package router

import (
	"fmt"
	"net/http"
	"strings"
)

type Router struct {
	*http.ServeMux
	routes         map[string]http.Handler
	requiredRoutes []string
}

func NewRouter(mux *http.ServeMux, requiredRoutes ...string) (ro *Router) {
	if mux == nil {
		mux = http.NewServeMux()
	}
	ro = &Router{
		ServeMux:       mux,
		routes:         make(map[string]http.Handler),
		requiredRoutes: make([]string, 0),
	}
	ro.AddRequiredRoutes(requiredRoutes...)
	return
}

func (ro *Router) AddRequiredRoutes(requiredRoutes ...string) {
	if requiredRoutes == nil {
		return
	}
	ro.requiredRoutes = append(ro.requiredRoutes, requiredRoutes...)
}

func (ro *Router) Register(pattern string, server http.Handler) (err error) {
	if !strings.HasPrefix(pattern, "/") {
		return fmt.Errorf("missing preceding slash in pattern (%s)", pattern)
	}
	if server == nil {
		return fmt.Errorf("server must be provided")
	}
	srv, exists := ro.routes[pattern]
	if exists && srv != nil {
		return fmt.Errorf("too many routes for same pattern (%s)", pattern)
	}
	ro.routes[pattern] = server
	ro.ServeMux.Handle(string(pattern), ro.routes[pattern])
	return
}

func (ro *Router) Validate() (err error) {
	for _, requiredRoute := range ro.requiredRoutes {
		_, ok := ro.routes[requiredRoute]
		if !ok {
			err = fmt.Errorf("missing required route (%s)", requiredRoute)
			return
		}
	}
	return
}

func (ro *Router) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if err := ro.Validate(); err != nil {
		panic(err)
	}
	ro.ServeMux.ServeHTTP(w, r)
}