package cluster

import (
	"crypto/tls"
	"encoding/binary"
	"fmt"
	"os"
	"path/filepath"
	"sync"
	"time"

	"github.com/hashicorp/raft"
	raftboltdb "github.com/hashicorp/raft-boltdb"
	"github.com/samber/lo"
	"gitlink.org.cn/cloudream/common/pkgs/async"
	"gitlink.org.cn/cloudream/common/pkgs/logger"
	"gitlink.org.cn/cloudream/jcs-pub/common/ecode"
	"gitlink.org.cn/cloudream/jcs-pub/common/pkgs/rpc"
	clirpc "gitlink.org.cn/cloudream/jcs-pub/common/pkgs/rpc/client"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
)

type Cluster struct {
	cfg       Config
	poolCfg   clirpc.PoolConfig
	masterCli MasterClient
	doneCh    chan any
	raft      *raft.Raft
	fsm       *raftFSM
	transport *Transport
}

func New(cfg Config) *Cluster {
	return &Cluster{
		cfg: cfg,
		masterCli: MasterClient{
			Client: clirpc.NewFusedClient(rpc.Failed(ecode.OperationFailed, "master unknown")),
		},
		doneCh: make(chan any, 1),
	}
}

func (c *Cluster) Start(fsms []FSM) (*ClusterEventChan, error) {
	log := logger.WithField("Mod", "Cluster")

	ch := async.NewUnboundChannel[ClusterEvent]()
	if !c.cfg.Enabled {
		log.Infof("cluster disabled")
		return ch, nil
	}

	c.fsm = NewFSM(fsms)

	poolCfgJSON := clirpc.PoolConfigJSON{
		RootCA:     c.cfg.RootCA,
		ClientCert: c.cfg.ClientCert,
		ClientKey:  c.cfg.ClientKey,
	}

	poolCfg, err := poolCfgJSON.Build()
	if err != nil {
		return nil, fmt.Errorf("build pool config: %w", err)
	}
	c.poolCfg = *poolCfg

	raftCfg := raft.DefaultConfig()
	raftCfg.LocalID = raft.ServerID(c.cfg.Announce)

	err = os.MkdirAll(c.cfg.StoreBase, 0755)
	if err != nil {
		return nil, fmt.Errorf("create store base dir: %w", err)
	}

	logDB, err := raftboltdb.NewBoltStore(filepath.Join(c.cfg.StoreBase, "log.db"))
	if err != nil {
		return nil, fmt.Errorf("create raft log store: %w", err)
	}

	stableDB, err := raftboltdb.NewBoltStore(filepath.Join(c.cfg.StoreBase, "stable.db"))
	if err != nil {
		return nil, fmt.Errorf("create raft stable store: %w", err)
	}

	snapshotStore, err := raft.NewFileSnapshotStore(c.cfg.StoreBase, 1, os.Stdout)
	if err != nil {
		return nil, fmt.Errorf("create raft snapshot store: %w", err)
	}

	c.transport = NewTransport(c.cfg.Announce, *poolCfg)

	rft, err := raft.NewRaft(raftCfg, c.fsm, logDB, stableDB, snapshotStore, c.transport)
	if err != nil {
		return nil, fmt.Errorf("create raft: %w", err)
	}

	hasState, err := raft.HasExistingState(logDB, stableDB, snapshotStore)
	if err != nil {
		return nil, fmt.Errorf("check has existing state: %w", err)
	}

	if !hasState {
		bootCfg := raft.Configuration{}

		if !lo.Contains(c.cfg.Peers, c.cfg.Announce) {
			bootCfg.Servers = append(bootCfg.Servers, raft.Server{
				ID:      raft.ServerID(c.cfg.Announce),
				Address: raft.ServerAddress(c.cfg.Announce),
			})
		}
		for _, peer := range c.cfg.Peers {
			bootCfg.Servers = append(bootCfg.Servers, raft.Server{
				ID:      raft.ServerID(peer),
				Address: raft.ServerAddress(peer),
			})
		}

		bootFut := rft.BootstrapCluster(bootCfg)
		if err := bootFut.Error(); err != nil {
			return nil, fmt.Errorf("bootstrap cluster: %w", err)
		}

		log.Infof("bootstrap new cluster")
	} else {
		log.Infof("start existing cluster")
	}

	ch.Send(&BootstrapEvent{})
	c.raft = rft

	eventCh := make(chan raft.Observation, 1)

