// Copyright 2015 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.

/*
This file contains tests which verify that the scenarios described
in the raft paper (https://raft.github.io/raft.pdf) are handled by the
raft implementation correctly. Each test focuses on several sentences
written in the paper.

Each test is composed of three parts: init, test and check.
Init part uses simple and understandable way to simulate the init state.
Test part uses Step function to generate the scenario. Check part checks
outgoing messages and state.
*/
package raft

import (
	"fmt"
	"reflect"
	"sort"
	"testing"

	pb "github.com/pingcap-incubator/tinykv/proto/pkg/eraftpb"
)

func TestFollowerUpdateTermFromMessage2AA(t *testing.T) {
	testUpdateTermFromMessage(t, StateFollower)
}
func TestCandidateUpdateTermFromMessage2AA(t *testing.T) {
	testUpdateTermFromMessage(t, StateCandidate)
}
func TestLeaderUpdateTermFromMessage2AA(t *testing.T) {
	testUpdateTermFromMessage(t, StateLeader)
}

// testUpdateTermFromMessage tests that if one server’s current term is
// smaller than the other’s, then it updates its current term to the larger
// value. If a candidate or leader discovers that its term is out of date,
// it immediately reverts to follower state.
// Reference: section 5.1
func testUpdateTermFromMessage(t *testing.T, state StateType) {
	r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
	switch state {
	case StateFollower:
		r.becomeFollower(1, 2)
	case StateCandidate:
		r.becomeCandidate()
	case StateLeader:
		r.becomeCandidate()
		r.becomeLeader()
	}

	r.Step(pb.Message{MsgType: pb.MessageType_MsgAppend, Term: 2})

	if r.Term != 2 {
		t.Errorf("term = %d, want %d", r.Term, 2)
	}
	if r.State != StateFollower {
		t.Errorf("state = %v, want %v", r.State, StateFollower)
	}
}

// TestStartAsFollower tests that when servers start up, they begin as followers.
// Reference: section 5.2
func TestStartAsFollower2AA(t *testing.T) {
	r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
	if r.State != StateFollower {
		t.Errorf("state = %s, want %s", r.State, StateFollower)
	}
}

// TestLeaderBcastBeat tests that if the leader receives a heartbeat tick,
// it will send a MessageType_MsgHeartbeat with m.Index = 0, m.LogTerm=0 and empty entries
// as heartbeat to all followers.
// Reference: section 5.2
func TestLeaderBcastBeat2AA(t *testing.T) {
	// heartbeat interval
	hi := 1
	r := newTestRaft(1, []uint64{1, 2, 3}, 10, hi, NewMemoryStorage())
	r.becomeCandidate()
	r.becomeLeader()

	r.Step(pb.Message{MsgType: pb.MessageType_MsgPropose, Entries: []*pb.Entry{{}}})
	r.readMessages() // clear message

	for i := 0; i < hi; i++ {
		r.tick()
	}

	msgs := r.readMessages()
	sort.Sort(messageSlice(msgs))
	wmsgs := []pb.Message{
		{From: 1, To: 2, Term: 1, MsgType: pb.MessageType_MsgHeartbeat},
		{From: 1, To: 3, Term: 1, MsgType: pb.MessageType_MsgHeartbeat},
	}
	if !reflect.DeepEqual(msgs, wmsgs) {
		t.Errorf("msgs = %v, want %v", msgs, wmsgs)
	}
}

func TestFollowerStartElection2AA(t *testing.T) {
	testNonleaderStartElection(t, StateFollower)
}
func TestCandidateStartNewElection2AA(t *testing.T) {
	testNonleaderStartElection(t, StateCandidate)
}

// testNonleaderStartElection tests that if a follower receives no communication
// over election timeout, it begins an election to choose a new leader. It
// increments its current term and transitions to candidate state. It then
// votes for itself and issues RequestVote RPCs in parallel to each of the
// other servers in the cluster.
// Reference: section 5.2
// Also if a candidate fails to obtain a majority, it will time out and
// start a new election by incrementing its term and initiating another
// round of RequestVote RPCs.
// Reference: section 5.2
func testNonleaderStartElection(t *testing.T, state StateType) {
	// election timeout
	et := 10
	r := newTestRaft(1, []uint64{1, 2, 3}, et, 1, NewMemoryStorage())
	switch state {
	case StateFollower:
		r.becomeFollower(1, 2)
	case StateCandidate:
		r.becomeCandidate()
	}

