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package service
import (
"fmt"
"reflect"
)
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()) && e.hasStatus(StatusOK) {
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
}
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