package nomad

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"io"
	"net"
	"time"

	log "github.com/hashicorp/go-hclog"
	sframer "github.com/hashicorp/nomad/client/lib/streamframer"
	cstructs "github.com/hashicorp/nomad/client/structs"
	"github.com/hashicorp/nomad/command/agent/monitor"
	"github.com/hashicorp/nomad/helper"
	"github.com/hashicorp/nomad/nomad/structs"

	"github.com/ugorji/go/codec"
)

type Agent struct {
	srv *Server
}

func (m *Agent) register() {
	m.srv.streamingRpcs.Register("Agent.Monitor", m.monitor)
}

func (m *Agent) monitor(conn io.ReadWriteCloser) {
	defer conn.Close()

	// Decode args
	var args cstructs.MonitorRequest
	decoder := codec.NewDecoder(conn, structs.MsgpackHandle)
	encoder := codec.NewEncoder(conn, structs.MsgpackHandle)

	if err := decoder.Decode(&args); err != nil {
		handleStreamResultError(err, helper.Int64ToPtr(500), encoder)
		return
	}

	// Check agent read permissions
	if aclObj, err := m.srv.ResolveToken(args.AuthToken); err != nil {
		handleStreamResultError(err, nil, encoder)
		return
	} else if aclObj != nil && !aclObj.AllowAgentRead() {
		handleStreamResultError(structs.ErrPermissionDenied, helper.Int64ToPtr(403), encoder)
		return
	}

	logLevel := log.LevelFromString(args.LogLevel)
	if args.LogLevel == "" {
		logLevel = log.LevelFromString("INFO")
	}

	if logLevel == log.NoLevel {
		handleStreamResultError(errors.New("Unknown log level"), helper.Int64ToPtr(400), encoder)
		return
	}

	// Targeting a node, forward request to node
	if args.NodeID != "" {
		m.forwardMonitorClient(conn, args, encoder, decoder)
		// forwarded request has ended, return
		return
	}

	currentServer := m.srv.serf.LocalMember().Name
	var forwardServer bool
	// Targeting a remote server which is not the leader and not this server
	if args.ServerID != "" && args.ServerID != "leader" && args.ServerID != currentServer {
		forwardServer = true
	}

	// Targeting leader and this server is not current leader
	if args.ServerID == "leader" && !m.srv.IsLeader() {
		forwardServer = true
	}

	if forwardServer {
		m.forwardMonitorServer(conn, args, encoder, decoder)
		return
	}

	// NodeID was empty, so monitor this current server
	ctx, cancel := context.WithCancel(context.Background())
	defer cancel()

	monitor := monitor.New(512, m.srv.logger, &log.LoggerOptions{
		Level:      logLevel,
		JSONFormat: args.LogJSON,
	})

	frames := make(chan *sframer.StreamFrame, 32)
	errCh := make(chan error)
	var buf bytes.Buffer
	frameCodec := codec.NewEncoder(&buf, structs.JsonHandle)

	framer := sframer.NewStreamFramer(frames, 1*time.Second, 200*time.Millisecond, 1024)
	framer.Run()
	defer framer.Destroy()

	// goroutine to detect remote side closing
	go func() {
		if _, err := conn.Read(nil); err != nil {
			// One end of the pipe explicitly closed, exit
			cancel()
			return
		}
		select {
		case <-ctx.Done():
			return
		}
	}()

	logCh := monitor.Start()
	defer monitor.Stop()
	initialOffset := int64(0)

	// receive logs and build frames
	go func() {
		defer framer.Destroy()
	LOOP:
		for {
			select {
			case log := <-logCh:
				if err := framer.Send("", "log", log, initialOffset); err != nil {
					select {
					case errCh <- err:
					case <-ctx.Done():
					}
					break LOOP
				}
			case <-ctx.Done():
				break LOOP
			}
		}
	}()

	var streamErr error
OUTER:
	for {
		select {
		case frame, ok := <-frames:
			if !ok {
				// frame may have been closed when an error
				// occurred. Check once more for an error.
				select {
				case streamErr = <-errCh:
					// There was a pending error!
				default:
					// No error, continue on
				}

				break OUTER
			}

			var resp cstructs.StreamErrWrapper
			if args.PlainText {
				resp.Payload = frame.Data
			} else {
				if err := frameCodec.Encode(frame); err != nil {
					streamErr = err
					break OUTER
				}

