1 files changed, 112 insertions, 0 deletions
diff --git a/service/injector.go b/service/injector.go
new file mode 100644
index 00000000..e7dfaa0b
--- /dev/null
+++ b/service/injector.go
@@ -0,0 +1,112 @@
+package service
+
+import (
+	"reflect"
+	"fmt"
+)
+
+const initMethod = "Init"
+
+var noConfig = fmt.Errorf("no config has been provided")
+
+// calls Init method with automatically resolved arguments.
+func initService(s interface{}, cfg Config, c *container) (bool, error) {
+	r := reflect.TypeOf(s)
+
+	m, ok := r.MethodByName(initMethod)
+	if !ok {
+		// no Init method is presented, assuming service does not need
+		// initialization.
+		return false, nil
+	}
+
+	if err := verifySignature(m); err != nil {
+		return false, err
+	}
+
+	// hydrating
+	values, err := injectValues(m, s, cfg, c)
+	if err != nil {
+		return false, err
+	}
+
+	// initiating service
+	out := m.Func.Call(values)
+
+	if out[1].IsNil() {
+		return out[0].Bool(), nil
+	}
+
+	return out[0].Bool(), out[1].Interface().(error)
+}
+
+// injectValues returns slice of call arguments for service Init method.
+func injectValues(m reflect.Method, s interface{}, cfg Config, c *container) (values []reflect.Value, err error) {
+	for i := 0; i < m.Type.NumIn(); i ++ {
+		v := m.Type.In(i)
+
+		switch {
+		case v.ConvertibleTo(reflect.ValueOf(s).Type()): // service itself
+			values = append(values, reflect.ValueOf(s))
+
+		case v.Implements(reflect.TypeOf((*HydrateConfig)(nil)).Elem()): // automatically configured config
+			if cfg == nil {
+				// todo: generic value
+				return nil, noConfig
+			}
+
+			sc := reflect.New(v.Elem())
+			if err := sc.Interface().(HydrateConfig).Hydrate(cfg); err != nil {
+				return nil, err
+			}
+
+			values = append(values, sc)
+
+		case v.Implements(reflect.TypeOf((*Config)(nil)).Elem()): // config section
+			if cfg == nil {
+				// todo: generic value
+				return nil, noConfig
+			}
+			values = append(values, reflect.ValueOf(cfg))
+
+		case v.Implements(reflect.TypeOf((*Container)(nil)).Elem()): // container
+			values = append(values, reflect.ValueOf(c))
+
+		default:
+			found := false
+
+			// looking for the service candidate
+			for _, e := range c.services {
+				if v.ConvertibleTo(reflect.ValueOf(e.svc).Type()) {
+					found = true
+					values = append(values, reflect.ValueOf(e.svc))
+					break
+				}
+			}
+
+			if !found {
+				// placeholder (make sure to check inside the method)
+				values = append(values, reflect.New(v).Elem())
+			}
+		}
+	}
+
+	return
+}
+
+// verifySignature checks if Init method has valid signature
+func verifySignature(m reflect.Method) error {
+	if m.Type.NumOut() != 2 {
+		return fmt.Errorf("method Init must have exact 2 return values")
+	}
+
+	if m.Type.Out(0).Kind() != reflect.Bool {
+		return fmt.Errorf("first return value of Init method must be bool type")
+	}
+
+	if !m.Type.Out(1).Implements(reflect.TypeOf((*error)(nil)).Elem()) {
+		return fmt.Errorf("second return value of Init method value must be error type")
+	}
+
+	return nil
+}