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mediatr.go
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mediatr.go
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package mediatr
import (
"context"
"errors"
"fmt"
"reflect"
)
var (
requests = map[reflect.Type]any{}
pipeline Middleware
)
type Request[T any] interface {
Request(T)
}
type RequestHandler[R Request[T], T any] interface {
Handle(context.Context, R) (T, error)
}
func RegisterRequestHandler[R Request[T], T any](rh RequestHandler[R, T]) error {
var (
req R
rt = reflect.TypeOf(req)
)
_, exists := requests[rt]
if exists {
return fmt.Errorf("handler for request %T already exists", req)
}
requests[rt] = rh
return nil
}
type RequestHandlerFunc[R Request[T], T any] func(context.Context, R) (T, error)
func (f RequestHandlerFunc[R, T]) Handle(ctx context.Context, req R) (T, error) {
return f(ctx, req)
}
func RegisterHandlerFunc[R Request[T], T any](f func(context.Context, R) (T, error)) error {
return RegisterRequestHandler(RequestHandlerFunc[R, T](f))
}
type MiddlewareHandler interface {
Handle(context.Context, any) (any, error)
}
type MiddlewareFunc func(context.Context, any) (any, error)
func (f MiddlewareFunc) Handle(ctx context.Context, req any) (any, error) {
return f(ctx, req)
}
type Middleware func(MiddlewareFunc) MiddlewareFunc
func RegisterMiddleware(mw ...Middleware) {
pipeline = func(outer Middleware, others ...Middleware) Middleware {
return func(next MiddlewareFunc) MiddlewareFunc {
for i := len(others) - 1; i >= 0; i-- { // reverse
next = others[i](next)
}
if outer == nil {
return next
}
return outer(next)
}
}(pipeline, mw...)
}
func Send[R Request[T], T any](ctx context.Context, req R) (T, error) {
handler, ok := requests[reflect.TypeOf(req)]
if !ok {
return *new(T), fmt.Errorf("no handler for request %T", req)
}
rh, ok := handler.(RequestHandler[R, T])
if !ok {
return *new(T), fmt.Errorf("handler for request %T is not a Handler", req)
}
if pipeline == nil {
return rh.Handle(ctx, req)
}
fn := func(ctx context.Context, req any) (res any, err error) {
return rh.Handle(ctx, req.(R))
}
res, err := pipeline(fn)(ctx, req)
if err != nil {
return *new(T), err
}
return res.(T), nil
}
func ClearRequestRegistrations() {
requests = map[reflect.Type]any{}
}
type NotificationHandlerFunc[T any] func(ctx context.Context, event T) error
var notifications = map[reflect.Type][]any{}
// RegisterNotificationHandler register the notification handler to mediatr registry.
func RegisterNotificationHandler[T any](handler NotificationHandlerFunc[T]) error {
var event T
eventType := reflect.TypeOf(event)
handlers, exist := notifications[eventType]
if !exist {
notifications[eventType] = []any{handler}
return nil
}
notifications[eventType] = append(handlers, handler)
return nil
}
// RegisterNotificationHandlers register the notification handlers to mediatr registry.
func RegisterNotificationHandlers[T any](handlers ...NotificationHandlerFunc[T]) error {
if len(handlers) == 0 {
return errors.New("no handlers provided")
}
for _, handler := range handlers {
err := RegisterNotificationHandler(handler)
if err != nil {
return err
}
}
return nil
}
// Publish the notification event to its corresponding notification handler.
func Publish[T any](ctx context.Context, event T) error {
handlers, ok := notifications[reflect.TypeOf(event)]
if !ok {
return nil
}
for _, handler := range handlers {
fn, ok := handler.(NotificationHandlerFunc[T])
if !ok {
return fmt.Errorf("handler for notification %T is not a Handler", event)
}
err := fn(ctx, event)
if err != nil {
return fmt.Errorf("error handling notification: %w", err)
}
}
return nil
}
func ClearNotificationRegistrations() {
notifications = map[reflect.Type][]any{}
}