	for i := 1; i < 2*et; i++ {
		r.tick()
	}

	if r.Term != 2 {
		t.Errorf("term = %d, want 2", r.Term)
	}
	if r.State != StateCandidate {
		t.Errorf("state = %s, want %s", r.State, StateCandidate)
	}
	if !r.votes[r.id] {
		t.Errorf("vote for self = false, want true")
	}
	msgs := r.readMessages()
	sort.Sort(messageSlice(msgs))
	wmsgs := []pb.Message{
		{From: 1, To: 2, Term: 2, MsgType: pb.MessageType_MsgRequestVote},
		{From: 1, To: 3, Term: 2, MsgType: pb.MessageType_MsgRequestVote},
	}
	if !reflect.DeepEqual(msgs, wmsgs) {
		t.Errorf("msgs = %v, want %v", msgs, wmsgs)
	}
}

// TestLeaderElectionInOneRoundRPC tests all cases that may happen in
// leader election during one round of RequestVote RPC:
// a) it wins the election
// b) it loses the election
// c) it is unclear about the result
// Reference: section 5.2
func TestLeaderElectionInOneRoundRPC2AA(t *testing.T) {
	tests := []struct {
		size  int
		votes map[uint64]bool
		state StateType
	}{
		// win the election when receiving votes from a majority of the servers
		{1, map[uint64]bool{}, StateLeader},
		{3, map[uint64]bool{2: true, 3: true}, StateLeader},
		{3, map[uint64]bool{2: true}, StateLeader},
		{5, map[uint64]bool{2: true, 3: true, 4: true, 5: true}, StateLeader},
		{5, map[uint64]bool{2: true, 3: true, 4: true}, StateLeader},
		{5, map[uint64]bool{2: true, 3: true}, StateLeader},

		// stay in candidate if it does not obtain the majority
		{3, map[uint64]bool{}, StateCandidate},
		{5, map[uint64]bool{2: true}, StateCandidate},
		{5, map[uint64]bool{2: false, 3: false}, StateCandidate},
		{5, map[uint64]bool{}, StateCandidate},
	}
	for i, tt := range tests {
		r := newTestRaft(1, idsBySize(tt.size), 10, 1, NewMemoryStorage())

		r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgHup})
		for id, vote := range tt.votes {
			r.Step(pb.Message{From: id, To: 1, Term: r.Term, MsgType: pb.MessageType_MsgRequestVoteResponse, Reject: !vote})
		}

		if r.State != tt.state {
			t.Errorf("#%d: state = %s, want %s", i, r.State, tt.state)
		}
		if g := r.Term; g != 1 {
			t.Errorf("#%d: term = %d, want %d", i, g, 1)
		}
	}
}

// TestFollowerVote tests that each follower will vote for at most one
// candidate in a given term, on a first-come-first-served basis.
// Reference: section 5.2
func TestFollowerVote2AA(t *testing.T) {
	tests := []struct {
		vote    uint64
		nvote   uint64
		wreject bool
	}{
		{None, 1, false},
		{None, 2, false},
		{1, 1, false},
		{2, 2, false},
		{1, 2, true},
		{2, 1, true},
	}
	for i, tt := range tests {
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
		r.Term = 1
		r.Vote = tt.vote

		r.Step(pb.Message{From: tt.nvote, To: 1, Term: 1, MsgType: pb.MessageType_MsgRequestVote})

		msgs := r.readMessages()
		wmsgs := []pb.Message{
			{From: 1, To: tt.nvote, Term: 1, MsgType: pb.MessageType_MsgRequestVoteResponse, Reject: tt.wreject},
		}
		if !reflect.DeepEqual(msgs, wmsgs) {
			t.Errorf("#%d: msgs = %v, want %v", i, msgs, wmsgs)
		}
	}
}

