// Copyright 2016 CoreOS, Inc.
//
// 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 recipe

import (
	"sync"

	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
	"github.com/coreos/etcd/clientv3"
	"github.com/coreos/etcd/lease"
)

// only keep one ephemeral lease per client
var clientLeases clientLeaseMgr = clientLeaseMgr{leases: make(map[*clientv3.Client]*leaseKeepAlive)}

type clientLeaseMgr struct {
	leases map[*clientv3.Client]*leaseKeepAlive
	mu     sync.Mutex
}

type leaseKeepAlive struct {
	id     lease.LeaseID
	cancel context.CancelFunc
	donec  <-chan struct{}
}

func SessionLease(client *clientv3.Client) (lease.LeaseID, error) {
	return clientLeases.sessionLease(client, 120)
}

func SessionLeaseTTL(client *clientv3.Client, ttl int64) (lease.LeaseID, error) {
	return clientLeases.sessionLease(client, ttl)
}

// StopSessionLease ends the refresh for the session lease. This is useful
// in case the state of the client connection is indeterminate (revoke
// would fail) or if transferring lease ownership.
func StopSessionLease(client *clientv3.Client) {
	clientLeases.mu.Lock()
	lka := clientLeases.leases[client]
	clientLeases.mu.Unlock()
	if lka != nil {
		lka.cancel()
		<-lka.donec
	}
}

// RevokeSessionLease revokes the session lease.
func RevokeSessionLease(client *clientv3.Client) (err error) {
	clientLeases.mu.Lock()
	lka := clientLeases.leases[client]
	clientLeases.mu.Unlock()
	StopSessionLease(client)
	if lka != nil {
		_, err = clientv3.NewLease(client).Revoke(context.TODO(), lka.id)
	}
	return err
}

func (clm *clientLeaseMgr) sessionLease(client *clientv3.Client, ttl int64) (lease.LeaseID, error) {
	clm.mu.Lock()
	defer clm.mu.Unlock()
	if lka, ok := clm.leases[client]; ok {
		return lka.id, nil
	}

	lc := clientv3.NewLease(client)
	resp, err := lc.Create(context.TODO(), ttl)
	if err != nil {
		return lease.NoLease, err
	}
	id := lease.LeaseID(resp.ID)

	ctx, cancel := context.WithCancel(context.Background())
	keepAlive, err := lc.KeepAlive(ctx, id)
	if err != nil || keepAlive == nil {
		return lease.NoLease, err
	}

	donec := make(chan struct{})
	lka := &leaseKeepAlive{
		id:     id,
		cancel: cancel,
		donec:  donec}
	clm.leases[client] = lka

	// keep the lease alive until client error or cancelled context
	go func() {
		defer func() {
			clm.mu.Lock()
			delete(clm.leases, client)
			clm.mu.Unlock()
			lc.Close()
			close(donec)
		}()
		for range keepAlive {
			// eat messages until keep alive channel closes
		}
	}()

	return id, nil
}