package main 
import (
    "net/http"
)
 
func HelloResponse(rw http.ResponseWriter, request *http.Request) {
    fmt.Fprintf(w, "Hello world.")
}
 
func main() {
    http.HandleFunc("/", HelloResponse)
    http.ListenAndServe(":3000", nil)
}

type IndexController struct {
}
 
func (IndexController *IndexController) Index(//params) (//return values) {
}

http.HandleFunc(path, HandleRequest()) 
func HandleRequest() {
    return func(rw http.ResponseWriter, request *http.Request) {
        // do your logic
    }
}

package main 
import (
    "net/url"
    "net/http"
    "github.com/ZhenhangTung/GoGym"
)
 
type IndexController struct {
}
 
func (IndexController *IndexController) Index(request map[string]url.Values, headers http.Header) (statusCode int, response interface{}) {
    return 200, map[string]string{"hello": "world"}
}
 
type BarController struct {
}
 
func (*BarController) Bar(request map[string]url.Values, headers http.Header) (statusCode int, response interface{}, responseHeader http.Header) {
    return 200, map[string]string{"GoTo": "Bar"}, http.Header{"Foo": {"Bar", "Baz"}}
}
 
func main() {
    var apiService = GoGym.Prepare()
    apiService.Get("index", "IndexController@Index")
    apiService.Post("bar", "BarController@Bar")
    controllers := []interface{}{&IndexController{}}
    apiService.RegisterControllers(controllers)
    apiService.RegisterController(&BarController{})
    apiService.Serve(3000)
}

package GoGym 
import (
    "encoding/json"
    "fmt"
    "net/http"
    "net/url"
    "reflect"
    "strings"
)
 
const (
    GETMethod     = "GET"
    POSTMethod    = "POST"
    PUTMethod     = "PUT"
    PATCHMethod   = "PATCH"
    DELETEMethod  = "DELETE"
    OPTIONSMethod = "OPTIONS"
)
 
const (
    HTTPMethodNotAllowed = 405
)
 
// APIService for now is the struct for containing controllerRegistry and registeredPathAndController,
// and it is the core service provider
type APIService struct {
    // controllerRegistry is where all registered controllers exist
    controllerRegistry map[string]interface{}
    //registeredPathAndController is a mapping of paths and controllers
    registeredPathAndController map[string]map[string]map[string]string
    requestForm                 map[string]url.Values
}
 
func (api *APIService) Get(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(GETMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Post(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(POSTMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Put(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(PUTMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Patch(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(PATCHMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Options(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(OPTIONSMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
func (api *APIService) Delete(path, controllerWithActionString string) {
    mapping := api.mappingRequestMethodWithControllerAndActions(DELETEMethod, path, controllerWithActionString)
    api.registeredPathAndController[path] = mapping
}
 
// mappingRequestMethodWithControllerAndActions is a function for mapping request method with controllers
// which containing actions
func (api *APIService) mappingRequestMethodWithControllerAndActions(requestMethod, path, controllerWithActionString string) map[string]map[string]string {
    mappingResult := make(map[string]map[string]string)
    if length := len(api.registeredPathAndController[path]); length > 0 {
        mappingResult = api.registeredPathAndController[path]
    }
    controllerAndActionSlice := strings.Split(controllerWithActionString, "@")
    controller := controllerAndActionSlice[0]
    action := controllerAndActionSlice[1]
    controllerAndActionMap := map[string]string{controller: action}
    mappingResult[requestMethod] = controllerAndActionMap
    return mappingResult
}
 
// HandleRequest is a function to handle http request
func (api *APIService) HandleRequest(controllers map[string]map[string]string) http.HandlerFunc {
    return func(rw http.ResponseWriter, request *http.Request) {
        request.ParseForm()
        method := request.Method
        api.requestForm["query"] = request.Form
        api.requestForm["form"] = request.PostForm
        macthedControllers, ok := controllers[method]
        if !ok {
            rw.WriteHeader(HTTPMethodNotAllowed)
        }
        for k, v := range macthedControllers {
            controllerKey := "*" + k
            controller := api.controllerRegistry[controllerKey]
            in := make([]reflect.Value, 2)
            in[0] = reflect.ValueOf(api.requestForm)
            in[1] = reflect.ValueOf(request.Header)
            returnValues := reflect.ValueOf(controller).MethodByName(v).Call(in)
            statusCode := returnValues[0].Interface()
            intStatusCode := statusCode.(int)
            response := returnValues[1].Interface()
            responseHeaders := http.Header{}
            if len(returnValues) == 3 {
                responseHeaders = returnValues[2].Interface().(http.Header)
            }
            api.JSONResponse(rw, intStatusCode, response, responseHeaders)
        }
    }
}
 
// RegisterHandleFunc is a function registers a handle function to handle request from path
func (api *APIService) RegisterHandleFunc() {
    for k, v := range api.registeredPathAndController {
        path := k
        if !strings.HasPrefix(k, "/") {
            path = fmt.Sprintf("/%v", k)
        }
        http.HandleFunc(path, api.HandleRequest(v))
    }
}
 
// RegisterControllers is a function registers a struct of controllers into controllerRegistry
func (api *APIService) RegisterControllers(controllers []interface{}) {
    for _, v := range controllers {
        api.RegisterController(v)
    }
}
 
// RegisterControllers is a function registers a controller into controllerRegistry
func (api *APIService) RegisterController(controller interface{}) {
    controllerType := getType(controller)
    api.controllerRegistry[controllerType] = controller
}
 
// getType is a function gets the type of value
func getType(value interface{}) string {
    if t := reflect.TypeOf(value); t.Kind() == reflect.Ptr {
        return "*" + t.Elem().Name()
    } else {
        return t.Name()
    }
}
 
// Serve is a function
func (api *APIService) Serve(port int) {
    api.RegisterHandleFunc()
    fullPort := fmt.Sprintf(":%d", port)
    http.ListenAndServe(fullPort, nil)
}
 
// JSONResponse is a function return json response
func (api *APIService) JSONResponse(rw http.ResponseWriter, statusCode int, response interface{}, headers http.Header) {
    for k, v := range headers {
        for _, header := range v {
            rw.Header().Add(k, header)
        }
    }
    rw.Header().Add("Content-Type", "application/json")
    rw.WriteHeader(statusCode)
    rsp, err := json.Marshal(response)
    if err != nil {
        // TODO: logging error
        fmt.Println("JSON err:", err)
    }
    rw.Write(rsp)
}
 
// Prepare is a fucntion prepare the service and return prepared service to the user
func Prepare() *APIService {
    var apiService = new(APIService)
    apiService.controllerRegistry = make(map[string]interface{})
    apiService.registeredPathAndController = make(map[string]map[string]map[string]string)
    apiService.requestForm = make(map[string]url.Values)
    return apiService
}