// TestCandidateFallback tests that while waiting for votes,
// if a candidate receives an AppendEntries RPC from another server claiming
// to be leader whose term is at least as large as the candidate's current term,
// it recognizes the leader as legitimate and returns to follower state.
// Reference: section 5.2
func TestCandidateFallback2AA(t *testing.T) {
	tests := []pb.Message{
		{From: 2, To: 1, Term: 1, MsgType: pb.MessageType_MsgAppend},
		{From: 2, To: 1, Term: 2, MsgType: pb.MessageType_MsgAppend},
	}
	for i, tt := range tests {
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
		r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgHup})
		if r.State != StateCandidate {
			t.Fatalf("unexpected state = %s, want %s", r.State, StateCandidate)
		}

		r.Step(tt)

		if g := r.State; g != StateFollower {
			t.Errorf("#%d: state = %s, want %s", i, g, StateFollower)
		}
		if g := r.Term; g != tt.Term {
			t.Errorf("#%d: term = %d, want %d", i, g, tt.Term)
		}
	}
}

func TestFollowerElectionTimeoutRandomized2AA(t *testing.T) {
	testNonleaderElectionTimeoutRandomized(t, StateFollower)
}
func TestCandidateElectionTimeoutRandomized2AA(t *testing.T) {
	testNonleaderElectionTimeoutRandomized(t, StateCandidate)
}

// testNonleaderElectionTimeoutRandomized tests that election timeout for
// follower or candidate is randomized.
// Reference: section 5.2
func testNonleaderElectionTimeoutRandomized(t *testing.T, state StateType) {
	et := 10
	r := newTestRaft(1, []uint64{1, 2, 3}, et, 1, NewMemoryStorage())
	timeouts := make(map[int]bool)
	for round := 0; round < 50*et; round++ {
		switch state {
		case StateFollower:
			r.becomeFollower(r.Term+1, 2)
		case StateCandidate:
			r.becomeCandidate()
		}

		time := 0
		for len(r.readMessages()) == 0 {
			r.tick()
			time++
		}
		timeouts[time] = true
	}

	for d := et + 1; d < 2*et; d++ {
		if !timeouts[d] {
			t.Errorf("timeout in %d ticks should happen", d)
		}
	}
}

func TestFollowersElectionTimeoutNonconflict2AA(t *testing.T) {
	testNonleadersElectionTimeoutNonconflict(t, StateFollower)
}
func TestCandidatesElectionTimeoutNonconflict2AA(t *testing.T) {
	testNonleadersElectionTimeoutNonconflict(t, StateCandidate)
}

// testNonleadersElectionTimeoutNonconflict tests that in most cases only a
// single server(follower or candidate) will time out, which reduces the
// likelihood of split vote in the new election.
// Reference: section 5.2
func testNonleadersElectionTimeoutNonconflict(t *testing.T, state StateType) {
	et := 10
	size := 5
	rs := make([]*Raft, size)
	ids := idsBySize(size)
	for k := range rs {
		rs[k] = newTestRaft(ids[k], ids, et, 1, NewMemoryStorage())
	}
	conflicts := 0
	for round := 0; round < 1000; round++ {
		for _, r := range rs {
			switch state {
			case StateFollower:
				r.becomeFollower(r.Term+1, None)
			case StateCandidate:
				r.becomeCandidate()
			}
		}

		timeoutNum := 0
		for timeoutNum == 0 {
			for _, r := range rs {
				r.tick()
				if len(r.readMessages()) > 0 {
					timeoutNum++
				}
			}
		}
		// several rafts time out at the same tick
		if timeoutNum > 1 {
			conflicts++
		}
	}

	if g := float64(conflicts) / 1000; g > 0.3 {
		t.Errorf("probability of conflicts = %v, want <= 0.3", g)
	}
}

// TestLeaderStartReplication tests that when receiving client proposals,
// the leader appends the proposal to its log as a new entry, then issues
// AppendEntries RPCs in parallel to each of the other servers to replicate
// the entry. Also, when sending an AppendEntries RPC, the leader includes
// the index and term of the entry in its log that immediately precedes
// the new entries.
// Also, it writes the new entry into stable storage.
// Reference: section 5.3
func TestLeaderStartReplication2AB(t *testing.T) {
	s := NewMemoryStorage()
	r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, s)
	r.becomeCandidate()
	r.becomeLeader()
	commitNoopEntry(r, s)
	li := r.RaftLog.LastIndex()

	ents := []*pb.Entry{{Data: []byte("some data")}}
	r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgPropose, Entries: ents})

