package nomad

import (
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"math/rand"
	"net"
	"net/rpc"
	"strings"
	"time"

	metrics "github.com/armon/go-metrics"
	"github.com/hashicorp/consul/lib"
	memdb "github.com/hashicorp/go-memdb"
	msgpackrpc "github.com/hashicorp/net-rpc-msgpackrpc"
	"github.com/hashicorp/nomad/nomad/state"
	"github.com/hashicorp/nomad/nomad/structs"
	"github.com/hashicorp/raft"
	"github.com/hashicorp/yamux"
)

type RPCType byte

const (
	rpcNomad     RPCType = 0x01
	rpcRaft              = 0x02
	rpcMultiplex         = 0x03
	rpcTLS               = 0x04
)

const (
	// maxQueryTime is used to bound the limit of a blocking query
	maxQueryTime = 300 * time.Second

	// defaultQueryTime is the amount of time we block waiting for a change
	// if no time is specified. Previously we would wait the maxQueryTime.
	defaultQueryTime = 300 * time.Second

	// jitterFraction is a the limit to the amount of jitter we apply
	// to a user specified MaxQueryTime. We divide the specified time by
	// the fraction. So 16 == 6.25% limit of jitter. This jitter is also
	// applied to RPCHoldTimeout.
	jitterFraction = 16

	// Warn if the Raft command is larger than this.
	// If it's over 1MB something is probably being abusive.
	raftWarnSize = 1024 * 1024

	// enqueueLimit caps how long we will wait to enqueue
	// a new Raft command. Something is probably wrong if this
	// value is ever reached. However, it prevents us from blocking
	// the requesting goroutine forever.
	enqueueLimit = 30 * time.Second
)

// RPCContext provides metadata about the RPC connection.
type RPCContext struct {
	// Conn exposes the raw connection.
	Conn net.Conn

	// Session exposes the multiplexed connection session.
	Session *yamux.Session

	// TLS marks whether the RPC is over a TLS based connection
	TLS bool

	// TLSRole is the certificate role making the TLS connection.
	TLSRole string

	// TLSRegion is the region on the certificate making the TLS connection
	TLSRegion string

	// NodeID marks the NodeID that initiated the connection.
	NodeID string
}

// NewClientCodec returns a new rpc.ClientCodec to be used to make RPC calls to
// the Nomad Server.
func NewClientCodec(conn io.ReadWriteCloser) rpc.ClientCodec {
	return msgpackrpc.NewCodecFromHandle(true, true, conn, structs.HashiMsgpackHandle)
}

// NewServerCodec returns a new rpc.ServerCodec to be used by the Nomad Server
// to handle rpcs.
func NewServerCodec(conn io.ReadWriteCloser) rpc.ServerCodec {
	return msgpackrpc.NewCodecFromHandle(true, true, conn, structs.HashiMsgpackHandle)
}

// listen is used to listen for incoming RPC connections
func (s *Server) listen(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			s.logger.Println("[INFO] nomad.rpc: Closing server RPC connection")
			return
		default:
		}

		// Accept a connection
		conn, err := s.rpcListener.Accept()
		if err != nil {
			if s.shutdown {
				return
			}

			select {
			case <-ctx.Done():
				return
			default:
			}

			s.logger.Printf("[ERR] nomad.rpc: failed to accept RPC conn: %v", err)
			continue
		}

		go s.handleConn(ctx, conn, &RPCContext{Conn: conn})
		metrics.IncrCounter([]string{"nomad", "rpc", "accept_conn"}, 1)
	}
}

// handleConn is used to determine if this is a Raft or
// Nomad type RPC connection and invoke the correct handler
func (s *Server) handleConn(ctx context.Context, conn net.Conn, rpcCtx *RPCContext) {
	// Read a single byte
	buf := make([]byte, 1)
	if _, err := conn.Read(buf); err != nil {
		if err != io.EOF {
			s.logger.Printf("[ERR] nomad.rpc: failed to read byte: %v", err)
		}
		conn.Close()
		return
	}

