// Copyright 2015 flannel authors
//
// 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 subnet

import (
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"path"
	"regexp"
	"strconv"
	"sync"
	"time"

	etcd "github.com/coreos/flannel/Godeps/_workspace/src/github.com/coreos/etcd/client"
	"github.com/coreos/flannel/Godeps/_workspace/src/github.com/coreos/etcd/pkg/transport"
	log "github.com/coreos/flannel/Godeps/_workspace/src/github.com/golang/glog"
	"github.com/coreos/flannel/Godeps/_workspace/src/golang.org/x/net/context"

	"github.com/coreos/flannel/pkg/ip"
)

var (
	subnetRegex *regexp.Regexp = regexp.MustCompile(`(\d+\.\d+.\d+.\d+)-(\d+)`)
	ErrTryAgain                = errors.New("try again")
)

type Registry interface {
	getNetworkConfig(ctx context.Context, network string) (string, error)
	getSubnets(ctx context.Context, network string) ([]Lease, uint64, error)
	createSubnet(ctx context.Context, network string, sn ip.IP4Net, attrs *LeaseAttrs, ttl time.Duration) (time.Time, error)
	updateSubnet(ctx context.Context, network string, sn ip.IP4Net, attrs *LeaseAttrs, ttl time.Duration, asof uint64) (time.Time, error)
	deleteSubnet(ctx context.Context, network string, sn ip.IP4Net) error
	watchSubnets(ctx context.Context, network string, since uint64) (Event, uint64, error)
	getNetworks(ctx context.Context) ([]string, uint64, error)
	watchNetworks(ctx context.Context, since uint64) (Event, uint64, error)
}

type EtcdConfig struct {
	Endpoints []string
	Keyfile   string
	Certfile  string
	CAFile    string
	Prefix    string
}

type etcdSubnetRegistry struct {
	mux          sync.Mutex
	cli          etcd.KeysAPI
	etcdCfg      *EtcdConfig
	networkRegex *regexp.Regexp
}

func newEtcdClient(c *EtcdConfig) (etcd.KeysAPI, error) {
	tlsInfo := transport.TLSInfo{
		CertFile: c.Certfile,
		KeyFile:  c.Keyfile,
		CAFile:   c.CAFile,
	}

	t, err := transport.NewTransport(tlsInfo)
	if err != nil {
		return nil, err
	}

	cli, err := etcd.New(etcd.Config{
		Endpoints: c.Endpoints,
		Transport: t,
	})
	if err != nil {
		return nil, err
	}

	return etcd.NewKeysAPI(cli), nil
}

func newEtcdSubnetRegistry(config *EtcdConfig) (Registry, error) {
	r := &etcdSubnetRegistry{
		etcdCfg:      config,
		networkRegex: regexp.MustCompile(config.Prefix + `/([^/]*)(/|/config)?$`),
	}

	var err error
	r.cli, err = newEtcdClient(config)
	if err != nil {
		return nil, err
	}

	return r, nil
}

func (esr *etcdSubnetRegistry) getNetworkConfig(ctx context.Context, network string) (string, error) {
	key := path.Join(esr.etcdCfg.Prefix, network, "config")
	resp, err := esr.client().Get(ctx, key, nil)
	if err != nil {
		return "", err
	}
	return resp.Node.Value, nil
}

// getSubnets queries etcd to get a list of currently allocated leases for a given network.
// It returns the leases along with the "as-of" etcd-index that can be used as the starting
// point for etcd watch.
func (esr *etcdSubnetRegistry) getSubnets(ctx context.Context, network string) ([]Lease, uint64, error) {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets")
	resp, err := esr.client().Get(ctx, key, &etcd.GetOptions{Recursive: true})
	if err != nil {
		if etcdErr, ok := err.(etcd.Error); ok && etcdErr.Code == etcd.ErrorCodeKeyNotFound {
			// key not found: treat it as empty set
			return []Lease{}, etcdErr.Index, nil
		}
		return nil, 0, err
	}

