package cisco_telemetry_mdt

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"io"
	"log"
	"net"
	"strings"
	"sync"
	"time"

	dialout "github.com/cisco-ie/nx-telemetry-proto/mdt_dialout"
	telemetry "github.com/cisco-ie/nx-telemetry-proto/telemetry_bis"
	"github.com/golang/protobuf/proto"
	"github.com/influxdata/telegraf"
	internaltls "github.com/influxdata/telegraf/internal/tls"
	"github.com/influxdata/telegraf/plugins/inputs"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials"
	"google.golang.org/grpc/peer"
)

const (
	// Maximum telemetry payload size (in bytes) to accept for GRPC dialout transport
	tcpMaxMsgLen uint32 = 1024 * 1024
)

// CiscoTelemetryMDT plugin for IOS XR, IOS XE and NXOS platforms
type CiscoTelemetryMDT struct {
	// Common configuration
	Transport      string
	ServiceAddress string            `toml:"service_address"`
	MaxMsgSize     int               `toml:"max_msg_size"`
	Aliases        map[string]string `toml:"aliases"`

	// GRPC TLS settings
	internaltls.ServerConfig

	// Internal listener / client handle
	grpcServer *grpc.Server
	listener   net.Listener

	// Internal state
	aliases map[string]string
	acc     telegraf.Accumulator
	wg      sync.WaitGroup
}

// Start the Cisco MDT service
func (c *CiscoTelemetryMDT) Start(acc telegraf.Accumulator) error {
	var err error
	c.acc = acc
	c.listener, err = net.Listen("tcp", c.ServiceAddress)
	if err != nil {
		return err
	}

	// Invert aliases list
	c.aliases = make(map[string]string, len(c.Aliases))
	for alias, path := range c.Aliases {
		c.aliases[path] = alias
	}

	switch c.Transport {
	case "tcp":
		// TCP dialout server accept routine
		c.wg.Add(1)
		go func() {
			c.acceptTCPClients()
			c.wg.Done()
		}()

	case "grpc":
		var opts []grpc.ServerOption
		tlsConfig, err := c.ServerConfig.TLSConfig()
		if err != nil {
			return err
		} else if tlsConfig != nil {
			opts = append(opts, grpc.Creds(credentials.NewTLS(tlsConfig)))
		}

		if c.MaxMsgSize > 0 {
			opts = append(opts, grpc.MaxRecvMsgSize(c.MaxMsgSize))
		}

		c.grpcServer = grpc.NewServer(opts...)
		dialout.RegisterGRPCMdtDialoutServer(c.grpcServer, c)

		c.wg.Add(1)
		go func() {
			c.grpcServer.Serve(c.listener)
			c.wg.Done()
		}()

	default:
		c.listener.Close()
		return fmt.Errorf("invalid Cisco MDT transport: %s", c.Transport)
	}

	return nil
}

// AcceptTCPDialoutClients defines the TCP dialout server main routine
func (c *CiscoTelemetryMDT) acceptTCPClients() {
	// Keep track of all active connections, so we can close them if necessary
	var mutex sync.Mutex
	clients := make(map[net.Conn]struct{})

	for {
		conn, err := c.listener.Accept()
		if neterr, ok := err.(*net.OpError); ok && (neterr.Timeout() || neterr.Temporary()) {
			continue
		} else if err != nil {
			break // Stop() will close the connection so Accept() will fail here
		}

		mutex.Lock()
		clients[conn] = struct{}{}
		mutex.Unlock()

		// Individual client connection routine
		c.wg.Add(1)
		go func() {
			log.Printf("D! [inputs.cisco_telemetry_mdt]: Accepted Cisco MDT TCP dialout connection from %s", conn.RemoteAddr())
			if err := c.handleTCPClient(conn); err != nil {
				c.acc.AddError(err)
			}
			log.Printf("D! [inputs.cisco_telemetry_mdt]: Closed Cisco MDT TCP dialout connection from %s", conn.RemoteAddr())

			mutex.Lock()
			delete(clients, conn)
			mutex.Unlock()

			conn.Close()
			c.wg.Done()
		}()
	}

	// Close all remaining client connections
	mutex.Lock()
	for client := range clients {
		if err := client.Close(); err != nil {
			log.Printf("E! [inputs.cisco_telemetry_mdt]: Failed to close TCP dialout client: %v", err)
		}
	}
	mutex.Unlock()
}