	// Enforce TLS if EnableRPC is set
	if s.config.TLSConfig.EnableRPC && !rpcCtx.TLS && RPCType(buf[0]) != rpcTLS {
		if !s.config.TLSConfig.RPCUpgradeMode {
			s.logger.Printf("[WARN] nomad.rpc: Non-TLS connection attempted from %s with RequireTLS set", conn.RemoteAddr().String())
			conn.Close()
			return
		}
	}

	// Switch on the byte
	switch RPCType(buf[0]) {
	case rpcNomad:
		// Create an RPC Server and handle the request
		server := rpc.NewServer()
		s.setupRpcServer(server, rpcCtx)
		s.handleNomadConn(ctx, conn, server)

		// Remove any potential mapping between a NodeID to this connection and
		// close the underlying connection.
		s.removeNodeConn(rpcCtx)

	case rpcRaft:
		metrics.IncrCounter([]string{"nomad", "rpc", "raft_handoff"}, 1)
		s.raftLayer.Handoff(ctx, conn)

	case rpcMultiplex:
		s.handleMultiplex(ctx, conn, rpcCtx)

	case rpcTLS:
		if s.rpcTLS == nil {
			s.logger.Printf("[WARN] nomad.rpc: TLS connection attempted, server not configured for TLS")
			conn.Close()
			return
		}
		conn = tls.Server(conn, s.rpcTLS)

		// Force a handshake so we can get information about the TLS connection
		// state.
		tlsConn, ok := conn.(*tls.Conn)
		if !ok {
			s.logger.Printf("[ERR] nomad.rpc: expected TLS connection but got %T", conn)
			conn.Close()
			return
		}

		if err := tlsConn.Handshake(); err != nil {
			s.logger.Printf("[WARN] nomad.rpc: failed TLS handshake from connection from %v: %v", tlsConn.RemoteAddr(), err)
			conn.Close()
			return
		}

		// Update the connection context with the fact that the connection is
		// using TLS
		rpcCtx.TLS = true

		// Parse the region and role from the TLS certificate
		state := tlsConn.ConnectionState()
		parts := strings.SplitN(state.ServerName, ".", 3)
		if len(parts) != 3 || (parts[0] != "server" && parts[0] != "client") || parts[2] != "nomad" {
			s.logger.Printf("[WARN] nomad.rpc: invalid server name %q on verified TLS connection", state.ServerName)
		} else {
			rpcCtx.TLSRole = parts[0]
			rpcCtx.TLSRegion = parts[1]
		}

		s.handleConn(ctx, conn, rpcCtx)

	default:
		s.logger.Printf("[ERR] nomad.rpc: unrecognized RPC byte: %v", buf[0])
		conn.Close()
		return
	}
}

// handleMultiplex is used to multiplex a single incoming connection
// using the Yamux multiplexer
func (s *Server) handleMultiplex(ctx context.Context, conn net.Conn, rpcCtx *RPCContext) {
	defer func() {
		// Remove any potential mapping between a NodeID to this connection and
		// close the underlying connection.
		s.removeNodeConn(rpcCtx)
		conn.Close()
	}()

	conf := yamux.DefaultConfig()
	conf.LogOutput = s.config.LogOutput
	server, _ := yamux.Server(conn, conf)

	// Update the context to store the yamux session
	rpcCtx.Session = server

	// Create the RPC server for this connection
	rpcServer := rpc.NewServer()
	s.setupRpcServer(rpcServer, rpcCtx)

	for {
		sub, err := server.Accept()
		if err != nil {
			if err != io.EOF {
				s.logger.Printf("[ERR] nomad.rpc: multiplex conn accept failed: %v", err)
			}
			return
		}
		go s.handleNomadConn(ctx, sub, rpcServer)
	}
}

