reflect.go

package neffos

import (
	"reflect"
	"strings"
)

func indirectType(typ reflect.Type) reflect.Type {
	if typ.Kind() == reflect.Ptr {
		typ = typ.Elem()
	}

	return typ
}

func isZero(v reflect.Value) bool {
	switch v.Kind() {
	case reflect.Struct:
		zero := true
		for i := 0; i < v.NumField(); i++ {
			zero = zero && isZero(v.Field(i))
		}

		if typ := v.Type(); typ != nil && v.IsValid() {
			f, ok := typ.MethodByName("IsZero")
			// if not found
			// if has input arguments (1 is for the value receiver, so > 1 for the actual input args)
			// if output argument is not boolean
			// then skip this IsZero user-defined function.
			if !ok || f.Type.NumIn() > 1 || f.Type.NumOut() != 1 && f.Type.Out(0).Kind() != reflect.Bool {
				return zero
			}

			method := v.Method(f.Index)
			// no needed check but:
			if method.IsValid() && !method.IsNil() {
				// it shouldn't panic here.
				zero = method.Call(nil)[0].Interface().(bool)
			}
		}

		return zero
	case reflect.Func, reflect.Map, reflect.Slice:
		return v.IsNil()
	case reflect.Array:
		zero := true
		for i := 0; i < v.Len(); i++ {
			zero = zero && isZero(v.Index(i))
		}
		return zero
	}
	// if not any special type then use the reflect's .Zero
	// usually for fields, but remember if it's boolean and it's false
	// then it's zero, even if set-ed.

	if !v.CanInterface() {
		// if can't interface, i.e return value from unexported field or method then return false
		return false
	}

	zero := reflect.Zero(v.Type())
	return v.Interface() == zero.Interface()
}

// does not support child elements on purpose.
func visitFields(typ reflect.Type, visitor func(f reflect.StructField) bool) int {
	typ = indirectType(typ)

	for n, i := typ.NumField(), 0; i < n; i++ {
		f := typ.Field(i)
		found := visitor(f)
		if found {
			return i
		}
	}

	return -1
}

func getNonZeroFields(v reflect.Value) (fields map[int]reflect.Value) {
	v = reflect.Indirect(v)

	visitFields(v.Type(), func(f reflect.StructField) bool {
		fieldIndex := f.Index[0]
		fieldValue := v.Field(fieldIndex)
		if !isZero(fieldValue) {
			if fields == nil {
				fields = make(map[int]reflect.Value)
			}

			fields[fieldIndex] = fieldValue
		}

		return false
	})

	return
}

func getFieldIndex(forType reflect.Type, fieldType reflect.Type) int {
	return visitFields(forType, func(f reflect.StructField) bool {
		return f.Type == fieldType
	})
}

func resolveStructNamespace(v reflect.Value) (string, bool) {
	// By Namespace() string method.
	typ := v.Type()
	method, ok := typ.MethodByName("Namespace")
	if ok {
		if getNamespace, ok := v.Method(method.Index).Interface().(func() string); ok {
			namespace := getNamespace()
			Debugf("Set namespace [\"%s\"] from method [%s.%s]", func() dargs {
				return dargs{namespace, nameOf(typ), method.Name}
			})

			return namespace, true
		}
	}

	// By field Namespace string with filled value.
	typ = indirectType(typ)
	v = reflect.Indirect(v)
	if f, ok := typ.FieldByNameFunc(func(s string) bool { return s == "Namespace" }); ok {
		if f.Type.Kind() == reflect.String {
			namespace := v.Field(f.Index[0]).String()
			Debugf("Set namespace [\"%s\"] from field [%s.%s]", func() dargs {
				return dargs{namespace, nameOf(typ), f.Name}
			})
			return namespace, true
		}
	}

	return "", false
}

var (
	nsConnType = reflect.TypeOf((*NSConn)(nil))
	msgType    = reflect.TypeOf(Message{})
	errType    = reflect.TypeOf((*error)(nil)).Elem()
)

func makeMessageHandlerFuncType(forType reflect.Type, nsConnFieldIndex int) reflect.Type {
	// Create the dynamic type which methods will be compared to.
	// remember, the receiver Ptr is also part of the input arguments,
	// that's why we don't use a static type assertion.
	expectedIn := []reflect.Type{
		forType,
		nsConnType,
		msgType,
	}

	if nsConnFieldIndex >= 0 {
		// Except when the Ptr is a dynamic one (has a field of NSConn) then the event callback does not require
		// that on its input arguments.
		expectedIn = append(expectedIn[0:1], expectedIn[2:]...)
	}

	return reflect.FuncOf(expectedIn, []reflect.Type{errType}, false)
}

func isArgOf(fnType reflect.Type, argType reflect.Type) bool {
	if fnType.Kind() != reflect.Func {
		panic("isArgOf used on a non-method type")
	}

	for i, n := 0, fnType.NumIn(); i < n; i++ {
		if fnType.In(i) == argType {
			return true
		}
	}

	return false
}

func makeEventFromMethod(v reflect.Value, method reflect.Method, eventMatcher EventMatcherFunc) (eventName string, cb MessageHandlerFunc) {
	eventName = method.Name