	leases := []Lease{}
	for _, node := range resp.Node.Nodes {
		if sn := parseSubnetKey(node.Key); sn != nil {
			attrs := &LeaseAttrs{}
			if err = json.Unmarshal([]byte(node.Value), attrs); err == nil {
				exp := time.Time{}
				if node.Expiration != nil {
					exp = *node.Expiration
				}

				lease := Lease{
					Subnet:     *sn,
					Attrs:      *attrs,
					Expiration: exp,
				}
				leases = append(leases, lease)
			}
		}
	}

	return leases, resp.Index, nil
}

func (esr *etcdSubnetRegistry) createSubnet(ctx context.Context, network string, sn ip.IP4Net, attrs *LeaseAttrs, ttl time.Duration) (time.Time, error) {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets", sn.StringSep(".", "-"))
	value, err := json.Marshal(attrs)
	if err != nil {
		return time.Time{}, err
	}

	opts := &etcd.SetOptions{
		PrevExist: etcd.PrevNoExist,
		TTL:       ttl,
	}

	resp, err := esr.client().Set(ctx, key, string(value), opts)
	if err != nil {
		return time.Time{}, err
	}

	ensureExpiration(resp, ttl)
	return *resp.Node.Expiration, nil
}

func (esr *etcdSubnetRegistry) updateSubnet(ctx context.Context, network string, sn ip.IP4Net, attrs *LeaseAttrs, ttl time.Duration, asof uint64) (time.Time, error) {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets", sn.StringSep(".", "-"))
	value, err := json.Marshal(attrs)
	if err != nil {
		return time.Time{}, err
	}

	resp, err := esr.client().Set(ctx, key, string(value), &etcd.SetOptions{
		PrevIndex: asof,
		TTL:       ttl,
	})
	if err != nil {
		return time.Time{}, err
	}

	ensureExpiration(resp, ttl)
	return *resp.Node.Expiration, nil
}

func (esr *etcdSubnetRegistry) deleteSubnet(ctx context.Context, network string, sn ip.IP4Net) error {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets", sn.StringSep(".", "-"))
	_, err := esr.client().Delete(ctx, key, nil)
	return err
}

func (esr *etcdSubnetRegistry) watchSubnets(ctx context.Context, network string, since uint64) (Event, uint64, error) {
	key := path.Join(esr.etcdCfg.Prefix, network, "subnets")
	opts := &etcd.WatcherOptions{
		AfterIndex: since,
		Recursive:  true,
	}
	e, err := esr.client().Watcher(key, opts).Next(ctx)
	if err != nil {
		return Event{}, 0, err
	}

	evt, err := parseSubnetWatchResponse(e)
	return evt, e.Node.ModifiedIndex, err
}

// getNetworks queries etcd to get a list of network names.  It returns the
// networks along with the 'as-of' etcd-index that can be used as the starting
// point for etcd watch.
func (esr *etcdSubnetRegistry) getNetworks(ctx context.Context) ([]string, uint64, error) {
	resp, err := esr.client().Get(ctx, esr.etcdCfg.Prefix, &etcd.GetOptions{Recursive: true})

	networks := []string{}

	if err == nil {
		for _, node := range resp.Node.Nodes {
			// Look for '/config' on the child nodes
			for _, child := range node.Nodes {
				netname, isConfig := esr.parseNetworkKey(child.Key)
				if isConfig {
					networks = append(networks, netname)
				}
			}
		}

		return networks, resp.Index, nil
	}

	if etcdErr, ok := err.(etcd.Error); ok && etcdErr.Code == etcd.ErrorCodeKeyNotFound {
		// key not found: treat it as empty set
		return networks, etcdErr.Index, nil
	}

