/*
Copyright 2016 The Kubernetes Authors 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 in writing, software
distributed under the License is distributed on an "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 kube

import (
	"fmt"
	"io"
	"io/ioutil"
	"net"
	"strconv"

	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/portforward"
	"k8s.io/client-go/tools/remotecommand"
)

// Tunnel describes a ssh-like tunnel to a kubernetes pod
type Tunnel struct {
	Local     int
	Remote    int
	Namespace string
	PodName   string
	Out       io.Writer
	stopChan  chan struct{}
	readyChan chan struct{}
	config    *rest.Config
	client    rest.Interface
}

// NewTunnel creates a new tunnel
func NewTunnel(client rest.Interface, config *rest.Config, namespace, podName string, remote int) *Tunnel {
	return &Tunnel{
		config:    config,
		client:    client,
		Namespace: namespace,
		PodName:   podName,
		Remote:    remote,
		stopChan:  make(chan struct{}, 1),
		readyChan: make(chan struct{}, 1),
		Out:       ioutil.Discard,
	}
}

// Close disconnects a tunnel connection
func (t *Tunnel) Close() {
	close(t.stopChan)
	close(t.readyChan)
}

// ForwardPort opens a tunnel to a kubernetes pod
func (t *Tunnel) ForwardPort() error {
	// Build a url to the portforward endpoint
	// example: http://localhost:8080/api/v1/namespaces/helm/pods/tiller-deploy-9itlq/portforward
	u := t.client.Post().
		Resource("pods").
		Namespace(t.Namespace).
		Name(t.PodName).
		SubResource("portforward").URL()

	dialer, err := remotecommand.NewExecutor(t.config, "POST", u)
	if err != nil {
		return err
	}

	local, err := getAvailablePort()
	if err != nil {
		return fmt.Errorf("could not find an available port: %s", err)
	}
	t.Local = local

	ports := []string{fmt.Sprintf("%d:%d", t.Local, t.Remote)}

	pf, err := portforward.New(dialer, ports, t.stopChan, t.readyChan, t.Out, t.Out)
	if err != nil {
		return err
	}

	errChan := make(chan error)
	go func() {
		errChan <- pf.ForwardPorts()
	}()

	select {
	case err = <-errChan:
		return fmt.Errorf("forwarding ports: %v", err)
	case <-pf.Ready:
		return nil
	}
}

func getAvailablePort() (int, error) {
	l, err := net.Listen("tcp", ":0")
	if err != nil {
		return 0, err
	}
	defer l.Close()

	_, p, err := net.SplitHostPort(l.Addr().String())
	if err != nil {
		return 0, err
	}
	port, err := strconv.Atoi(p)
	if err != nil {
		return 0, err
	}
	return port, err
}