package main

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"time"

	"github.com/nats-io/nats.go"
	"github.com/redis/go-redis/v9"
	_ "github.com/taosdata/driver-go/v3/taosWS"

	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/health"
	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/history"
	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/metrics"
	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/observability"
	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/realtime"
	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/topics"
)

func main() {
	logger := observability.NewLogger("nats-fast-writer")
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	cfg := loadConfig()
	conn, err := nats.Connect(cfg.NATSURL, nats.Name(cfg.NATSClientName), nats.Timeout(5*time.Second))
	if err != nil {
		logger.Error("nats connect failed", "error", err)
		os.Exit(1)
	}
	defer conn.Close()
	js, err := conn.JetStream()
	if err != nil {
		logger.Error("nats jetstream init failed", "error", err)
		os.Exit(1)
	}
	if err := ensureStream(js, cfg); err != nil {
		logger.Error("nats stream ensure failed", "stream", cfg.NATSStream, "error", err)
		os.Exit(1)
	}
	sub, err := js.PullSubscribe(
		cfg.NATSFilter,
		cfg.NATSDurable,
		nats.BindStream(cfg.NATSStream),
		nats.ManualAck(),
		nats.AckWait(cfg.AckWait),
		nats.MaxDeliver(-1),
	)
	if err != nil {
		logger.Error("nats pull consumer init failed", "stream", cfg.NATSStream, "durable", cfg.NATSDurable, "error", err)
		os.Exit(1)
	}

	tdDB, err := sql.Open(cfg.TDengineDriver, cfg.TDengineDSN)
	if err != nil {
		logger.Error("tdengine open failed", "error", err)
		os.Exit(1)
	}
	defer tdDB.Close()
	tdDB.SetMaxOpenConns(1)
	tdDB.SetMaxIdleConns(1)
	if err := tdDB.PingContext(ctx); err != nil {
		logger.Error("tdengine ping failed", "error", err)
		os.Exit(1)
	}
	historyWriter := history.NewWriter(tdDB)
	if cfg.TDengineEnsureSchema {
		if err := historyWriter.EnsureSchema(ctx, cfg.TDengineDatabase); err != nil {
			logger.Error("tdengine schema bootstrap failed", "error", err)
			os.Exit(1)
		}
	}
	if strings.TrimSpace(cfg.TDengineDatabase) != "" {
		if _, err := tdDB.ExecContext(ctx, "USE "+cfg.TDengineDatabase); err != nil {
			logger.Error("tdengine use database failed", "database", cfg.TDengineDatabase, "error", err)
			os.Exit(1)
		}
	}

	redisClient := redis.NewClient(&redis.Options{
		Addr:     cfg.RedisAddr,
		Username: cfg.RedisUsername,
		Password: cfg.RedisPassword,
		DB:       cfg.RedisDB,
	})
	defer redisClient.Close()
	if err := redisClient.Ping(ctx).Err(); err != nil {
		logger.Error("redis ping failed", "error", err)
		os.Exit(1)
	}
	realtimeRepo := realtime.NewRepository(redisClient, realtime.Config{OnlineTTL: cfg.OnlineTTL})

	registry := metrics.NewRegistry()
	health.Start(ctx, logger, health.NewServer(env("HEALTH_ADDR", ""), "nats-fast-writer", []health.Check{
		{Name: "nats", Check: func(context.Context) error {
			if conn.Status() != nats.CONNECTED {
				return fmt.Errorf("nats status is %s", conn.Status().String())
			}
			return nil
		}},
		{Name: "tdengine", Check: tdDB.PingContext},
		{Name: "redis", Check: func(ctx context.Context) error { return redisClient.Ping(ctx).Err() }},
	}, registry))

	logger.Info("nats fast writer started",
		"stream", cfg.NATSStream,
		"durable", cfg.NATSDurable,
		"filter", cfg.NATSFilter,
		"batch_size", cfg.BatchSize,
		"workers", cfg.Workers,
		"operation_timeout_ms", cfg.OperationWait.Milliseconds())
	for i := 0; i < cfg.Workers; i++ {
		go runFastWorker(ctx, logger, registry, sub, historyWriter, realtimeRepo, cfg)
	}
	<-ctx.Done()
}

type config struct {
	NATSURL              string
	NATSClientName       string
	NATSStream           string
	NATSDurable          string
	NATSFilter           string
	NATSSubjects         []string
	BatchSize            int
	FetchWait            time.Duration
	OperationWait        time.Duration
	AckWait              time.Duration
	StreamMaxAge         time.Duration
	Workers              int
	TDengineDriver       string
	TDengineDSN          string
	TDengineDatabase     string
	TDengineEnsureSchema bool
	RedisAddr            string
	RedisUsername        string
	RedisPassword        string
	RedisDB              int
	OnlineTTL            time.Duration
}