	return nil, 0, err
}

func (esr *etcdSubnetRegistry) watchNetworks(ctx context.Context, since uint64) (Event, uint64, error) {
	key := esr.etcdCfg.Prefix
	opts := &etcd.WatcherOptions{
		AfterIndex: since,
		Recursive:  true,
	}
	e, err := esr.client().Watcher(key, opts).Next(ctx)
	if err != nil {
		return Event{}, 0, err
	}

	return esr.parseNetworkWatchResponse(e)
}

func (esr *etcdSubnetRegistry) client() etcd.KeysAPI {
	esr.mux.Lock()
	defer esr.mux.Unlock()
	return esr.cli
}

func (esr *etcdSubnetRegistry) resetClient() {
	esr.mux.Lock()
	defer esr.mux.Unlock()

	var err error
	esr.cli, err = newEtcdClient(esr.etcdCfg)
	if err != nil {
		panic(fmt.Errorf("resetClient: error recreating etcd client: %v", err))
	}
}

func ensureExpiration(resp *etcd.Response, ttl time.Duration) {
	if resp.Node.Expiration == nil {
		// should not be but calc it ourselves in this case
		log.Info("Expiration field missing on etcd response, calculating locally")
		exp := clock.Now().Add(time.Duration(ttl) * time.Second)
		resp.Node.Expiration = &exp
	}
}

func parseSubnetWatchResponse(resp *etcd.Response) (Event, error) {
	sn := parseSubnetKey(resp.Node.Key)
	if sn == nil {
		return Event{}, fmt.Errorf("%v %q: not a subnet, skipping", resp.Action, resp.Node.Key)
	}

	switch resp.Action {
	case "delete", "expire":
		return Event{
			EventRemoved,
			Lease{Subnet: *sn},
			"",
		}, nil

	default:
		attrs := &LeaseAttrs{}
		err := json.Unmarshal([]byte(resp.Node.Value), attrs)
		if err != nil {
			return Event{}, err
		}

		exp := time.Time{}
		if resp.Node.Expiration != nil {
			exp = *resp.Node.Expiration
		}

		evt := Event{
			EventAdded,
			Lease{
				Subnet:     *sn,
				Attrs:      *attrs,
				Expiration: exp,
			},
			"",
		}
		return evt, nil
	}
}

func (esr *etcdSubnetRegistry) parseNetworkWatchResponse(resp *etcd.Response) (Event, uint64, error) {
	index := resp.Node.ModifiedIndex
	netname, isConfig := esr.parseNetworkKey(resp.Node.Key)
	if netname == "" {
		return Event{}, index, ErrTryAgain
	}

	evt := Event{}

	switch resp.Action {
	case "delete":
		evt = Event{
			EventRemoved,
			Lease{},
			netname,
		}

	default:
		if !isConfig {
			// Ignore non .../<netname>/config keys; tell caller to try again
			return Event{}, index, ErrTryAgain
		}

		_, err := ParseConfig(resp.Node.Value)
		if err != nil {
			return Event{}, index, err
		}

		evt = Event{
			EventAdded,
			Lease{},
			netname,
		}
	}

	return evt, index, nil
}

// Returns network name from config key (eg, /coreos.com/network/foobar/config),
// if the 'config' key isn't present we don't consider the network valid
func (esr *etcdSubnetRegistry) parseNetworkKey(s string) (string, bool) {
	if parts := esr.networkRegex.FindStringSubmatch(s); len(parts) == 3 {
		return parts[1], parts[2] != ""
	}

	return "", false
}

func parseSubnetKey(s string) *ip.IP4Net {
	if parts := subnetRegex.FindStringSubmatch(s); len(parts) == 3 {
		snIp := net.ParseIP(parts[1]).To4()
		prefixLen, err := strconv.ParseUint(parts[2], 10, 5)
		if snIp != nil && err == nil {
			return &ip.IP4Net{IP: ip.FromIP(snIp), PrefixLen: uint(prefixLen)}
		}
	}

	return nil
}