package main

import (
	"fmt"
	"net/http"
	"os"
	"plugin"

	"github.com/fission/fission/environments/go/context"
)

const (
	CODE_PATH = "/userfunc/user"
)

var userFunc http.HandlerFunc

func loadPlugin() http.HandlerFunc {
	p, err := plugin.Open(CODE_PATH)
	if err != nil {
		panic(err)
	}
	sym, err := p.Lookup("Handler")
	if err != nil {
		panic("Entry point not found")
	}

	switch h := sym.(type) {
	case *http.Handler:
		return (*h).ServeHTTP
	case *http.HandlerFunc:
		return *h
	case func(http.ResponseWriter, *http.Request):
		return h
	case func(context.Context, http.ResponseWriter, *http.Request):
		return func(w http.ResponseWriter, r *http.Request) {
			c := context.New()
			h(c, w, r)
		}
	default:
		panic("Entry point not found: bad type")
	}
}

func specializeHandler(w http.ResponseWriter, r *http.Request) {
	if userFunc != nil {
		w.WriteHeader(400)
		w.Write([]byte("Not a generic container"))
		return
	}

	_, err := os.Stat(CODE_PATH)
	if err != nil {
		if os.IsNotExist(err) {
			w.WriteHeader(http.StatusNotFound)
			w.Write([]byte(CODE_PATH + ": not found"))
			return
		} else {
			panic(err)
		}
	}

	fmt.Println("Specializing ...")
	userFunc = loadPlugin()
	fmt.Println("Done")
}

func main() {
	http.HandleFunc("/specialize", specializeHandler)

	// Generic route -- all http requests go to the user function.
	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if userFunc == nil {
			w.WriteHeader(http.StatusInternalServerError)
			w.Write([]byte("Generic container: no requests supported"))
			return
		}
		userFunc(w, r)
	})

	fmt.Println("Listening on 8888 ...")
	http.ListenAndServe(":8888", nil)
}