add migration type

migration.go

@@ -0,0 +1,66 @@
+package version
+
+import (
+	"sort"
+)
+
+// Migration maps provide a simple way to run functions wrapped in version constraints.
+type Migration map[string]func() error
+
+// AllVersions returns a List of all versions in the migration map.
+func (m Migration) AllVersions() (List, error) {
+	l := List{}
+	for str := range m {
+		v, err := Parse(str)
+		if err != nil {
+			return nil, err
+		}
+
+		l = append(l, v)
+	}
+
+	sort.Stable(l)
+
+	return l, nil
+}
+
+// RequiredVersions returns a List of all versions in the migration map that are newer than a given (presumed current) version.
+// If currentVersion is nil, this is identical to AllVersions.
+func (m Migration) RequiredVersions(currentVersion *Version) (List, error) {
+	l, err := m.AllVersions()
+	if err != nil {
+		return nil, err
+	}
+
+	if currentVersion != nil {
+		c := &Constraint{
+			Gt: currentVersion,
+		}
+		l = l.Match(c)
+	}
+
+	return l, nil
+}
+
+// Run all required migration functions in the migration map.
+// If currentVersion is nil, all migrations will be run.
+// If afterEachCallback is not nil, it will be called after each successful migration.
+func (m Migration) Run(currentVersion *Version, afterEachCallback func(*Version)) error {
+	versions, err := m.RequiredVersions(currentVersion)
+	if err != nil {
+		return err
+	}
+
+	for _, v := range versions {
+		f := m[v.Text]
+		if err := f(); err != nil {
+			return err
+		}
+
+		if afterEachCallback != nil {
+			afterEachCallback(v)
+		}
+	}
+
+	return nil
+}