//go:generate ../../../tools/readme_config_includer/generator
package nats

import (
	"bytes"
	"context"
	_ "embed"
	"errors"
	"fmt"
	"os"
	"slices"
	"strings"
	"syscall"
	"text/template"
	"time"

	"github.com/nats-io/nats.go"
	"github.com/nats-io/nats.go/jetstream"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/config"
	"github.com/influxdata/telegraf/plugins/common/tls"
	"github.com/influxdata/telegraf/plugins/outputs"
)

//go:embed sample.conf
var sampleConfig string

type NATS struct {
	Servers        []string      `toml:"servers"`
	Secure         bool          `toml:"secure"`
	Name           string        `toml:"name"`
	Username       config.Secret `toml:"username"`
	Password       config.Secret `toml:"password"`
	Credentials    config.Secret `toml:"credentials"`
	NkeySeed       string        `toml:"nkey_seed"`
	Subject        string        `toml:"subject"`
	UseBatchFormat bool          `toml:"use_batch_format"`
	Jetstream      *StreamConfig `toml:"jetstream"`
	tls.ClientConfig

	Log telegraf.Logger `toml:"-"`

	conn                  *nats.Conn
	jetstreamClient       jetstream.JetStream
	jetstreamStreamConfig *jetstream.StreamConfig
	serializer            telegraf.Serializer
	tplSubject            *template.Template
}

// StreamConfig is the configuration for creating stream
// Almost a mirror of https://pkg.go.dev/github.com/nats-io/nats.go/jetstream#StreamConfig but with TOML tags
type StreamConfig struct {
	Name                  string                            `toml:"name"`
	Description           string                            `toml:"description"`
	Subjects              []string                          `toml:"subjects"`
	Retention             string                            `toml:"retention"`
	MaxConsumers          int                               `toml:"max_consumers"`
	MaxMsgs               int64                             `toml:"max_msgs"`
	MaxBytes              int64                             `toml:"max_bytes"`
	Discard               string                            `toml:"discard"`
	DiscardNewPerSubject  bool                              `toml:"discard_new_per_subject"`
	MaxAge                config.Duration                   `toml:"max_age"`
	MaxMsgsPerSubject     int64                             `toml:"max_msgs_per_subject"`
	MaxMsgSize            int32                             `toml:"max_msg_size"`
	Storage               string                            `toml:"storage"`
	Replicas              int                               `toml:"num_replicas"`
	NoAck                 bool                              `toml:"no_ack"`
	Template              string                            `toml:"template_owner"`
	Duplicates            config.Duration                   `toml:"duplicate_window"`
	Placement             *jetstream.Placement              `toml:"placement"`
	Mirror                *jetstream.StreamSource           `toml:"mirror"`
	Sources               []*jetstream.StreamSource         `toml:"sources"`
	Sealed                bool                              `toml:"sealed"`
	DenyDelete            bool                              `toml:"deny_delete"`
	DenyPurge             bool                              `toml:"deny_purge"`
	AllowRollup           bool                              `toml:"allow_rollup_hdrs"`
	Compression           string                            `toml:"compression"`
	FirstSeq              uint64                            `toml:"first_seq"`
	SubjectTransform      *jetstream.SubjectTransformConfig `toml:"subject_transform"`
	RePublish             *jetstream.RePublish              `toml:"republish"`
	AllowDirect           bool                              `toml:"allow_direct"`
	MirrorDirect          bool                              `toml:"mirror_direct"`
	ConsumerLimits        jetstream.StreamConsumerLimits    `toml:"consumer_limits"`
	Metadata              map[string]string                 `toml:"metadata"`
	AsyncPublish          bool                              `toml:"async_publish"`
	AsyncAckTimeout       *config.Duration                  `toml:"async_ack_timeout"`
	DisableStreamCreation bool                              `toml:"disable_stream_creation"`
}