	obs := raft.NewObserver(eventCh, true, nil)
	rft.RegisterObserver(obs)

	go func() {
	loop:
		for {
			select {
			case <-c.doneCh:
				break loop

			case e := <-eventCh:
				state, ok := e.Data.(raft.RaftState)
				if !ok {
					continue
				}

				switch state {
				case raft.Leader:
					log.Info("become leader")

					ch.Send(&LeaderEvent{
						CurrentIsMaster: true,
						Address:         c.cfg.Announce,
					})

				case raft.Follower:
					addr, id := rft.LeaderWithID()

					log.Infof("become follower, master is: %v, %v", id, addr)

					ch.Send(&LeaderEvent{
						CurrentIsMaster: false,
						Address:         string(addr),
					})

				case raft.Candidate:
					log.Info("become candidate")
				}

			}
		}

		c.raft.DeregisterObserver(obs)
	}()

	return ch, nil
}

func (c *Cluster) Stop() {
	c.raft.Shutdown().Error()

	select {
	case c.doneCh <- nil:
	default:
	}
}

func (c *Cluster) ID() string {
	return c.cfg.Announce
}

func (c *Cluster) IsMaster() bool {
	addr, _ := c.raft.LeaderWithID()
	return string(addr) == c.cfg.Announce
}

func (c *Cluster) Enabled() bool {
	return c.cfg.Enabled
}

func (c *Cluster) Name() string {
	return c.cfg.NodeName
}

// 由于主节点可能会变化，因此不要缓存MasterClient，每次都重新获取
func (c *Cluster) MasterClient() *MasterClient {
	addr, _ := c.raft.LeaderWithID()

	c.masterCli.lock.Lock()
	defer c.masterCli.lock.Unlock()

	addr2 := string(addr)
	if addr2 == "" {
		if c.masterCli.con != nil {
			c.masterCli.con.Close()
		}

		c.masterCli.Client = clirpc.NewFusedClient(rpc.Failed(ecode.ClusterNoMaster, "no master"))
		return &c.masterCli
	}

	if c.masterCli.addr != addr2 {
		if c.masterCli.con != nil {
			c.masterCli.con.Close()
		}

		gcon, err := grpc.NewClient(addr2, grpc.WithTransportCredentials(credentials.NewTLS(&tls.Config{
			RootCAs:      c.poolCfg.Conn.RootCA,
			Certificates: []tls.Certificate{*c.poolCfg.Conn.ClientCert},
			ServerName:   rpc.InternalAPISNIV1,
			NextProtos:   []string{"h2"},
		})))
		if err != nil {
			c.masterCli.Client = clirpc.NewFusedClient(rpc.Failed(ecode.OperationFailed, "%v", err))
			c.masterCli.addr = ""
		} else {
			c.masterCli.con = gcon
			c.masterCli.Client = clirpc.NewClient(gcon)
			c.masterCli.addr = addr2
		}
	}

	return &c.masterCli
}

func (c *Cluster) RaftTransport() *Transport {
	return c.transport
}

// 只有Leader才能调用
func (c *Cluster) Apply(fsmID string, data []byte, timeout time.Duration) ([]byte, error) {
	fsmIDBytes := []byte(fsmID)

	logBytes := make([]byte, 4+len(fsmIDBytes)+len(data))

	// 前4个字节表示ID的长度，后面跟着ID和数据
	binary.LittleEndian.PutUint32(logBytes[:4], uint32(len(fsmIDBytes)))
	copy(logBytes[4:], fsmIDBytes)
	copy(logBytes[4+len(fsmIDBytes):], data)

	fut := c.raft.Apply(logBytes, timeout)
	err := fut.Error()
	if err != nil {
		return nil, err
	}

	applyRet := fut.Response().(applyResult)
	return applyRet.Result, applyRet.Error
}

type ClusterEvent interface {
	IsClusterEvent() bool
}

type ClusterEventChan = async.UnboundChannel[ClusterEvent]

type ExitEvent struct {
	Err error
}

func (e *ExitEvent) IsClusterEvent() bool {
	return true
}

type BootstrapEvent struct{}

func (e *BootstrapEvent) IsClusterEvent() bool {
	return true
}

type LeaderEvent struct {
	CurrentIsMaster bool
	Address         string
}

func (e *LeaderEvent) IsClusterEvent() bool {
	return true
}

type MasterClient struct {
	*clirpc.Client
	con  *grpc.ClientConn
	addr string
	lock sync.Mutex
}

func (c *MasterClient) Release() {

}