// handleNomadConn is used to service a single Nomad RPC connection
func (s *Server) handleNomadConn(ctx context.Context, conn net.Conn, server *rpc.Server) {
	defer conn.Close()
	rpcCodec := NewServerCodec(conn)
	for {
		select {
		case <-ctx.Done():
			s.logger.Println("[INFO] nomad.rpc: Closing server RPC connection")
			return
		case <-s.shutdownCh:
			return
		default:
		}

		if err := server.ServeRequest(rpcCodec); err != nil {
			if err != io.EOF && !strings.Contains(err.Error(), "closed") {
				s.logger.Printf("[ERR] nomad.rpc: RPC error: %v (%v)", err, conn)
				metrics.IncrCounter([]string{"nomad", "rpc", "request_error"}, 1)
			}
			return
		}
		metrics.IncrCounter([]string{"nomad", "rpc", "request"}, 1)
	}
}

// forward is used to forward to a remote region or to forward to the local leader
// Returns a bool of if forwarding was performed, as well as any error
func (s *Server) forward(method string, info structs.RPCInfo, args interface{}, reply interface{}) (bool, error) {
	var firstCheck time.Time

	region := info.RequestRegion()
	if region == "" {
		return true, fmt.Errorf("missing target RPC")
	}

	// Handle region forwarding
	if region != s.config.Region {
		err := s.forwardRegion(region, method, args, reply)
		return true, err
	}

	// Check if we can allow a stale read
	if info.IsRead() && info.AllowStaleRead() {
		return false, nil
	}

CHECK_LEADER:
	// Find the leader
	isLeader, remoteServer := s.getLeader()

	// Handle the case we are the leader
	if isLeader {
		return false, nil
	}

	// Handle the case of a known leader
	if remoteServer != nil {
		err := s.forwardLeader(remoteServer, method, args, reply)
		return true, err
	}

	// Gate the request until there is a leader
	if firstCheck.IsZero() {
		firstCheck = time.Now()
	}
	if time.Now().Sub(firstCheck) < s.config.RPCHoldTimeout {
		jitter := lib.RandomStagger(s.config.RPCHoldTimeout / jitterFraction)
		select {
		case <-time.After(jitter):
			goto CHECK_LEADER
		case <-s.shutdownCh:
		}
	}

	// No leader found and hold time exceeded
	return true, structs.ErrNoLeader
}

// getLeader returns if the current node is the leader, and if not
// then it returns the leader which is potentially nil if the cluster
// has not yet elected a leader.
func (s *Server) getLeader() (bool, *serverParts) {
	// Check if we are the leader
	if s.IsLeader() {
		return true, nil
	}

	// Get the leader
	leader := s.raft.Leader()
	if leader == "" {
		return false, nil
	}

	// Lookup the server
	s.peerLock.RLock()
	server := s.localPeers[leader]
	s.peerLock.RUnlock()

	// Server could be nil
	return false, server
}

// forwardLeader is used to forward an RPC call to the leader, or fail if no leader
func (s *Server) forwardLeader(server *serverParts, method string, args interface{}, reply interface{}) error {
	// Handle a missing server
	if server == nil {
		return structs.ErrNoLeader
	}
	return s.connPool.RPC(s.config.Region, server.Addr, server.MajorVersion, method, args, reply)
}

// forwardRegion is used to forward an RPC call to a remote region, or fail if no servers
func (s *Server) forwardRegion(region, method string, args interface{}, reply interface{}) error {
	// Bail if we can't find any servers
	s.peerLock.RLock()
	servers := s.peers[region]
	if len(servers) == 0 {
		s.peerLock.RUnlock()
		s.logger.Printf("[WARN] nomad.rpc: RPC request for region '%s', no path found",
			region)
		return structs.ErrNoRegionPath
	}

	// Select a random addr
	offset := rand.Intn(len(servers))
	server := servers[offset]
	s.peerLock.RUnlock()

	// Forward to remote Nomad
	metrics.IncrCounter([]string{"nomad", "rpc", "cross-region", region}, 1)
	return s.connPool.RPC(region, server.Addr, server.MajorVersion, method, args, reply)
}

// raftApplyFuture is used to encode a message, run it through raft, and return the Raft future.
func (s *Server) raftApplyFuture(t structs.MessageType, msg interface{}) (raft.ApplyFuture, error) {
	buf, err := structs.Encode(t, msg)
	if err != nil {
		return nil, fmt.Errorf("Failed to encode request: %v", err)
	}