	if g := r.RaftLog.LastIndex(); g != li+1 {
		t.Errorf("lastIndex = %d, want %d", g, li+1)
	}
	if g := r.RaftLog.committed; g != li {
		t.Errorf("committed = %d, want %d", g, li)
	}
	msgs := r.readMessages()
	sort.Sort(messageSlice(msgs))
	ent := pb.Entry{Index: li + 1, Term: 1, Data: []byte("some data")}
	wents := []pb.Entry{ent}
	wmsgs := []pb.Message{
		{From: 1, To: 2, Term: 1, MsgType: pb.MessageType_MsgAppend, Index: li, LogTerm: 1, Entries: []*pb.Entry{&ent}, Commit: li},
		{From: 1, To: 3, Term: 1, MsgType: pb.MessageType_MsgAppend, Index: li, LogTerm: 1, Entries: []*pb.Entry{&ent}, Commit: li},
	}
	if !reflect.DeepEqual(msgs, wmsgs) {
		t.Errorf("msgs = %+v, want %+v", msgs, wmsgs)
	}
	if g := r.RaftLog.unstableEntries(); !reflect.DeepEqual(g, wents) {
		t.Errorf("ents = %+v, want %+v", g, wents)
	}
}

// TestLeaderCommitEntry tests that when the entry has been safely replicated,
// the leader gives out the applied entries, which can be applied to its state
// machine.
// Also, the leader keeps track of the highest index it knows to be committed,
// and it includes that index in future AppendEntries RPCs so that the other
// servers eventually find out.
// Reference: section 5.3
func TestLeaderCommitEntry2AB(t *testing.T) {
	s := NewMemoryStorage()
	r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, s)
	r.becomeCandidate()
	r.becomeLeader()
	commitNoopEntry(r, s)
	li := r.RaftLog.LastIndex()
	r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgPropose, Entries: []*pb.Entry{{Data: []byte("some data")}}})

	for _, m := range r.readMessages() {
		r.Step(acceptAndReply(m))
	}

	if g := r.RaftLog.committed; g != li+1 {
		t.Errorf("committed = %d, want %d", g, li+1)
	}
	wents := []pb.Entry{{Index: li + 1, Term: 1, Data: []byte("some data")}}
	if g := r.RaftLog.nextEnts(); !reflect.DeepEqual(g, wents) {
		t.Errorf("nextEnts = %+v, want %+v", g, wents)
	}
	msgs := r.readMessages()
	sort.Sort(messageSlice(msgs))
	for i, m := range msgs {
		if w := uint64(i + 2); m.To != w {
			t.Errorf("to = %d, want %d", m.To, w)
		}
		if m.MsgType != pb.MessageType_MsgAppend {
			t.Errorf("type = %v, want %v", m.MsgType, pb.MessageType_MsgAppend)
		}
		if m.Commit != li+1 {
			t.Errorf("commit = %d, want %d", m.Commit, li+1)
		}
	}
}

// TestLeaderAcknowledgeCommit tests that a log entry is committed once the
// leader that created the entry has replicated it on a majority of the servers.
// Reference: section 5.3
func TestLeaderAcknowledgeCommit2AB(t *testing.T) {
	tests := []struct {
		size      int
		acceptors map[uint64]bool
		wack      bool
	}{
		{1, nil, true},
		{3, nil, false},
		{3, map[uint64]bool{2: true}, true},
		{3, map[uint64]bool{2: true, 3: true}, true},
		{5, nil, false},
		{5, map[uint64]bool{2: true}, false},
		{5, map[uint64]bool{2: true, 3: true}, true},
		{5, map[uint64]bool{2: true, 3: true, 4: true}, true},
		{5, map[uint64]bool{2: true, 3: true, 4: true, 5: true}, true},
	}
	for i, tt := range tests {
		s := NewMemoryStorage()
		r := newTestRaft(1, idsBySize(tt.size), 10, 1, s)
		r.becomeCandidate()
		r.becomeLeader()
		commitNoopEntry(r, s)
		li := r.RaftLog.LastIndex()
		r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgPropose, Entries: []*pb.Entry{{Data: []byte("some data")}}})

		for _, m := range r.readMessages() {
			if tt.acceptors[m.To] {
				r.Step(acceptAndReply(m))
			}
		}

		if g := r.RaftLog.committed > li; g != tt.wack {
			t.Errorf("#%d: ack commit = %v, want %v", i, g, tt.wack)
		}
	}
}

