/*

A trivial application to illustrate how the fdlib library can be used
in assignment 1 for UBC CS 416 2018W1.

Usage:
go run client.go
*/

package main

// Expects fdlib.go to be in the ./fdlib/ dir, relative to
// this client.go file
import "./fdlib"

import "fmt"
import "os"
import "time"

func main() {
    // Local (127.0.0.1) hardcoded IPs to simplify testing.
    localIpPort := "198.162.33.54:8080"
    toMonitorIpPort := "198.162.33.23:9999" // TODO: change this to remote node
    var lostMsgThresh uint8 = 5

    // TODO: generate a new random epoch nonce on each run
    var epochNonce uint64 = 0xffff
    var chCapacity uint8 = 5

    // Initialize fdlib. Note the use of multiple assignment:
    // https://gobyexample.com/multiple-return-values
    fd, notifyCh, err := fdlib.Initialize(epochNonce, chCapacity)
    if checkError(err) != nil {
        return
    }

    // Stop monitoring and stop responding on exit.
    // Defers are really cool, check out: https://blog.golang.org/defer-panic-and-recover
    defer fd.StopMonitoring()
    defer fd.StopResponding()

    err = fd.StartResponding(localIpPort)
    if checkError(err) != nil {
        return
    }

    fmt.Println("Started responding to heartbeats.")

    // Add a monitor for a remote node.
    localIpPortMon := "198.162.33.54:9999"
    err = fd.AddMonitor(localIpPortMon, toMonitorIpPort, lostMsgThresh)
    if checkError(err) != nil {
        return
    }

    fmt.Println("Started to monitor node: ", toMonitorIpPort)

    // Wait indefinitely, blocking on the notify channel, to detect a
    // failure.
    select {
    case notify := <-notifyCh:
        fmt.Println("Detected a failure of", notify)
        // Re-add the remote node for monitoring.
        err := fd.AddMonitor(localIpPortMon, toMonitorIpPort, lostMsgThresh)
        if checkError(err) != nil {
            return
        }
        fmt.Println("Started to monitor node: ", toMonitorIpPort)
    case <-time.After(time.Duration(int(lostMsgThresh)*3) * time.Second):
        // case <-time.After(time.Second):
        fmt.Println("No failures detected")
    }
}

// If error is non-nil, print it out and return it.
func checkError(err error) error {
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error ", err.Error())
        return err
    }
    return nil
}