func (*NATS) SampleConfig() string {
	return sampleConfig
}

func (n *NATS) SetSerializer(serializer telegraf.Serializer) {
	n.serializer = serializer
}

func (n *NATS) Connect() error {
	var err error

	opts := []nats.Option{
		nats.MaxReconnects(-1),
	}

	// override authentication, if any was specified
	if !n.Username.Empty() && !n.Password.Empty() {
		username, err := n.Username.Get()
		if err != nil {
			return fmt.Errorf("getting username failed: %w", err)
		}
		password, err := n.Password.Get()
		if err != nil {
			username.Destroy()
			return fmt.Errorf("getting password failed: %w", err)
		}
		opts = append(opts, nats.UserInfo(username.String(), password.String()))
		username.Destroy()
		password.Destroy()
	}

	if !n.Credentials.Empty() {
		credentialsRaw, secretsErr := n.Credentials.Get()
		if secretsErr != nil {
			return fmt.Errorf("getting credentials secret failed: %w", secretsErr)
		}
		credentials := credentialsRaw.String()
		credentialsRaw.Destroy()

		_, statsErr := os.Stat(credentials)
		if errors.Is(statsErr, os.ErrNotExist) || errors.Is(statsErr, syscall.ENAMETOOLONG) {
			opts = append(opts, nats.UserCredentialBytes([]byte(credentials)))
		} else {
			n.Log.Warn(
				"Using a file for 'credentials' is deprecated since v1.37.0 and will be removed with v1.40.0! " +
					"Use a secret store instead to securely handle your credentials.",
			)
			opts = append(opts, nats.UserCredentials(credentials))
		}
	}

	if n.NkeySeed != "" {
		opt, err := nats.NkeyOptionFromSeed(n.NkeySeed)
		if err != nil {
			return err
		}
		opts = append(opts, opt)
	}

	if n.Name != "" {
		opts = append(opts, nats.Name(n.Name))
	}

	if n.Secure {
		tlsConfig, err := n.ClientConfig.TLSConfig()
		if err != nil {
			return err
		}

		opts = append(opts, nats.Secure(tlsConfig))
	}

	// try and connect
	n.conn, err = nats.Connect(strings.Join(n.Servers, ","), opts...)
	if err != nil {
		return err
	}

	if n.Jetstream != nil {
		n.jetstreamClient, err = jetstream.New(n.conn)
		if err != nil {
			return fmt.Errorf("failed to connect to jetstream: %w", err)
		}

		if n.Jetstream.DisableStreamCreation {
			stream, err := n.jetstreamClient.Stream(context.Background(), n.Jetstream.Name)
			if err != nil {
				if errors.Is(err, nats.ErrStreamNotFound) {
					return fmt.Errorf("stream %q does not exist and disable_stream_creation is true", n.Jetstream.Name)
				}
				return fmt.Errorf("failed to get stream info, name: %s, err: %w", n.Jetstream.Name, err)
			}
			subjects := stream.CachedInfo().Config.Subjects
			n.Log.Infof("Connected to existing stream %q with subjects: %v", n.Jetstream.Name, subjects)
			return nil
		}
		_, err = n.jetstreamClient.CreateOrUpdateStream(context.Background(), *n.jetstreamStreamConfig)
		if err != nil {
			return fmt.Errorf("failed to create or update stream: %w", err)
		}
		n.Log.Infof("Stream %q successfully created or updated", n.Jetstream.Name)
	}
	return nil
}

func (n *NATS) getJetstreamConfig() (*jetstream.StreamConfig, error) {
	var retention jetstream.RetentionPolicy
	switch n.Jetstream.Retention {
	case "", "limits":
		retention = jetstream.LimitsPolicy
	case "interest":
		retention = jetstream.InterestPolicy
	case "workqueue":
		retention = jetstream.WorkQueuePolicy
	default:
		return nil, fmt.Errorf("invalid 'retention' setting %q", n.Jetstream.Retention)
	}

