package main

import (
    "myapp/webserver/app/common"
    "github.com/golang/glog"
    "github.com/gorilla/mux"
    "encoding/json"
    "strconv"
    "flag"
    "fmt"
    "log"
    "net/http"
    "net/rpc"
    "time"
    "sync"
)

type RpcConnection struct {
    sync.Mutex
    rpcClient *rpc.Client
}

var dataHost *string // endpoint for cache frontend service
var browserCacheControl *int
var router *mux.Router
var rpcConnection RpcConnection

func RpcConnect() (err error) {
    rpcConnection.rpcClient, err = rpc.DialHTTP("tcp", *dataHost)
    return err
}

// http://stackoverflow.com/a/6391185/1162491
func RpcConnectionCheck(rpcCallError error) {
    var err error
    if rpcConnection.rpcClient == nil {
        log.Println("Restarting RPC Connection due to nil connection")
        err = RpcConnect()
    } else if rpcCallError == rpc.ErrShutdown || reflect.TypeOf(rpcCallError) == reflect.TypeOf((*rpc.ServerError)(nil)).Elem() {
        log.Println("Restarting RPC Connection due to error")
        rpcConnection.Lock()
        err = RpcConnect()
        rpcConnection.Unlock()
    }

    if err != nil {
        log.Fatal("Unable to initialize connection to RPC")
    }
}

func HttpInterceptor(w http.ResponseWriter, r *http.Request) {
    startTime := time.Now()

    router.ServeHTTP(w, r)

    finishTime := time.Now()
    elapsedTime := finishTime.Sub(startTime)

    common.LogAccess(w, r, elapsedTime)
}

func main() {
    dataHost = flag.String("dl", "localhost:9001", "dataaccess endpoint")

    flag.Parse()
    defer glog.Flush()
    
    err := RpcConnect() 
    if err != nil {
        log.Fatal("Unable to initialize connection to RPC")
    }
    
    router = mux.NewRouter()

    router.HandleFunc("/healthcheck", func(w http.ResponseWriter, r *http.Request) {
        accessCall := rpcConnection.rpcClient.Go(...)
        replyCall := <-accessCall.Done

        if replyCall.Error != nil {
            http.Error(w, replyCall.Error.Error(), http.StatusInternalServerError)
            // Return the error no matter what - you could write your own reattempt loop and try here
            RpcConnectionCheck(replyCall.Error)
            return
        }
        fmt.Fprintf(w, "success")
    })
    
    http.HandleFunc("/", HttpInterceptor)
    http.ListenAndServe("0.0.0.0:"+*port, nil)
}