func loadConfig() config {
	subjects := splitCSV(env("NATS_STREAM_SUBJECTS", strings.Join([]string{
		env("NATS_SUBJECT_GB32960_RAW", env("KAFKA_TOPIC_GB32960_RAW", topics.RawGB32960)),
		env("NATS_SUBJECT_JT808_RAW", env("KAFKA_TOPIC_JT808_RAW", topics.RawJT808)),
		env("NATS_SUBJECT_YUTONG_MQTT_RAW", env("KAFKA_TOPIC_YUTONG_MQTT_RAW", topics.RawYutongMQTT)),
		env("NATS_SUBJECT_GB32960_FIELDS", env("KAFKA_TOPIC_GB32960_FIELDS", topics.FieldsGB32960)),
		env("NATS_SUBJECT_JT808_FIELDS", env("KAFKA_TOPIC_JT808_FIELDS", topics.FieldsJT808)),
		env("NATS_SUBJECT_YUTONG_MQTT_FIELDS", env("KAFKA_TOPIC_YUTONG_MQTT_FIELDS", topics.FieldsYutongMQTT)),
	}, ",")))
	return config{
		NATSURL:              env("NATS_URL", "nats://127.0.0.1:4222"),
		NATSClientName:       env("NATS_CLIENT_NAME", "lingniu-nats-fast-writer"),
		NATSStream:           env("NATS_STREAM", "VEHICLE_INGEST"),
		NATSDurable:          env("NATS_DURABLE", "vehicle-fast-writer"),
		NATSFilter:           env("NATS_FILTER", "vehicle.raw.go.>"),
		NATSSubjects:         subjects,
		BatchSize:            envInt("FAST_WRITER_BATCH_SIZE", 100),
		FetchWait:            time.Duration(envInt("FAST_WRITER_FETCH_WAIT_MS", 100)) * time.Millisecond,
		OperationWait:        time.Duration(envInt("FAST_WRITER_OPERATION_TIMEOUT_MS", 100)) * time.Millisecond,
		AckWait:              time.Duration(envInt("NATS_ACK_WAIT_SECONDS", 30)) * time.Second,
		StreamMaxAge:         time.Duration(envInt("NATS_STREAM_MAX_AGE_HOURS", 24)) * time.Hour,
		Workers:              envInt("FAST_WRITER_WORKERS", 8),
		TDengineDriver:       env("TDENGINE_DRIVER", "taosWS"),
		TDengineDSN:          env("TDENGINE_DSN", ""),
		TDengineDatabase:     env("TDENGINE_DATABASE", history.DefaultDatabase),
		TDengineEnsureSchema: env("TDENGINE_ENSURE_SCHEMA", "true") != "false",
		RedisAddr:            env("REDIS_ADDR", "127.0.0.1:6379"),
		RedisUsername:        env("REDIS_USERNAME", ""),
		RedisPassword:        env("REDIS_PASSWORD", ""),
		RedisDB:              envInt("REDIS_DB", 0),
		OnlineTTL:            time.Duration(envInt("REALTIME_ONLINE_TTL_SECONDS", 60)) * time.Second,
	}
}

type fastAppender interface {
	AppendAll(context.Context, envelope.FrameEnvelope) error
	AppendAllBatch(context.Context, []envelope.FrameEnvelope) error
}

type fastUpdater interface {
	FastUpdate(context.Context, envelope.FrameEnvelope) error
}

type fastMessage struct {
	subject string
	data    []byte
	ack     func() error
}

func runFastWorker(ctx context.Context, logger *slog.Logger, registry *metrics.Registry, sub natsPullSubscription, appender fastAppender, updater fastUpdater, cfg config) {
	for {
		if ctx.Err() != nil {
			return
		}
		msgs, err := sub.Fetch(cfg.BatchSize, nats.MaxWait(cfg.FetchWait))
		if err != nil {
			if errors.Is(err, nats.ErrTimeout) {
				continue
			}
			logger.Error("nats fetch failed", "error", err)
			time.Sleep(time.Second)
			continue
		}
		fastMessages := make([]*fastMessage, 0, len(msgs))
		for _, msg := range msgs {
			natsMsg := msg
			fastMessages = append(fastMessages, &fastMessage{
				subject: natsMsg.Subject,
				data:    natsMsg.Data,
				ack: func() error {
					return natsMsg.Ack()
				},
			})
		}
		operationCtx, cancel := context.WithTimeout(context.WithoutCancel(ctx), cfg.OperationWait)
		err = processFastBatch(operationCtx, registry, appender, updater, fastMessages)
		cancel()
		if err != nil {
			addFastMetric(registry, fastBatchSubject(fastMessages), "error")
			logger.Error("fast write batch failed", "messages", len(fastMessages), "error", err)
			continue
		}
		for _, msg := range fastMessages {
			addFastMetric(registry, msg.subject, "ok")
		}
	}
}

type natsPullSubscription interface {
	Fetch(int, ...nats.PullOpt) ([]*nats.Msg, error)
}

var fastWriterStageDurationBucketsMS = []float64{1, 5, 10, 25, 50, 100, 250, 500, 1000, 5000}