				resp.Payload = buf.Bytes()
				buf.Reset()
			}

			if err := encoder.Encode(resp); err != nil {
				streamErr = err
				break OUTER
			}
			encoder.Reset(conn)
		case <-ctx.Done():
			break OUTER
		}
	}

	if streamErr != nil {
		handleStreamResultError(streamErr, helper.Int64ToPtr(500), encoder)
		return
	}
}

func (m *Agent) forwardMonitorClient(conn io.ReadWriteCloser, args cstructs.MonitorRequest, encoder *codec.Encoder, decoder *codec.Decoder) {
	nodeID := args.NodeID

	snap, err := m.srv.State().Snapshot()
	if err != nil {
		handleStreamResultError(err, nil, encoder)
		return
	}

	node, err := snap.NodeByID(nil, nodeID)
	if err != nil {
		handleStreamResultError(err, helper.Int64ToPtr(500), encoder)
		return
	}

	if node == nil {
		err := fmt.Errorf("Unknown node %q", nodeID)
		handleStreamResultError(err, helper.Int64ToPtr(400), encoder)
		return
	}

	if err := nodeSupportsRpc(node); err != nil {
		handleStreamResultError(err, helper.Int64ToPtr(400), encoder)
		return
	}

	// Get the Connection to the client either by fowarding to another server
	// or creating direct stream
	var clientConn net.Conn
	state, ok := m.srv.getNodeConn(nodeID)
	if !ok {
		// Determine the server that has a connection to the node
		srv, err := m.srv.serverWithNodeConn(nodeID, m.srv.Region())
		if err != nil {
			var code *int64
			if structs.IsErrNoNodeConn(err) {
				code = helper.Int64ToPtr(404)
			}
			handleStreamResultError(err, code, encoder)
			return
		}
		conn, err := m.srv.streamingRpc(srv, "Agent.Monitor")
		if err != nil {
			handleStreamResultError(err, nil, encoder)
			return
		}

		clientConn = conn
	} else {
		stream, err := NodeStreamingRpc(state.Session, "Agent.Monitor")
		if err != nil {
			handleStreamResultError(err, nil, encoder)
			return
		}
		clientConn = stream
	}
	defer clientConn.Close()

	// Send the Request
	outEncoder := codec.NewEncoder(clientConn, structs.MsgpackHandle)
	if err := outEncoder.Encode(args); err != nil {
		handleStreamResultError(err, nil, encoder)
		return
	}

	structs.Bridge(conn, clientConn)
	return
}

func (m *Agent) forwardMonitorServer(conn io.ReadWriteCloser, args cstructs.MonitorRequest, encoder *codec.Encoder, decoder *codec.Decoder) {
	var target *serverParts
	serverID := args.ServerID

	// empty ServerID to prevent forwarding loop
	args.ServerID = ""

	if serverID == "leader" {
		isLeader, remoteServer := m.srv.getLeader()
		if !isLeader && remoteServer != nil {
			target = remoteServer
		}
		if !isLeader && remoteServer == nil {
			handleStreamResultError(structs.ErrNoLeader, helper.Int64ToPtr(400), encoder)
			return
		}
	} else {
		// See if the server ID is a known member
		serfMembers := m.srv.Members()
		for _, mem := range serfMembers {
			if mem.Name == serverID {
				if ok, srv := isNomadServer(mem); ok {
					target = srv
				}
			}
		}
	}

	// Unable to find a server
	if target == nil {
		err := fmt.Errorf("unknown nomad server %s", serverID)
		handleStreamResultError(err, helper.Int64ToPtr(400), encoder)
		return
	}

	serverConn, err := m.srv.streamingRpc(target, "Agent.Monitor")
	if err != nil {
		handleStreamResultError(err, helper.Int64ToPtr(500), encoder)
		return
	}
	defer serverConn.Close()

	// Send the Request
	outEncoder := codec.NewEncoder(serverConn, structs.MsgpackHandle)
	if err := outEncoder.Encode(args); err != nil {
		handleStreamResultError(err, helper.Int64ToPtr(500), encoder)
		return
	}

	structs.Bridge(conn, serverConn)
	return
}