Adds Available

this is the database for available packages

available.go

@@ -0,0 +1,40 @@
+package pm
+
+import (
+	"github.com/pkg/errors"
+)
+
+// Name exists to document the keys in Available
+type Name string
+
+// Version exists to document the keys in Available
+type Version string
+
+// Available is the structure used to represent the collection of all packages
+// that can be installed.
+type Available map[Name]map[Version]Meta
+
+// Add inserts m into a.
+func (a Available) Add(m Meta) error {
+	if _, err := m.Valid(); err != nil {
+		return errors.Wrap(err, "invalid meta")
+	}
+
+	if _, ok := a[Name(m.Name)]; !ok {
+		a[m.Name] = map[Version]Meta{}
+	}
+	a[m.Name][m.Version] = m
+	return nil
+}
+
+// Update inserts all data from o into a.
+func (a Available) Update(o Available) error {
+	for _, vers := range o {
+		for _, m := range vers {
+			if err := a.Add(m); err != nil {
+				return errors.Wrap(err, "adding")
+			}
+		}
+	}
+	return nil
+}