initial code (#6)

* initial code commit

nabarr.go

@@ -0,0 +1,48 @@
+package nabarr
+
+import (
+	"github.com/antonmedv/expr/vm"
+	"github.com/l3uddz/nabarr/media"
+	"time"
+)
+
+type ExprProgram struct {
+	expression string
+	Program    *vm.Program
+}
+
+func (p *ExprProgram) String() string {
+	return p.expression
+}
+
+func NewExprProgram(expression string, vm *vm.Program) *ExprProgram {
+	return &ExprProgram{
+		expression: expression,
+		Program:    vm,
+	}
+}
+
+type ExprEnv struct {
+	media.Item
+	Now func() time.Time
+}
+
+func NewExprEnv(media *media.Item) *ExprEnv {
+	return &ExprEnv{
+		Item: *media,
+		Now:  func() time.Time { return time.Now().UTC() },
+	}
+}
+
+func StringOrDefault(currentValue *string, defaultValue string) string {
+	if currentValue == nil {
+		return defaultValue
+	}
+	return *currentValue
+}
+func Uint64OrDefault(currentValue *uint64, defaultValue uint64) uint64 {
+	if currentValue == nil {
+		return defaultValue
+	}
+	return *currentValue
+}