// Copyright 2017 Google Inc. All rights reserved.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to writing, software distributed
// under the License is distributed on a "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied.
//
// See the License for the specific language governing permissions and
// limitations under the License.

package main

import (
	"fmt"
	"log"
	"net/http"
	"strconv"
)

func main() {
	err := http.ListenAndServe(":8080", handler())
	if err != nil {
		log.Fatal(err)
	}
}

func handler() http.Handler {
	r := http.NewServeMux()
	r.HandleFunc("/double", doubleHandler)
	return r
}

func doubleHandler(w http.ResponseWriter, r *http.Request) {
	text := r.FormValue("v")
	if text == "" {
		http.Error(w, "missing value", http.StatusBadRequest)
		return
	}

	v, err := strconv.Atoi(text)
	if err != nil {
		http.Error(w, "not a number: "+text, http.StatusBadRequest)
		return
	}

	fmt.Fprintln(w, v*2)
}
