package network

import (
	//Builtin
	"errors"
	"fmt"
	"math/rand"
	"os"
	"time"

	// Internal
	"github.com/op/go-logging"
	
	//External
	"github.com/j-keck/arping"
	"github.com/milosgajdos83/tenus"
)

// Setup the networking inside the child
// Namely setup the loopback interface
// and the veth interface if requested
func NetSetup(stn *SandboxNetwork) error {
	if os.Getpid() != 1 {
		panic(errors.New("Cannot use NetSetip from parent."))
	}

	if err := setupLoopback(stn); err != nil {
		return fmt.Errorf("Unable to setup loopback interface: %+v", err)
	}

	// If required configure veth
	if stn.VethGuest != "" {
		if err := setupVEth(stn); err != nil {
			return fmt.Errorf("Unable to setup veth interface: %+v", err)
		}
	}

	return nil
}

func setupLoopback(stn *SandboxNetwork) error {
	// Bring loopback interface up
	lo, err := tenus.NewLinkFrom("lo")
	if err != nil {
		return fmt.Errorf("Unable to fetch loopback interface, %s.", err)
	}

	// Bring the link up
	err = lo.SetLinkUp()
	if err != nil {
		return fmt.Errorf("Unable to bring loopback interface up, %s.", err)
	}
	
	return nil
}

func setupVEth(stn *SandboxNetwork) error {
	ifc, err := tenus.NewLinkFrom(stn.VethGuest)
	
	if err != nil {
		return fmt.Errorf("Unable to fetch inteface %s, %s.", stn.VethGuest, err)
	}
	
	// Bring the link down to prepare for renaming
	if err = ifc.SetLinkDown(); err != nil {
		return fmt.Errorf("Unable to bring interface %s down, %s.", stn.VethGuest, err)
	}

	// Rename the interface to a standard eth0 (not really a necessity)
	if err = tenus.RenameInterface(stn.VethGuest, ozDefaultInterfaceInternal); err != nil {
		return fmt.Errorf("Unable to rename interface %s, %s.", stn.VethGuest, err)
	}

	// Refetch the interface again as it has changed
	ifc, err = tenus.NewLinkFrom(ozDefaultInterfaceInternal)
	if err != nil {
		return fmt.Errorf("Unable to fetch interface %s, %s.", ozDefaultInterfaceInternal, err)
	}

	// Bring the link back up
	if err = ifc.SetLinkUp(); err != nil {
		return fmt.Errorf("Unable to bring interface %s up, %s.", ozDefaultInterfaceInternal, err)
	}

	// Set the link's default gateway
	if err = ifc.SetLinkDefaultGw(&stn.Gateway); err != nil {
		return fmt.Errorf("Unable to set default route %s.", err)
	}
	
	return nil
}

// Try to find an unassigned IP address
// Do this by first trying two random IPs or, if that fails, sequentially
func getFreshIP(min, max uint64, log *logging.Logger) string {
	var newIP string

	for i := 0; i < ozMaxRandTries; i++ {
		newIP = getRandIP(min, max)
		if newIP != "" {
			break
		}
	}

	if newIP == "" {
		log.Notice("Random IP lookup failed %d times, reverting to sequential select", ozMaxRandTries)

		newIP = getScanIP(min, max)
	}

	return newIP

}

// Generate a random ip and arping it to see if it is available
// Returns the ip on success or an ip string is the ip is already taken
func getRandIP(min, max uint64) string {
	if min > max {
		return ""
	}

	dstIP := inet_ntoa(uint64(rand.Int63n(int64(max-min))) + min)

	arping.SetTimeout(time.Millisecond * 150)

	_, _, err := arping.PingOverIfaceByName(dstIP, ozDefaultInterfaceBridge)

	if err == arping.ErrTimeout {
		return dstIP.String()
	} else if err != nil {
		return dstIP.String()
	}

	return ""

}

// Go through all possible ips between min and max
// and arping each one until a free one is found
func getScanIP(min, max uint64) string {
	if min > max {
		return ""
	}

	for i := min; i < max; i++ {
		dstIP := inet_ntoa(i)

		arping.SetTimeout(time.Millisecond * 150)

		_, _, err := arping.PingOverIfaceByName(dstIP, ozDefaultInterfaceBridge)

		if err == arping.ErrTimeout {
			return dstIP.String()
		} else if err != nil {
			return dstIP.String()
		}
	}

	return ""

}