	// Warn if the command is very large
	if n := len(buf); n > raftWarnSize {
		s.logger.Printf("[WARN] nomad: Attempting to apply large raft entry (type %d) (%d bytes)", t, n)
	}

	future := s.raft.Apply(buf, enqueueLimit)
	return future, nil
}

// raftApplyFn is the function signature for applying a msg to Raft
type raftApplyFn func(t structs.MessageType, msg interface{}) (interface{}, uint64, error)

// raftApply is used to encode a message, run it through raft, and return
// the FSM response along with any errors
func (s *Server) raftApply(t structs.MessageType, msg interface{}) (interface{}, uint64, error) {
	future, err := s.raftApplyFuture(t, msg)
	if err != nil {
		return nil, 0, err
	}
	if err := future.Error(); err != nil {
		return nil, 0, err
	}
	return future.Response(), future.Index(), nil
}

// setQueryMeta is used to populate the QueryMeta data for an RPC call
func (s *Server) setQueryMeta(m *structs.QueryMeta) {
	if s.IsLeader() {
		m.LastContact = 0
		m.KnownLeader = true
	} else {
		m.LastContact = time.Now().Sub(s.raft.LastContact())
		m.KnownLeader = (s.raft.Leader() != "")
	}
}

// queryFn is used to perform a query operation. If a re-query is needed, the
// passed-in watch set will be used to block for changes. The passed-in state
// store should be used (vs. calling fsm.State()) since the given state store
// will be correctly watched for changes if the state store is restored from
// a snapshot.
type queryFn func(memdb.WatchSet, *state.StateStore) error

// blockingOptions is used to parameterize blockingRPC
type blockingOptions struct {
	queryOpts *structs.QueryOptions
	queryMeta *structs.QueryMeta
	run       queryFn
}

// blockingRPC is used for queries that need to wait for a
// minimum index. This is used to block and wait for changes.
func (s *Server) blockingRPC(opts *blockingOptions) error {
	ctx := context.Background()
	var cancel context.CancelFunc
	var state *state.StateStore

	// Fast path non-blocking
	if opts.queryOpts.MinQueryIndex == 0 {
		goto RUN_QUERY
	}

	// Restrict the max query time, and ensure there is always one
	if opts.queryOpts.MaxQueryTime > maxQueryTime {
		opts.queryOpts.MaxQueryTime = maxQueryTime
	} else if opts.queryOpts.MaxQueryTime <= 0 {
		opts.queryOpts.MaxQueryTime = defaultQueryTime
	}

	// Apply a small amount of jitter to the request
	opts.queryOpts.MaxQueryTime += lib.RandomStagger(opts.queryOpts.MaxQueryTime / jitterFraction)

	// Setup a query timeout
	ctx, cancel = context.WithTimeout(context.Background(), opts.queryOpts.MaxQueryTime)
	defer cancel()

RUN_QUERY:
	// Update the query meta data
	s.setQueryMeta(opts.queryMeta)

	// Increment the rpc query counter
	metrics.IncrCounter([]string{"nomad", "rpc", "query"}, 1)

	// We capture the state store and its abandon channel but pass a snapshot to
	// the blocking query function. We operate on the snapshot to allow separate
	// calls to the state store not all wrapped within the same transaction.
	state = s.fsm.State()
	abandonCh := state.AbandonCh()
	snap, _ := state.Snapshot()
	stateSnap := &snap.StateStore

	// We can skip all watch tracking if this isn't a blocking query.
	var ws memdb.WatchSet
	if opts.queryOpts.MinQueryIndex > 0 {
		ws = memdb.NewWatchSet()

		// This channel will be closed if a snapshot is restored and the
		// whole state store is abandoned.
		ws.Add(abandonCh)
	}

	// Block up to the timeout if we didn't see anything fresh.
	err := opts.run(ws, stateSnap)

	// Check for minimum query time
	if err == nil && opts.queryOpts.MinQueryIndex > 0 && opts.queryMeta.Index <= opts.queryOpts.MinQueryIndex {
		if err := ws.WatchCtx(ctx); err == nil {
			goto RUN_QUERY
		}
	}
	return err
}