	// if method looks like a system event, i.e
	// OnNamespaceConnected, then convert its registered event name
	// _OnNamespaceConnected which is the correct.
	// We could accept a func like:
	// func(s *myConn) _OnNamespaceConnected(msg neffos.Message) error
	// but Go linting does not allow this and
	// we don't want our users to have yellow boxes everywhere in their editors.
	if IsSystemEvent("_" + eventName) {
		eventName = "_" + eventName
	}

	if !IsSystemEvent(eventName) {
		if eventMatcher != nil {
			newName, ok := eventMatcher(method.Name)
			if !ok {
				return "", nil
			}

			eventName = newName
		}
	}

	if isArgOf(method.Type, nsConnType) {
		// it should accept NSConn - static "controller".
		cb = v.Method(method.Index).Interface().(func(*NSConn, Message) error)
	} else {
		// the NSConn exists on the "controller" itself which is set dynamically.
		cb = func(c *NSConn, msg Message) error {
			// load an existing instance which contains the same "c".
			return c.value.Method(method.Index).Interface().(func(Message) error)(msg)
		}
	}

	return
}

// StructInjector is a type which injects a dynamic struct value.
// See `Struct.SetInjector` for more.
type StructInjector func(structType reflect.Type, nsConn *NSConn) (structValue reflect.Value)

func nameOf(structType reflect.Type) string {
	structType = indirectType(structType)

	typName := structType.Name()
	pkgPath := structType.PkgPath()
	fullname := pkgPath[strings.LastIndexByte(pkgPath, '/')+1:] + "." + typName
	return fullname
}

func makeEventsFromStruct(v reflect.Value, eventMatcher EventMatcherFunc, injector StructInjector) Events {
	events := make(Events)

	typ := v.Type()

	// get the index of field of a "NSConn" type.
	nsConnFieldIndex := getFieldIndex(typ, nsConnType)
	msgHandlerType := makeMessageHandlerFuncType(typ, nsConnFieldIndex)

	for i, n := 0, typ.NumMethod(); i < n; i++ {
		method := typ.Method(i)

		if method.Type != msgHandlerType {
			continue
		}

		eventName, cb := makeEventFromMethod(v, method, eventMatcher)
		if cb == nil {
			continue
		}

		Debugf("Event [\"%s\"] is handled by [%s.%s] method", func() dargs {
			return dargs{eventName, nameOf(typ), method.Name}
		})

		events[eventName] = cb
	}

	if nsConnFieldIndex != -1 {
		typ = indirectType(typ)

		var staticFields map[int]reflect.Value

		if injector == nil {
			// maybe this should be added no matter what, I have to check
			// some things in our company's production server first.
			staticFields = getNonZeroFields(v)

			DebugEach(staticFields, func(idx int, f reflect.Value) {
				fval := f.Interface()
				fname := typ.Field(idx).Name
				if fname == "Namespace" {
					// let's no log this as user field because
					// it's optionally used to provide a namespace on NewStruct.GetNamespaces().
					return
				}

				Debugf("Field [%s.%s] marked as static on value [%v]", nameOf(typ), fname, fval)
			})

			injector = func(typ reflect.Type, nsConn *NSConn) reflect.Value {
				return reflect.New(typ)
			}
		}

		cb, hasNamespaceConnect := events[OnNamespaceConnect]

		events[OnNamespaceConnect] = func(c *NSConn, msg Message) error {
			cachePtr := injector(typ, c)
			cacheElem := cachePtr.Elem()

			// set the NSConn dynamic field.
			cacheElem.Field(nsConnFieldIndex).Set(reflect.ValueOf(c))

			// set any static fields if default injector (see above).
			for findex, fvalue := range staticFields {
				cacheElem.Field(findex).Set(fvalue)
			}

			// Store it for the rest of the events inside
			// this namespace of that specific connection.
			c.value = cachePtr

			if hasNamespaceConnect {
				return cb(c, msg)
			}

			return nil
		}
	}

	return events
}