// Copyright 2017 The etcd 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 v3election

import (
	"context"
	"errors"

	"github.com/coreos/etcd/clientv3"
	"github.com/coreos/etcd/clientv3/concurrency"
	epb "github.com/coreos/etcd/etcdserver/api/v3election/v3electionpb"
)

// ErrMissingLeaderKey is returned when election API request
// is missing the "leader" field.
var ErrMissingLeaderKey = errors.New(`"leader" field must be provided`)

type electionServer struct {
	c *clientv3.Client
}

func NewElectionServer(c *clientv3.Client) epb.ElectionServer {
	return &electionServer{c}
}

func (es *electionServer) Campaign(ctx context.Context, req *epb.CampaignRequest) (*epb.CampaignResponse, error) {
	s, err := es.session(ctx, req.Lease)
	if err != nil {
		return nil, err
	}
	e := concurrency.NewElection(s, string(req.Name))
	if err = e.Campaign(ctx, string(req.Value)); err != nil {
		return nil, err
	}
	return &epb.CampaignResponse{
		Header: e.Header(),
		Leader: &epb.LeaderKey{
			Name:  req.Name,
			Key:   []byte(e.Key()),
			Rev:   e.Rev(),
			Lease: int64(s.Lease()),
		},
	}, nil
}

func (es *electionServer) Proclaim(ctx context.Context, req *epb.ProclaimRequest) (*epb.ProclaimResponse, error) {
	if req.Leader == nil {
		return nil, ErrMissingLeaderKey
	}
	s, err := es.session(ctx, req.Leader.Lease)
	if err != nil {
		return nil, err
	}
	e := concurrency.ResumeElection(s, string(req.Leader.Name), string(req.Leader.Key), req.Leader.Rev)
	if err := e.Proclaim(ctx, string(req.Value)); err != nil {
		return nil, err
	}
	return &epb.ProclaimResponse{Header: e.Header()}, nil
}

func (es *electionServer) Observe(req *epb.LeaderRequest, stream epb.Election_ObserveServer) error {
	s, err := es.session(stream.Context(), -1)
	if err != nil {
		return err
	}
	e := concurrency.NewElection(s, string(req.Name))
	ch := e.Observe(stream.Context())
	for stream.Context().Err() == nil {
		select {
		case <-stream.Context().Done():
		case resp, ok := <-ch:
			if !ok {
				return nil
			}
			lresp := &epb.LeaderResponse{Header: resp.Header, Kv: resp.Kvs[0]}
			if err := stream.Send(lresp); err != nil {
				return err
			}
		}
	}
	return stream.Context().Err()
}

func (es *electionServer) Leader(ctx context.Context, req *epb.LeaderRequest) (*epb.LeaderResponse, error) {
	s, err := es.session(ctx, -1)
	if err != nil {
		return nil, err
	}
	l, lerr := concurrency.NewElection(s, string(req.Name)).Leader(ctx)
	if lerr != nil {
		return nil, lerr
	}
	return &epb.LeaderResponse{Header: l.Header, Kv: l.Kvs[0]}, nil
}

func (es *electionServer) Resign(ctx context.Context, req *epb.ResignRequest) (*epb.ResignResponse, error) {
	if req.Leader == nil {
		return nil, ErrMissingLeaderKey
	}
	s, err := es.session(ctx, req.Leader.Lease)
	if err != nil {
		return nil, err
	}
	e := concurrency.ResumeElection(s, string(req.Leader.Name), string(req.Leader.Key), req.Leader.Rev)
	if err := e.Resign(ctx); err != nil {
		return nil, err
	}
	return &epb.ResignResponse{Header: e.Header()}, nil
}

func (es *electionServer) session(ctx context.Context, lease int64) (*concurrency.Session, error) {
	s, err := concurrency.NewSession(
		es.c,
		concurrency.WithLease(clientv3.LeaseID(lease)),
		concurrency.WithContext(ctx),
	)
	if err != nil {
		return nil, err
	}
	s.Orphan()
	return s, nil
}