	var discard jetstream.DiscardPolicy
	switch n.Jetstream.Discard {
	case "", "old":
		discard = jetstream.DiscardOld
	case "new":
		discard = jetstream.DiscardNew
	default:
		return nil, fmt.Errorf("invalid 'discard' setting %q", n.Jetstream.Discard)
	}

	var storage jetstream.StorageType
	switch n.Jetstream.Storage {
	case "memory":
		storage = jetstream.MemoryStorage
	case "", "file":
		storage = jetstream.FileStorage
	default:
		return nil, fmt.Errorf("invalid 'storage' setting %q", n.Jetstream.Storage)
	}

	var compression jetstream.StoreCompression
	switch n.Jetstream.Compression {
	case "s2":
		compression = jetstream.S2Compression
	case "", "none":
		compression = jetstream.NoCompression
	default:
		return nil, fmt.Errorf("invalid 'compression' setting %q", n.Jetstream.Compression)
	}

	streamConfig := &jetstream.StreamConfig{
		Name:                 n.Jetstream.Name,
		Description:          n.Jetstream.Description,
		Subjects:             n.Jetstream.Subjects,
		Retention:            retention,
		MaxConsumers:         n.Jetstream.MaxConsumers,
		MaxMsgs:              n.Jetstream.MaxMsgs,
		MaxBytes:             n.Jetstream.MaxBytes,
		Discard:              discard,
		DiscardNewPerSubject: n.Jetstream.DiscardNewPerSubject,
		MaxAge:               time.Duration(n.Jetstream.MaxAge),
		MaxMsgsPerSubject:    n.Jetstream.MaxMsgsPerSubject,
		MaxMsgSize:           n.Jetstream.MaxMsgSize,
		Storage:              storage,
		Replicas:             n.Jetstream.Replicas,
		NoAck:                n.Jetstream.NoAck,
		Template:             n.Jetstream.Template,
		Duplicates:           time.Duration(n.Jetstream.Duplicates),
		Placement:            n.Jetstream.Placement,
		Mirror:               n.Jetstream.Mirror,
		Sources:              n.Jetstream.Sources,
		Sealed:               n.Jetstream.Sealed,
		DenyDelete:           n.Jetstream.DenyDelete,
		DenyPurge:            n.Jetstream.DenyPurge,
		AllowRollup:          n.Jetstream.AllowRollup,
		Compression:          compression,
		FirstSeq:             n.Jetstream.FirstSeq,
		SubjectTransform:     n.Jetstream.SubjectTransform,
		RePublish:            n.Jetstream.RePublish,
		AllowDirect:          n.Jetstream.AllowDirect,
		MirrorDirect:         n.Jetstream.MirrorDirect,
		ConsumerLimits:       n.Jetstream.ConsumerLimits,
		Metadata:             n.Jetstream.Metadata,
	}
	return streamConfig, nil
}

func (n *NATS) Init() error {
	tpl, err := template.New("nats").Parse(n.Subject)
	if err != nil {
		return fmt.Errorf("failed to parse subject template: %w", err)
	}
	n.tplSubject = tpl

	if n.Jetstream == nil {
		return nil
	}

	// JETSTREAM-ONLY code beyond this line
	// Validate stream name
	if strings.TrimSpace(n.Jetstream.Name) == "" {
		return errors.New("stream cannot be empty")
	}

	if n.Jetstream.AsyncAckTimeout == nil {
		to := config.Duration(5 * time.Second)
		n.Jetstream.AsyncAckTimeout = &to
	}
	// Handle dynamic subject case
	var buf bytes.Buffer
	if err := tpl.Execute(&buf, nil); err != nil || buf.String() != n.Subject {
		if len(n.Jetstream.Subjects) > 0 {
			var err error
			n.jetstreamStreamConfig, err = n.getJetstreamConfig()
			return err
		}
		return errors.New("jetstream subjects must be set when using a dynamic subject")
	}

