farm: new package to handle set of cli contexts

Signed-off-by: Tibor Vass <tibor@docker.com>

farm/farm.go

@@ -0,0 +1,45 @@
+package farm
+
+import (
+	"os"
+	"path/filepath"
+)
+
+// Name of a Farm.
+type Name string
+
+// Context name of docker cli context.
+type Context string
+
+// Platform represents the platform OS/Architecture of a Context.
+type Platform string
+
+// Farm is a set of Context objects mapped to a Platform.
+// This could change in the future to be more generic.
+type Farm map[Platform]Context
+
+// Ville is a set of Farms.
+type Ville struct {
+	Farms map[Name]Farm
+	ActiveFarm Name
+}
+
+func LoadVille(root string) (*Ville, error) {
+	if err := os.MkdirAll(root, 0755); err != nil {
+		return err
+	}
+	v := &Ville{Farms: make(map[Name]Farm)}
+	err := filepath.Walk(root, func(p string, fi os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+		if p == root {
+			return nil
+		}
+		if fi.IsDir() {
+			return filepath.SkipDir
+		}
+		v.Farms[fi.Name()] = map[Platform]Context{}
+	})
+	return v, err
+}