// Handle a TCP telemetry client
func (c *CiscoTelemetryMDT) handleTCPClient(conn net.Conn) error {
	// TCP Dialout telemetry framing header
	var hdr struct {
		MsgType       uint16
		MsgEncap      uint16
		MsgHdrVersion uint16
		MsgFlags      uint16
		MsgLen        uint32
	}

	var payload bytes.Buffer

	for {
		// Read and validate dialout telemetry header
		if err := binary.Read(conn, binary.BigEndian, &hdr); err != nil {
			return err
		}

		maxMsgSize := tcpMaxMsgLen
		if c.MaxMsgSize > 0 {
			maxMsgSize = uint32(c.MaxMsgSize)
		}

		if hdr.MsgLen > maxMsgSize {
			return fmt.Errorf("dialout packet too long: %v", hdr.MsgLen)
		} else if hdr.MsgFlags != 0 {
			return fmt.Errorf("invalid dialout flags: %v", hdr.MsgFlags)
		}

		// Read and handle telemetry packet
		payload.Reset()
		if size, err := payload.ReadFrom(io.LimitReader(conn, int64(hdr.MsgLen))); size != int64(hdr.MsgLen) {
			if err != nil {
				return err
			}
			return fmt.Errorf("TCP dialout premature EOF")
		}

		c.handleTelemetry(payload.Bytes())
	}
}

// MdtDialout RPC server method for grpc-dialout transport
func (c *CiscoTelemetryMDT) MdtDialout(stream dialout.GRPCMdtDialout_MdtDialoutServer) error {
	peer, peerOK := peer.FromContext(stream.Context())
	if peerOK {
		log.Printf("D! [inputs.cisco_telemetry_mdt]: Accepted Cisco MDT GRPC dialout connection from %s", peer.Addr)
	}

	for {
		packet, err := stream.Recv()
		if err != nil {
			if err != io.EOF {
				c.acc.AddError(fmt.Errorf("GRPC dialout receive error: %v", err))
			}
			break
		}

		if len(packet.Data) == 0 && len(packet.Errors) != 0 {
			c.acc.AddError(fmt.Errorf("GRPC dialout error: %s", packet.Errors))
			break
		}

		c.handleTelemetry(packet.Data)
	}

	if peerOK {
		log.Printf("D! [inputs.cisco_telemetry_mdt]: Closed Cisco MDT GRPC dialout connection from %s", peer.Addr)
	}

	return nil
}

// Handle telemetry packet from any transport, decode and add as measurement
func (c *CiscoTelemetryMDT) handleTelemetry(data []byte) {
	var namebuf bytes.Buffer
	telemetry := &telemetry.Telemetry{}
	err := proto.Unmarshal(data, telemetry)
	if err != nil {
		c.acc.AddError(fmt.Errorf("Cisco MDT failed to decode: %v", err))
		return
	}

	for _, gpbkv := range telemetry.DataGpbkv {
		var fields map[string]interface{}

		// Produce metadata tags
		var tags map[string]string

		// Top-level field may have measurement timestamp, if not use message timestamp
		measured := gpbkv.Timestamp
		if measured == 0 {
			measured = telemetry.MsgTimestamp
		}

		timestamp := time.Unix(int64(measured/1000), int64(measured%1000)*1000000)

		// Populate tags and fields from toplevel GPBKV fields "keys" and "content"
		for _, field := range gpbkv.Fields {
			switch field.Name {
			case "keys":
				tags = make(map[string]string, len(field.Fields)+2)
				tags["source"] = telemetry.GetNodeIdStr()
				tags["subscription"] = telemetry.GetSubscriptionIdStr()
				for _, subfield := range field.Fields {
					c.parseGPBKVField(subfield, &namebuf, telemetry.EncodingPath, timestamp, tags, nil)
				}
			case "content":
				fields = make(map[string]interface{}, len(field.Fields))
				for _, subfield := range field.Fields {
					c.parseGPBKVField(subfield, &namebuf, telemetry.EncodingPath, timestamp, tags, fields)
				}
			default:
				log.Printf("I! [inputs.cisco_telemetry_mdt]: Unexpected top-level MDT field: %s", field.Name)
			}
		}

