internal/component: Further optimize initialization

internal/component/pool_meta.go

@@ -0,0 +1,126 @@
+package component
+
+import (
+	"reflect"
+	"sync"
+
+	"github.com/FAU-CDI/wisski-distillery/pkg/slicesx"
+	"github.com/tkw1536/goprogram/lib/reflectx"
+)
+
+//
+// META
+//
+
+var metaCache sync.Map
+
+// getMeta gets the component belonging to a component type
+func getMeta[C Component]() meta {
+	tp := reflectx.TypeOf[C]()
+
+	// we already have a m => return it
+	if m, ok := metaCache.Load(tp); ok {
+		return m.(meta)
+	}
+
+	// create a new m
+	var m meta
+	m.init(tp)
+
+	// store it in the cache
+	metaCache.Store(tp, m)
+	return m
+}
+
+// meta stores meta-information about a specific component
+type meta struct {
+	Name string       // the type name of this component
+	Elem reflect.Type // the element type of the component
+
+	CFields map[string]reflect.Type // fields with type C for which C implements component
+	IFields map[string]reflect.Type // fields []I where I is an interface that implements component
+}
+
+// componentType is the type of components
+var componentType = reflectx.TypeOf[Component]()
+
+// init initializes this refklecttype
+func (m *meta) init(tp reflect.Type) {
+	if tp.Kind() != reflect.Pointer && tp.Elem().Kind() != reflect.Struct {
+		panic("GetMeta: Type (" + tp.String() + ") must be backed by a pointer to slice")
+	}
+
+	m.Name = tp.Elem().PkgPath() + "." + tp.Elem().Name()
+	m.Elem = tp.Elem()
+
+	m.CFields = make(map[string]reflect.Type)
+	m.IFields = make(map[string]reflect.Type)
+
+	// fill the above variables, with a mapping of field name to struct
+	count := m.Elem.NumField()
+	for i := 0; i < count; i++ {
+		field := m.Elem.Field(i)
+
+		name := field.Name
+		tp := field.Type
+
+		switch {
+		// field is a pointer to struct that implements a component
+		case tp.Implements(componentType) && tp.Kind() == reflect.Pointer && tp.Elem().Kind() == reflect.Struct:
+			m.CFields[name] = tp
+
+		// field is []I, where I is an interface that implements component
+		case tp.Kind() == reflect.Slice && tp.Elem().Kind() == reflect.Interface && tp.Elem().Implements(componentType):
+			m.IFields[name] = tp.Elem()
+		}
+	}
+}
+
+// New creates a new ComponentDescription
+func (m meta) New() Component {
+	return reflect.New(m.Elem).Interface().(Component)
+}
+
+// NeedsInitComponent
+func (m meta) NeedsInitComponent() bool {
+	return len(m.CFields) > 0 || len(m.IFields) > 0
+}
+
+// InitComponent sets up the fields of the given instance of a component.
+func (m meta) InitComponent(instance reflect.Value, all []Component) {
+	elem := instance.Elem()
+
+	// assign the component fields
+	for field, eType := range m.CFields {
+		c := slicesx.First(all, func(c Component) bool {
+			return reflect.TypeOf(c).AssignableTo(eType)
+		})
+
+		field := elem.FieldByName(field)
+		field.Set(reflect.ValueOf(c))
+	}
+
+	// assign the multi subtypes
+	registryR := reflect.ValueOf(all)
+	for field, eType := range m.IFields {
+		cs := filterSubtype(registryR, eType)
+		field := elem.FieldByName(field)
+		field.Set(cs)
+	}
+}
+
+// filterSubtype filters the slice of type []S into a slice of type []iface.
+// S and I must be interface types.
+func filterSubtype(sliceS reflect.Value, iface reflect.Type) reflect.Value {
+	len := sliceS.Len()
+
+	// convert each element
+	result := reflect.MakeSlice(reflect.SliceOf(iface), 0, len)
+	for i := 0; i < len; i++ {
+		element := sliceS.Index(i)
+		if element.Type().Implements(iface) {
+			result = reflect.Append(result, element.Elem().Convert(iface))
+		}
+	}
+	return result
+}