	// JETSTREAM-ONLY and STATIC SUBJECT code beyond this line
	// Append subject if not already included
	if !slices.Contains(n.Jetstream.Subjects, n.Subject) {
		n.Jetstream.Subjects = append(n.Jetstream.Subjects, n.Subject)
	}

	// Generate Jetstream config
	cfg, err := n.getJetstreamConfig()
	if err != nil {
		return fmt.Errorf("failed to parse jetstream config: %w", err)
	}
	n.jetstreamStreamConfig = cfg
	return nil
}

func (n *NATS) Close() error {
	n.conn.Close()
	return nil
}

func (n *NATS) publishMessage(sub string, buf []byte) (jetstream.PubAckFuture, error) {
	if n.Jetstream != nil {
		if n.Jetstream.AsyncPublish {
			paf, err := n.jetstreamClient.PublishAsync(sub, buf, jetstream.WithExpectStream(n.Jetstream.Name))
			return paf, err
		}
		_, err := n.jetstreamClient.Publish(context.Background(), sub, buf, jetstream.WithExpectStream(n.Jetstream.Name))
		return nil, err
	}
	err := n.conn.Publish(sub, buf)
	return nil, err
}

func (n *NATS) Write(metrics []telegraf.Metric) error {
	if len(metrics) == 0 {
		return nil
	}

	msgCount := len(metrics)
	if n.UseBatchFormat {
		msgCount = 1
	}

	var pafs []jetstream.PubAckFuture
	if n.Jetstream != nil && n.Jetstream.AsyncPublish {
		pafs = make([]jetstream.PubAckFuture, msgCount)
	}

	if n.UseBatchFormat {
		buf, err := n.serializer.SerializeBatch(metrics)
		if err != nil {
			n.Log.Debugf("Could not serialize batch of metrics: %v", err)
			return nil
		}
		paf, err := n.publishMessage(n.Subject, buf)
		if err != nil {
			return fmt.Errorf("failed to send NATS message to subject %q: %w", n.Subject, err)
		}
		if n.Jetstream != nil && n.Jetstream.AsyncPublish {
			pafs[0] = paf
		}
	} else {
		var subject bytes.Buffer
		for i, raw := range metrics {
			m := raw
			if wm, ok := m.(telegraf.UnwrappableMetric); ok {
				m = wm.Unwrap()
			}
			subject.Reset()
			if err := n.tplSubject.Execute(&subject, m); err != nil {
				return fmt.Errorf("failed to execute subject template: %w", err)
			}
			sub := subject.String()
			if strings.Contains(sub, "..") || strings.HasSuffix(sub, ".") {
				n.Log.Errorf("invalid subject %q for metric %v", sub, m)
				continue
			}

			buf, err := n.serializer.Serialize(m)
			if err != nil {
				n.Log.Debugf("Could not serialize metric: %v", err)
				continue
			}

			paf, err := n.publishMessage(sub, buf)
			if err != nil {
				return fmt.Errorf("failed to send NATS message: %w", err)
			}

			if n.Jetstream != nil && n.Jetstream.AsyncPublish {
				pafs[i] = paf
			}
		}
	}

	if pafs != nil {
		// Check Ack from async publish
		select {
		case <-n.jetstreamClient.PublishAsyncComplete():
			for i := range pafs {
				select {
				case <-pafs[i].Ok():
					continue
				case err := <-pafs[i].Err():
					return fmt.Errorf("publish acknowledgement is an error: %w (retrying)", err)
				}
			}
		case <-time.After(time.Duration(*n.Jetstream.AsyncAckTimeout)):
			return fmt.Errorf("waiting for acknowledgement timed out, %d messages pending", n.jetstreamClient.PublishAsyncPending())
		}
	}
	return nil
}

func init() {
	outputs.Add("nats", func() telegraf.Output {
		return &NATS{}
	})
}