// TestLeaderCommitPrecedingEntries tests that when leader commits a log entry,
// it also commits all preceding entries in the leader’s log, including
// entries created by previous leaders.
// Also, it applies the entry to its local state machine (in log order).
// Reference: section 5.3
func TestLeaderCommitPrecedingEntries2AB(t *testing.T) {
	tests := [][]pb.Entry{
		{},
		{{Term: 2, Index: 1}},
		{{Term: 1, Index: 1}, {Term: 2, Index: 2}},
		{{Term: 1, Index: 1}},
	}
	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.Append(tt)
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, storage)
		r.Term = 2
		r.becomeCandidate()
		r.becomeLeader()
		r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgPropose, Entries: []*pb.Entry{{Data: []byte("some data")}}})

		for _, m := range r.readMessages() {
			r.Step(acceptAndReply(m))
		}

		li := uint64(len(tt))
		wents := append(tt, pb.Entry{Term: 3, Index: li + 1}, pb.Entry{Term: 3, Index: li + 2, Data: []byte("some data")})
		if g := r.RaftLog.nextEnts(); !reflect.DeepEqual(g, wents) {
			t.Errorf("#%d: ents = %+v, want %+v", i, g, wents)
		}
	}
}

// TestFollowerCommitEntry tests that once a follower learns that a log entry
// is committed, it applies the entry to its local state machine (in log order).
// Reference: section 5.3
func TestFollowerCommitEntry2AB(t *testing.T) {
	tests := []struct {
		ents   []*pb.Entry
		commit uint64
	}{
		{
			[]*pb.Entry{
				{Term: 1, Index: 1, Data: []byte("some data")},
			},
			1,
		},
		{
			[]*pb.Entry{
				{Term: 1, Index: 1, Data: []byte("some data")},
				{Term: 1, Index: 2, Data: []byte("some data2")},
			},
			2,
		},
		{
			[]*pb.Entry{
				{Term: 1, Index: 1, Data: []byte("some data2")},
				{Term: 1, Index: 2, Data: []byte("some data")},
			},
			2,
		},
		{
			[]*pb.Entry{
				{Term: 1, Index: 1, Data: []byte("some data")},
				{Term: 1, Index: 2, Data: []byte("some data2")},
			},
			1,
		},
	}
	for i, tt := range tests {
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
		r.becomeFollower(1, 2)

		r.Step(pb.Message{From: 2, To: 1, MsgType: pb.MessageType_MsgAppend, Term: 1, Entries: tt.ents, Commit: tt.commit})

		if g := r.RaftLog.committed; g != tt.commit {
			t.Errorf("#%d: committed = %d, want %d", i, g, tt.commit)
		}
		wents := make([]pb.Entry, 0, tt.commit)
		for _, ent := range tt.ents[:int(tt.commit)] {
			wents = append(wents, *ent)
		}
		if g := r.RaftLog.nextEnts(); !reflect.DeepEqual(g, wents) {
			t.Errorf("#%d: nextEnts = %v, want %v", i, g, wents)
		}
	}
}

// TestFollowerCheckMessageType_MsgAppend tests that if the follower does not find an
// entry in its log with the same index and term as the one in AppendEntries RPC,
// then it refuses the new entries. Otherwise it replies that it accepts the
// append entries.
// Reference: section 5.3
func TestFollowerCheckMessageType_MsgAppend2AB(t *testing.T) {
	ents := []pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}}
	tests := []struct {
		term    uint64
		index   uint64
		wreject bool
	}{
		// match with committed entries
		{0, 0, false},
		{ents[0].Term, ents[0].Index, false},
		// match with uncommitted entries
		{ents[1].Term, ents[1].Index, false},

		// unmatch with existing entry
		{ents[0].Term, ents[1].Index, true},
		// unexisting entry
		{ents[1].Term + 1, ents[1].Index + 1, true},
	}
	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.Append(ents)
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, storage)
		r.RaftLog.committed = 1
		r.becomeFollower(2, 2)
		msgs := r.readMessages() // clear message

		r.Step(pb.Message{From: 2, To: 1, MsgType: pb.MessageType_MsgAppend, Term: 2, LogTerm: tt.term, Index: tt.index})

		msgs = r.readMessages()
		if len(msgs) != 1 {
			t.Errorf("#%d: len(msgs) = %+v, want %+v", i, len(msgs), 1)
		}
		if msgs[0].Term != 2 {
			t.Errorf("#%d: term = %+v, want %+v", i, msgs[0].Term, 2)
		}
		if msgs[0].Reject != tt.wreject {
			t.Errorf("#%d: reject = %+v, want %+v", i, msgs[0].Reject, tt.wreject)
		}
	}
}

