package main

import (
  "fmt"
  "net/http"
  "html/template"
  "os"
  "os/exec"
  "regexp"
  "strconv"
  "bytes"
  "encoding/json"
)

var indexTemplate = template.Must(template.ParseFiles("html/index.html"))
var nodeList = []string{"higgsboson.vpn","turingmachine.vpn"}

func stringInSlice(a string, list []string) bool {
  for _,  b := range list {
    if b == a {
      return true
    }
  }
  return false
}

type IndexPage struct {
  Title string
  Nodes []string
}

type Status int

const (
  On Status = iota
  Off
  Slow
)

func indexHandler(w http.ResponseWriter, r *http.Request) {
  indexTemplate.Execute(w, &IndexPage{Title: "VPN Node Status", Nodes: nodeList})
}

func ping(node string) (int64) {
  cmd := exec.Command("fping", "-e", node)
  var out bytes.Buffer
  cmd.Stdout = &out
  err := cmd.Run()
  if err == nil {
    match := regexp.MustCompile("\\d+").Find(out.Bytes())
    if (match != nil) {
      time, _ := strconv.ParseInt(string(match), 10, 0);
      return time;
    }
    return -1
  } else {
    return -1
  }
}

type NodeStatus struct {
  Domain string
  Status string
  Ping int64
}

const lenPath = len("/status/")
func statusHandler(w http.ResponseWriter, r *http.Request) {
  node := r.URL.Path[lenPath:];
  if ! stringInSlice(node, nodeList) {
    w.WriteHeader(http.StatusNotFound)
  } else {
    var state string
    elapsed := ping(node);
    if elapsed == -1 {
      state = "DOWN"
    } else if elapsed > 200 {
      state = "SLOW"
    } else {
      state = "UP"
    }
    status := &NodeStatus{Domain: node, Status: state, Ping: elapsed}
    s, err := json.Marshal(status)
    if err != nil {
      w.WriteHeader(http.StatusInternalServerError)
      fmt.Printf("error while serializing json %s", err)
    } else {
      w.Write(s)
    }
  }
}

func main() {
  config, err := os.Open("./nodes.json")
  if err != nil {
    fmt.Printf("Cannot open nodes.json: '%s'", err)
    os.Exit(1);
  }
  jsonParser := json.NewDecoder(config)

  if err = jsonParser.Decode(&nodeList); err != nil {
    fmt.Printf("parsing config file: '%s'", err.Error())
    os.Exit(1);
  }

  http.HandleFunc("/status/", statusHandler)
  http.Handle("/assets/", http.StripPrefix("/assets", http.FileServer(http.Dir("./assets/"))))
  http.HandleFunc("/", indexHandler)
  fmt.Printf("Running on http://0.0.0.0:8080\n")
  http.ListenAndServe(":8080", nil)
}