/*
   Copyright 2014 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 etcdserver

import (
	"encoding/json"
	"log"
	"sort"

	"github.com/coreos/etcd/pkg/pbutil"
	"github.com/coreos/etcd/pkg/types"
	"github.com/coreos/etcd/raft"
	"github.com/coreos/etcd/raft/raftpb"
	"github.com/coreos/etcd/wal"
)

func restartAsStandaloneNode(cfg *ServerConfig, index uint64, snapshot *raftpb.Snapshot) (types.ID, raft.Node, *raft.MemoryStorage, *wal.WAL) {
	w, id, cid, st, ents := readWAL(cfg.WALDir(), index)
	cfg.Cluster.SetID(cid)

	// discard the previously uncommitted entries
	for i, ent := range ents {
		if ent.Index > st.Commit {
			log.Printf("etcdserver: discarding %d uncommitted WAL entries ", len(ents)-i)
			ents = ents[:i]
			break
		}
	}

	// force append the configuration change entries
	toAppEnts := createConfigChangeEnts(getIDs(snapshot, ents), uint64(id), st.Term, st.Commit)
	ents = append(ents, toAppEnts...)

	// force commit newly appended entries
	for _, e := range toAppEnts {
		err := w.SaveEntry(&e)
		if err != nil {
			log.Fatalf("etcdserver: %v", err)
		}
	}
	if len(ents) != 0 {
		st.Commit = ents[len(ents)-1].Index
	}

	log.Printf("etcdserver: forcing restart of member %s in cluster %s at commit index %d", id, cfg.Cluster.ID(), st.Commit)
	s := raft.NewMemoryStorage()
	if snapshot != nil {
		s.ApplySnapshot(*snapshot)
	}
	s.SetHardState(st)
	s.Append(ents)
	n := raft.RestartNode(uint64(id), 10, 1, s)
	return id, n, s, w
}

// getIDs returns an ordered set of IDs included in the given snapshot and
// the entries. The given snapshot/entries can contain two kinds of
// ID-related entry:
// - ConfChangeAddNode, in which case the contained ID will be added into the set.
// - ConfChangeAddRemove, in which case the contained ID will be removed from the set.
func getIDs(snap *raftpb.Snapshot, ents []raftpb.Entry) []uint64 {
	ids := make(map[uint64]bool)
	if snap != nil {
		for _, id := range snap.Metadata.ConfState.Nodes {
			ids[id] = true
		}
	}
	for _, e := range ents {
		if e.Type != raftpb.EntryConfChange {
			continue
		}
		var cc raftpb.ConfChange
		pbutil.MustUnmarshal(&cc, e.Data)
		switch cc.Type {
		case raftpb.ConfChangeAddNode:
			ids[cc.NodeID] = true
		case raftpb.ConfChangeRemoveNode:
			delete(ids, cc.NodeID)
		default:
			log.Panicf("ConfChange Type should be either ConfChangeAddNode or ConfChangeRemoveNode!")
		}
	}
	sids := make(types.Uint64Slice, 0)
	for id := range ids {
		sids = append(sids, id)
	}
	sort.Sort(sids)
	return []uint64(sids)
}

// createConfigChangeEnts creates a series of Raft entries (i.e.
// EntryConfChange) to remove the set of given IDs from the cluster. The ID
// `self` is _not_ removed, even if present in the set.
// If `self` is not inside the given ids, it creates a Raft entry to add a
// default member with the given `self`.
func createConfigChangeEnts(ids []uint64, self uint64, term, index uint64) []raftpb.Entry {
	ents := make([]raftpb.Entry, 0)
	next := index + 1
	found := false
	for _, id := range ids {
		if id == self {
			found = true
			continue
		}
		cc := &raftpb.ConfChange{
			Type:   raftpb.ConfChangeRemoveNode,
			NodeID: id,
		}
		e := raftpb.Entry{
			Type:  raftpb.EntryConfChange,
			Data:  pbutil.MustMarshal(cc),
			Term:  term,
			Index: next,
		}
		ents = append(ents, e)
		next++
	}
	if !found {
		m := Member{
			ID:             types.ID(self),
			RaftAttributes: RaftAttributes{PeerURLs: []string{"http://localhost:7001", "http://localhost:2380"}},
		}
		ctx, err := json.Marshal(m)
		if err != nil {
			log.Panicf("marshal member should never fail: %v", err)
		}
		cc := &raftpb.ConfChange{
			Type:    raftpb.ConfChangeAddNode,
			NodeID:  self,
			Context: ctx,
		}
		e := raftpb.Entry{
			Type:  raftpb.EntryConfChange,
			Data:  pbutil.MustMarshal(cc),
			Term:  term,
			Index: next,
		}
		ents = append(ents, e)
	}
	return ents
}