// TestFollowerAppendEntries tests that when AppendEntries RPC is valid,
// the follower will delete the existing conflict entry and all that follow it,
// and append any new entries not already in the log.
// Also, it writes the new entry into stable storage.
// Reference: section 5.3
func TestFollowerAppendEntries2AB(t *testing.T) {
	tests := []struct {
		index, term uint64
		lterm       uint64
		ents        []*pb.Entry
		wents       []*pb.Entry
		wunstable   []*pb.Entry
	}{
		{
			2, 2, 3,
			[]*pb.Entry{{Term: 3, Index: 3}},
			[]*pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}, {Term: 3, Index: 3}},
			[]*pb.Entry{{Term: 3, Index: 3}},
		},
		{
			1, 1, 4,
			[]*pb.Entry{{Term: 3, Index: 2}, {Term: 4, Index: 3}},
			[]*pb.Entry{{Term: 1, Index: 1}, {Term: 3, Index: 2}, {Term: 4, Index: 3}},
			[]*pb.Entry{{Term: 3, Index: 2}, {Term: 4, Index: 3}},
		},
		{
			0, 0, 2,
			[]*pb.Entry{{Term: 1, Index: 1}},
			[]*pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}},
			[]*pb.Entry{},
		},
		{
			0, 0, 3,
			[]*pb.Entry{{Term: 3, Index: 1}},
			[]*pb.Entry{{Term: 3, Index: 1}},
			[]*pb.Entry{{Term: 3, Index: 1}},
		},
	}
	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.Append([]pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}})
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, storage)
		r.becomeFollower(2, 2)

		r.Step(pb.Message{From: 2, To: 1, MsgType: pb.MessageType_MsgAppend, Term: tt.lterm, LogTerm: tt.term, Index: tt.index, Entries: tt.ents})

		wents := make([]pb.Entry, 0, len(tt.wents))
		for _, ent := range tt.wents {
			wents = append(wents, *ent)
		}
		if g := r.RaftLog.entries; !reflect.DeepEqual(g, wents) {
			t.Errorf("#%d: ents = %+v, want %+v", i, g, wents)
		}
		var wunstable []pb.Entry
		if tt.wunstable != nil {
			wunstable = make([]pb.Entry, 0, len(tt.wunstable))
		}
		for _, ent := range tt.wunstable {
			wunstable = append(wunstable, *ent)
		}
		if g := r.RaftLog.unstableEntries(); !reflect.DeepEqual(g, wunstable) {
			t.Errorf("#%d: unstableEnts = %+v, want %+v", i, g, wunstable)
		}
	}
}

// TestLeaderSyncFollowerLog tests that the leader could bring a follower's log
// into consistency with its own.
// Reference: section 5.3, figure 7
func TestLeaderSyncFollowerLog2AB(t *testing.T) {
	ents := []pb.Entry{
		{},
		{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
		{Term: 4, Index: 4}, {Term: 4, Index: 5},
		{Term: 5, Index: 6}, {Term: 5, Index: 7},
		{Term: 6, Index: 8}, {Term: 6, Index: 9}, {Term: 6, Index: 10},
	}
	term := uint64(8)
	tests := [][]pb.Entry{
		{
			{},
			{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
			{Term: 4, Index: 4}, {Term: 4, Index: 5},
			{Term: 5, Index: 6}, {Term: 5, Index: 7},
			{Term: 6, Index: 8}, {Term: 6, Index: 9},
		},
		{
			{},
			{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
			{Term: 4, Index: 4},
		},
		{
			{},
			{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
			{Term: 4, Index: 4}, {Term: 4, Index: 5},
			{Term: 5, Index: 6}, {Term: 5, Index: 7},
			{Term: 6, Index: 8}, {Term: 6, Index: 9}, {Term: 6, Index: 10}, {Term: 6, Index: 11},
		},
		{
			{},
			{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
			{Term: 4, Index: 4}, {Term: 4, Index: 5},
			{Term: 5, Index: 6}, {Term: 5, Index: 7},
			{Term: 6, Index: 8}, {Term: 6, Index: 9}, {Term: 6, Index: 10},
			{Term: 7, Index: 11}, {Term: 7, Index: 12},
		},
		{
			{},
			{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
			{Term: 4, Index: 4}, {Term: 4, Index: 5}, {Term: 4, Index: 6}, {Term: 4, Index: 7},
		},
		{
			{},
			{Term: 1, Index: 1}, {Term: 1, Index: 2}, {Term: 1, Index: 3},
			{Term: 2, Index: 4}, {Term: 2, Index: 5}, {Term: 2, Index: 6},
			{Term: 3, Index: 7}, {Term: 3, Index: 8}, {Term: 3, Index: 9}, {Term: 3, Index: 10}, {Term: 3, Index: 11},
		},
	}
	for i, tt := range tests {
		leadStorage := NewMemoryStorage()
		leadStorage.Append(ents)
		lead := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, leadStorage)
		lead.Term = term
		lead.RaftLog.committed = lead.RaftLog.LastIndex()
		followerStorage := NewMemoryStorage()
		followerStorage.Append(tt)
		follower := newTestRaft(2, []uint64{1, 2, 3}, 10, 1, followerStorage)
		follower.Term = term - 1
		// It is necessary to have a three-node cluster.
		// The second may have more up-to-date log than the first one, so the
		// first node needs the vote from the third node to become the leader.
		n := newNetwork(lead, follower, nopStepper)
		n.send(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgHup})
		// The election occurs in the term after the one we loaded with
		// lead's term and commited index setted up above.
		n.send(pb.Message{From: 3, To: 1, MsgType: pb.MessageType_MsgRequestVoteResponse, Term: term + 1})

