lazyhandler/magic/extractors.go

package magic

import (
	"log/slog"
	"net/http"
	"reflect"

	"git.jeffthecoder.xyz/public/lazyhandler/util"
)

var (
	extractors = make(map[reflect.Type]func(*http.Request) (any, error))

	extractorsTakesResponseWriter = make(map[reflect.Type]func(http.ResponseWriter, *http.Request) (any, error))
)

type FromRequest interface {
	FromRequest(*http.Request) error
}

type TakeResponseWriter interface {
	TakeResponseWriter(http.ResponseWriter)
}

func RegisterExtractor(o any, extractor func(*http.Request) (any, error)) {
	if t, ok := o.(reflect.Type); ok {
		slog.With("type", t.String()).Debug("extractor type registered with reflect.Type")
		extractors[t] = extractor
	} else if v, ok := o.(reflect.Value); ok {
		slog.With("type", v.Type().String(), "value", v.Interface()).Debug("extractor type registered with reflect.Value")

		extractors[v.Type()] = extractor
	} else {
		t := reflect.TypeOf(o)
		slog.With("type", t.String(), "value", o).Debug("extractor type registered with object")

		extractors[t] = extractor
	}
}

func RegisterExtractorGeneric[T any](extractor func(*http.Request) (any, error)) {
	var pointerToT *T
	RegisterExtractor(reflect.TypeOf(pointerToT).Elem(), extractor)
}

func RegisterExtractorThatTakesResponseWriter(o any, extractor func(http.ResponseWriter, *http.Request) (any, error)) {
	if t, ok := o.(reflect.Type); ok {
		slog.With("type", t.String()).Debug("extractor type registered with reflect.Type")
		extractorsTakesResponseWriter[t] = extractor
	} else if v, ok := o.(reflect.Value); ok {
		slog.With("type", v.Type().String(), "value", v.Interface()).Debug("extractor type registered with reflect.Value")

		extractorsTakesResponseWriter[v.Type()] = extractor
	} else {
		t := reflect.TypeOf(o)
		slog.With("type", t.String(), "value", o).Debug("extractor type registered with object")

		extractorsTakesResponseWriter[t] = extractor
	}
}

func RegisterExtractorThatTakesResponseWriterGeneric[T any](extractor func(http.ResponseWriter, *http.Request) (any, error)) {
	var pointerToT *T
	RegisterExtractorThatTakesResponseWriter(reflect.TypeOf(pointerToT).Elem(), extractor)
}

func GetExtractor(t reflect.Type) (func(http.ResponseWriter, *http.Request) (any, error), bool) {
	_, isTakeResponseWriter := util.Implements[TakeResponseWriter](t)
	if t.Kind() == reflect.Pointer {
		_, ptrIsTakeResponseWriter := util.Implements[TakeResponseWriter](t.Elem())
		isTakeResponseWriter = isTakeResponseWriter || ptrIsTakeResponseWriter
	}
	if _, ok := util.Implements[FromRequest](t); ok {
		if t.Kind() == reflect.Pointer {
			// T.Implement(FromRequest) and T is  Pointer
			// create new actual T and call T.FromRequest on it
			// if error happens, no error is returned. just return nil
			return func(w http.ResponseWriter, r *http.Request) (any, error) {
				// var t T
				// return t, t.FromRequest(r)
				z := reflect.New(t.Elem())

				if isTakeResponseWriter {
					z.MethodByName("TakeResponseWriter").Call([]reflect.Value{reflect.ValueOf(w)})
				}

				results := z.MethodByName("FromRequest").Call([]reflect.Value{reflect.ValueOf(r)})
				if err, ok := results[0].Interface().(error); ok && err != nil {
					if errResponse, ok := err.(ErrorResponse); ok {
						return reflect.Zero(t).Interface(), errResponse
					}
					return reflect.Zero(t).Interface(), nil
				}
				return z.Interface(), nil
			}, isTakeResponseWriter
		}
		// T.Implement(FromRequest) and T is not Pointer
		// create zero T and call T.FromRequest directly on it
		return func(w http.ResponseWriter, r *http.Request) (any, error) {
			// var t T
			// return t, t.FromRequest(r)
			z := reflect.Zero(t)

			if isTakeResponseWriter {
				z.MethodByName("TakeResponseWriter").Call([]reflect.Value{reflect.ValueOf(w)})
			}

			results := z.MethodByName("FromRequest").Call([]reflect.Value{reflect.ValueOf(r)})
			if err, ok := results[0].Interface().(error); ok {
				return z.Interface(), err
			}
			return z.Interface(), nil
		}, isTakeResponseWriter
	} else if v, ok := util.PointerImplements[FromRequest](t); ok {
		return func(w http.ResponseWriter, r *http.Request) (any, error) {
			// var t T
			// return t, t.FromRequest(r)
			z := reflect.New(v.Type().Elem())

			if isTakeResponseWriter {
				z.MethodByName("TakeResponseWriter").Call([]reflect.Value{reflect.ValueOf(w)})
			}

			results := z.MethodByName("FromRequest").Call([]reflect.Value{reflect.ValueOf(r)})
			if err := results[0].Interface(); err == nil {
				return z.Elem().Interface(), nil
			}
			return z.Elem().Interface(), results[0].Interface().(error)
		}, isTakeResponseWriter
	}

	if extractor, ok := extractors[t]; ok {
		return func(_ http.ResponseWriter, r *http.Request) (any, error) {
			return extractor(r)
		}, false
	}

	if t.Kind() == reflect.Pointer {
		if extractor, ok := extractors[t.Elem()]; ok {
			return func(w http.ResponseWriter, r *http.Request) (any, error) {
				v, err := extractor(r)
				if err != nil {
					return nil, err
				}
				return &v, nil
			}, false
		}
	}

	if extractor, ok := extractorsTakesResponseWriter[t]; ok {
		return func(w http.ResponseWriter, r *http.Request) (any, error) {
			return extractor(w, r)
		}, true
	}

	if t.Kind() == reflect.Pointer {
		if extractor, ok := extractorsTakesResponseWriter[t.Elem()]; ok {
			return func(w http.ResponseWriter, r *http.Request) (any, error) {
				v, err := extractor(w, r)
				if err != nil {
					return nil, err
				}
				return &v, nil
			}, true
		}
	}

	return nil, isTakeResponseWriter
}