func processFastBatch(ctx context.Context, registry *metrics.Registry, appender fastAppender, updater fastUpdater, messages []*fastMessage) error {
	if len(messages) == 0 {
		return nil
	}
	envelopes := make([]envelope.FrameEnvelope, 0, len(messages))
	validMessages := make([]*fastMessage, 0, len(messages))
	for _, msg := range messages {
		var env envelope.FrameEnvelope
		if err := json.Unmarshal(msg.data, &env); err != nil {
			if msg.ack != nil {
				_ = msg.ack()
			}
			continue
		}
		envelopes = append(envelopes, env)
		validMessages = append(validMessages, msg)
	}
	if len(envelopes) == 0 {
		return nil
	}
	subject := fastBatchSubject(validMessages)
	started := time.Now()
	err := appender.AppendAllBatch(ctx, envelopes)
	recordFastWriterStageDuration(registry, subject, "tdengine", statusFromError(err), time.Since(started))
	if err != nil {
		return fmt.Errorf("tdengine batch append: %w", err)
	}
	for i, env := range envelopes {
		msg := validMessages[i]
		started = time.Now()
		err = updater.FastUpdate(ctx, env)
		recordFastWriterStageDuration(registry, msg.subject, "redis", statusFromError(err), time.Since(started))
		if err != nil {
			return fmt.Errorf("redis fast update: %w", err)
		}
		if msg.ack != nil {
			started = time.Now()
			err = msg.ack()
			recordFastWriterStageDuration(registry, msg.subject, "ack", statusFromError(err), time.Since(started))
			if err != nil {
				return fmt.Errorf("nats ack: %w", err)
			}
		}
	}
	return nil
}

func processFastMessage(ctx context.Context, registry *metrics.Registry, appender fastAppender, updater fastUpdater, msg *fastMessage) error {
	var env envelope.FrameEnvelope
	if err := json.Unmarshal(msg.data, &env); err != nil {
		if msg.ack != nil {
			_ = msg.ack()
		}
		return nil
	}
	started := time.Now()
	err := appender.AppendAll(ctx, env)
	recordFastWriterStageDuration(registry, msg.subject, "tdengine", statusFromError(err), time.Since(started))
	if err != nil {
		return fmt.Errorf("tdengine append: %w", err)
	}
	started = time.Now()
	err = updater.FastUpdate(ctx, env)
	recordFastWriterStageDuration(registry, msg.subject, "redis", statusFromError(err), time.Since(started))
	if err != nil {
		return fmt.Errorf("redis fast update: %w", err)
	}
	if msg.ack != nil {
		started = time.Now()
		err = msg.ack()
		recordFastWriterStageDuration(registry, msg.subject, "ack", statusFromError(err), time.Since(started))
		if err != nil {
			return fmt.Errorf("nats ack: %w", err)
		}
	}
	return nil
}

func fastBatchSubject(messages []*fastMessage) string {
	if len(messages) == 0 {
		return "unknown"
	}
	subject := messages[0].subject
	for _, msg := range messages[1:] {
		if msg.subject != subject {
			return "mixed"
		}
	}
	if strings.TrimSpace(subject) == "" {
		return "unknown"
	}
	return subject
}

func ensureStream(js nats.JetStreamContext, cfg config) error {
	stream := &nats.StreamConfig{
		Name:       cfg.NATSStream,
		Subjects:   cfg.NATSSubjects,
		Storage:    nats.FileStorage,
		Retention:  nats.LimitsPolicy,
		MaxAge:     cfg.StreamMaxAge,
		Duplicates: 2 * time.Minute,
	}
	if _, err := js.StreamInfo(cfg.NATSStream); err == nil {
		_, err = js.UpdateStream(stream)
		return err
	}
	_, err := js.AddStream(stream)
	if err == nil {
		return nil
	}
	_, updateErr := js.UpdateStream(stream)
	if updateErr == nil {
		return nil
	}
	return err
}

func addFastMetric(registry *metrics.Registry, subject string, status string) {
	if registry == nil {
		return
	}
	registry.IncCounter("vehicle_fast_writer_messages_total", metrics.Labels{"subject": subject, "status": status})
}

func recordFastWriterStageDuration(registry *metrics.Registry, subject string, stage string, status string, elapsed time.Duration) {
	if registry == nil {
		return
	}
	registry.ObserveHistogram("vehicle_fast_writer_stage_duration_ms_histogram", metrics.Labels{
		"subject": subject,
		"stage":   stage,
		"status":  status,
	}, fastWriterStageDurationBucketsMS, float64(elapsed.Milliseconds()))
}

func statusFromError(err error) string {
	if err != nil {
		return "error"
	}
	return "ok"
}

func env(key string, fallback string) string {
	value := strings.TrimSpace(os.Getenv(key))
	if value == "" {
		return fallback
	}
	return value
}

func envInt(key string, fallback int) int {
	value := strings.TrimSpace(os.Getenv(key))
	if value == "" {
		return fallback
	}
	var parsed int
	if _, err := fmt.Sscanf(value, "%d", &parsed); err != nil {
		return fallback
	}
	return parsed
}

func splitCSV(value string) []string {
	var out []string
	for _, item := range strings.Split(value, ",") {
		item = strings.TrimSpace(item)
		if item != "" {
			out = append(out, item)
		}
	}
	return out
}