), ".") {
+			continue
+		}
+		apps = append(apps, f.Name())
+	}
+
+	if len(apps) == 0 {
+		return apps, fmt.Errorf("You haven't deployed any applications yet")
+	}
+
+	return apps, nil
+}