		n.send(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgPropose, Entries: []*pb.Entry{{}}})

		if g := diffu(ltoa(lead.RaftLog), ltoa(follower.RaftLog)); g != "" {
			t.Errorf("#%d: log diff:\n%s", i, g)
		}
	}
}

// TestVoteRequest tests that the vote request includes information about the candidate’s log
// and are sent to all of the other nodes.
// Reference: section 5.4.1
func TestVoteRequest2AB(t *testing.T) {
	tests := []struct {
		ents  []*pb.Entry
		wterm uint64
	}{
		{[]*pb.Entry{{Term: 1, Index: 1}}, 2},
		{[]*pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}}, 3},
	}
	for j, tt := range tests {
		r := newTestRaft(1, []uint64{1, 2, 3}, 10, 1, NewMemoryStorage())
		r.Step(pb.Message{
			From: 2, To: 1, MsgType: pb.MessageType_MsgAppend, Term: tt.wterm - 1, LogTerm: 0, Index: 0, Entries: tt.ents,
		})
		r.readMessages()

		for r.State != StateCandidate {
			r.tick()
		}

		msgs := r.readMessages()
		sort.Sort(messageSlice(msgs))
		if len(msgs) != 2 {
			t.Fatalf("#%d: len(msg) = %d, want %d", j, len(msgs), 2)
		}
		for i, m := range msgs {
			if m.MsgType != pb.MessageType_MsgRequestVote {
				t.Errorf("#%d: msgType = %d, want %d", i, m.MsgType, pb.MessageType_MsgRequestVote)
			}
			if m.To != uint64(i+2) {
				t.Errorf("#%d: to = %d, want %d", i, m.To, i+2)
			}
			if m.Term != tt.wterm {
				t.Errorf("#%d: term = %d, want %d", i, m.Term, tt.wterm)
			}
			windex, wlogterm := tt.ents[len(tt.ents)-1].Index, tt.ents[len(tt.ents)-1].Term
			if m.Index != windex {
				t.Errorf("#%d: index = %d, want %d", i, m.Index, windex)
			}
			if m.LogTerm != wlogterm {
				t.Errorf("#%d: logterm = %d, want %d", i, m.LogTerm, wlogterm)
			}
		}
	}
}