		// Find best alias for encoding path and emit measurement
		if len(fields) > 0 && len(tags) > 0 && len(telemetry.EncodingPath) > 0 {
			name := telemetry.EncodingPath
			if alias, ok := c.aliases[name]; ok {
				tags["path"] = name
				name = alias
			} else {
				log.Printf("D! [inputs.cisco_telemetry_mdt]: No measurement alias for encoding path: %s", name)
			}
			c.acc.AddFields(name, fields, tags, timestamp)
		} else {
			c.acc.AddError(fmt.Errorf("empty encoding path or measurement"))
		}
	}
}

// Recursively parse GPBKV field structure into fields or tags
func (c *CiscoTelemetryMDT) parseGPBKVField(field *telemetry.TelemetryField, namebuf *bytes.Buffer,
	path string, timestamp time.Time, tags map[string]string, fields map[string]interface{}) {

	namelen := namebuf.Len()
	if namelen > 0 {
		namebuf.WriteRune('/')
	}
	namebuf.WriteString(strings.Replace(field.Name, "-", "_", -1))

	// Decode Telemetry field value if set
	var value interface{}
	switch val := field.ValueByType.(type) {
	case *telemetry.TelemetryField_BytesValue:
		value = val.BytesValue
	case *telemetry.TelemetryField_StringValue:
		value = val.StringValue
	case *telemetry.TelemetryField_BoolValue:
		value = val.BoolValue
	case *telemetry.TelemetryField_Uint32Value:
		value = val.Uint32Value
	case *telemetry.TelemetryField_Uint64Value:
		value = val.Uint64Value
	case *telemetry.TelemetryField_Sint32Value:
		value = val.Sint32Value
	case *telemetry.TelemetryField_Sint64Value:
		value = val.Sint64Value
	case *telemetry.TelemetryField_DoubleValue:
		value = val.DoubleValue
	case *telemetry.TelemetryField_FloatValue:
		value = val.FloatValue
	}

	if value != nil {
		// Distinguish between tags (keys) and fields (data) to write to
		if fields != nil {
			fields[namebuf.String()] = value
		} else {
			if _, exists := tags[field.Name]; !exists { // Use short keys whenever possible
				tags[field.Name] = fmt.Sprint(value)
			} else {
				tags[namebuf.String()] = fmt.Sprint(value)
			}
		}
	}

	for _, subfield := range field.Fields {
		c.parseGPBKVField(subfield, namebuf, path, timestamp, tags, fields)
	}

	namebuf.Truncate(namelen)
}

// Stop listener and cleanup
func (c *CiscoTelemetryMDT) Stop() {
	if c.grpcServer != nil {
		// Stop server and terminate all running dialout routines
		c.grpcServer.Stop()
	}
	if c.listener != nil {
		c.listener.Close()
	}
	c.wg.Wait()
}

const sampleConfig = `
 ## Telemetry transport (one of: tcp, grpc)
 transport = "grpc"

 ## Address and port to host telemetry listener
 service_address = ":57000"

 ## Enable TLS for GRPC transport
 # tls_cert = "/etc/telegraf/cert.pem"
 # tls_key = "/etc/telegraf/key.pem"

 ## Enable TLS client authentication and define allowed CA certificates
 # tls_allowed_cacerts = ["/etc/telegraf/clientca.pem"]

 ## Define aliases to map telemetry encoding paths to simple measurement names
 [inputs.cisco_telemetry_mdt.aliases]
   ifstats = "ietf-interfaces:interfaces-state/interface/statistics"
`

// SampleConfig of plugin
func (c *CiscoTelemetryMDT) SampleConfig() string {
	return sampleConfig
}

// Description of plugin
func (c *CiscoTelemetryMDT) Description() string {
	return "Cisco model-driven telemetry (MDT) input plugin for IOS XR, IOS XE and NX-OS platforms"
}

// Gather plugin measurements (unused)
func (c *CiscoTelemetryMDT) Gather(_ telegraf.Accumulator) error {
	return nil
}

func init() {
	inputs.Add("cisco_telemetry_mdt", func() telegraf.Input {
		return &CiscoTelemetryMDT{
			Transport:      "grpc",
			ServiceAddress: "127.0.0.1:57000",
		}
	})
}