// TestVoter tests the voter denies its vote if its own log is more up-to-date
// than that of the candidate.
// Reference: section 5.4.1
func TestVoter2AB(t *testing.T) {
	tests := []struct {
		ents    []pb.Entry
		logterm uint64
		index   uint64

		wreject bool
	}{
		// same logterm
		{[]pb.Entry{{Term: 1, Index: 1}}, 1, 1, false},
		{[]pb.Entry{{Term: 1, Index: 1}}, 1, 2, false},
		{[]pb.Entry{{Term: 1, Index: 1}, {Term: 1, Index: 2}}, 1, 1, true},
		// candidate higher logterm
		{[]pb.Entry{{Term: 1, Index: 1}}, 2, 1, false},
		{[]pb.Entry{{Term: 1, Index: 1}}, 2, 2, false},
		{[]pb.Entry{{Term: 1, Index: 1}, {Term: 1, Index: 2}}, 2, 1, false},
		// voter higher logterm
		{[]pb.Entry{{Term: 2, Index: 1}}, 1, 1, true},
		{[]pb.Entry{{Term: 2, Index: 1}}, 1, 2, true},
		{[]pb.Entry{{Term: 2, Index: 1}, {Term: 1, Index: 2}}, 1, 1, true},
	}
	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.Append(tt.ents)
		r := newTestRaft(1, []uint64{1, 2}, 10, 1, storage)

		r.Step(pb.Message{From: 2, To: 1, MsgType: pb.MessageType_MsgRequestVote, Term: 3, LogTerm: tt.logterm, Index: tt.index})

		msgs := r.readMessages()
		if len(msgs) != 1 {
			t.Fatalf("#%d: len(msg) = %d, want %d", i, len(msgs), 1)
		}
		m := msgs[0]
		if m.MsgType != pb.MessageType_MsgRequestVoteResponse {
			t.Errorf("#%d: msgType = %d, want %d", i, m.MsgType, pb.MessageType_MsgRequestVoteResponse)
		}
		if m.Reject != tt.wreject {
			t.Errorf("#%d: reject = %t, want %t", i, m.Reject, tt.wreject)
		}
	}
}

// TestLeaderOnlyCommitsLogFromCurrentTerm tests that only log entries from the leader’s
// current term are committed by counting replicas.
// Reference: section 5.4.2
func TestLeaderOnlyCommitsLogFromCurrentTerm2AB(t *testing.T) {
	ents := []pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}}
	tests := []struct {
		index   uint64
		wcommit uint64
	}{
		// do not commit log entries in previous terms
		{1, 0},
		{2, 0},
		// commit log in current term
		{3, 3},
	}
	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.Append(ents)
		r := newTestRaft(1, []uint64{1, 2}, 10, 1, storage)
		r.Term = 2
		// become leader at term 3
		r.becomeCandidate()
		r.becomeLeader()
		r.readMessages()
		// propose a entry to current term
		r.Step(pb.Message{From: 1, To: 1, MsgType: pb.MessageType_MsgPropose, Entries: []*pb.Entry{{}}})

		r.Step(pb.Message{From: 2, To: 1, MsgType: pb.MessageType_MsgAppendResponse, Term: r.Term, Index: tt.index})
		if r.RaftLog.committed != tt.wcommit {
			t.Errorf("#%d: commit = %d, want %d", i, r.RaftLog.committed, tt.wcommit)
		}
	}
}

type messageSlice []pb.Message

func (s messageSlice) Len() int           { return len(s) }
func (s messageSlice) Less(i, j int) bool { return fmt.Sprint(s[i]) < fmt.Sprint(s[j]) }
func (s messageSlice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

func commitNoopEntry(r *Raft, s *MemoryStorage) {
	if r.State != StateLeader {
		panic("it should only be used when it is the leader")
	}
	for id := range r.Prs {
		if id == r.id {
			continue
		}

		r.sendAppend(id)
	}
	// simulate the response of MessageType_MsgAppend
	msgs := r.readMessages()
	for _, m := range msgs {
		if m.MsgType != pb.MessageType_MsgAppend || len(m.Entries) != 1 || m.Entries[0].Data != nil {
			panic("not a message to append noop entry")
		}
		r.Step(acceptAndReply(m))
	}
	// ignore further messages to refresh followers' commit index
	r.readMessages()
	s.Append(r.RaftLog.unstableEntries())
	r.RaftLog.applied = r.RaftLog.committed
	r.RaftLog.stabled = r.RaftLog.LastIndex()
}

func acceptAndReply(m pb.Message) pb.Message {
	if m.MsgType != pb.MessageType_MsgAppend {
		panic("type should be MessageType_MsgAppend")
	}
	// Note: reply message don't contain LogTerm
	return pb.Message{
		From:    m.To,
		To:      m.From,
		Term:    m.Term,
		MsgType: pb.MessageType_MsgAppendResponse,
		Index:   m.Index + uint64(len(m.Entries)),
	}
}