// Package lifecycleevents implements the Redis Streams-backed publisher for
// trusted user-lifecycle events consumed by `Game Lobby`.
package lifecycleevents

import (
	"context"
	"errors"
	"fmt"
	"strconv"
	"strings"
	"time"

	"galaxy/user/internal/ports"

	"github.com/redis/go-redis/v9"
	"go.opentelemetry.io/otel/trace"
)

// Config configures one Redis-backed user-lifecycle publisher. The
// connection is supplied externally by the runtime so multiple publishers
// can share one *redis.Client.
type Config struct {
	// Stream identifies the Redis Stream key used for lifecycle events. The
	// default platform key is `user:lifecycle_events`.
	Stream string

	// StreamMaxLen bounds the stream with approximate trimming via
	// `XADD MAXLEN ~`.
	StreamMaxLen int64

	// OperationTimeout bounds each Redis round trip performed by the adapter.
	OperationTimeout time.Duration
}

// Publisher publishes trusted user-lifecycle events into the dedicated Redis
// Stream consumed by `Game Lobby` for Race Name Directory cascade release.
type Publisher struct {
	client           *redis.Client
	stream           string
	streamMaxLen     int64
	operationTimeout time.Duration
}

// New constructs a Redis-backed lifecycle-event publisher backed by the
// supplied client. The publisher does not own the client; the runtime is
// responsible for closing it.
func New(client *redis.Client, cfg Config) (*Publisher, error) {
	switch {
	case client == nil:
		return nil, errors.New("new redis lifecycle-event publisher: redis client must not be nil")
	case strings.TrimSpace(cfg.Stream) == "":
		return nil, errors.New("new redis lifecycle-event publisher: stream must not be empty")
	case cfg.StreamMaxLen <= 0:
		return nil, errors.New("new redis lifecycle-event publisher: stream max len must be positive")
	case cfg.OperationTimeout <= 0:
		return nil, errors.New("new redis lifecycle-event publisher: operation timeout must be positive")
	}

	return &Publisher{
		client:           client,
		stream:           cfg.Stream,
		streamMaxLen:     cfg.StreamMaxLen,
		operationTimeout: cfg.OperationTimeout,
	}, nil
}

// Close is a no-op: the client is owned by the runtime.
func (publisher *Publisher) Close() error {
	return nil
}

// Ping verifies that the configured Redis backend is reachable within the
// adapter operation timeout budget.
func (publisher *Publisher) Ping(ctx context.Context) error {
	operationCtx, cancel, err := publisher.operationContext(ctx, "ping redis lifecycle-event publisher")
	if err != nil {
		return err
	}
	defer cancel()

	if err := publisher.client.Ping(operationCtx).Err(); err != nil {
		return fmt.Errorf("ping redis lifecycle-event publisher: %w", err)
	}

	return nil
}

// PublishUserLifecycleEvent publishes one committed lifecycle event to the
// configured Redis Stream.
func (publisher *Publisher) PublishUserLifecycleEvent(ctx context.Context, event ports.UserLifecycleEvent) error {
	if err := event.Validate(); err != nil {
		return fmt.Errorf("publish user lifecycle event: %w", err)
	}

	traceID := traceIDFromContext(ctx, event.TraceID)

	values := map[string]any{
		"event_type":     string(event.EventType),
		"user_id":        event.UserID.String(),
		"occurred_at_ms": strconv.FormatInt(event.OccurredAt.UTC().UnixMilli(), 10),
		"source":         event.Source.String(),
		"actor_type":     event.Actor.Type.String(),
		"reason_code":    event.ReasonCode.String(),
	}
	if !event.Actor.ID.IsZero() {
		values["actor_id"] = event.Actor.ID.String()
	}
	if traceID != "" {
		values["trace_id"] = traceID
	}

	operationCtx, cancel, err := publisher.operationContext(ctx, "publish user lifecycle event")
	if err != nil {
		return err
	}
	defer cancel()

	if err := publisher.client.XAdd(operationCtx, &redis.XAddArgs{
		Stream: publisher.stream,
		MaxLen: publisher.streamMaxLen,
		Approx: true,
		Values: values,
	}).Err(); err != nil {
		return fmt.Errorf("publish user lifecycle event: %w", err)
	}

	return nil
}

func (publisher *Publisher) operationContext(ctx context.Context, operation string) (context.Context, context.CancelFunc, error) {
	if publisher == nil || publisher.client == nil {
		return nil, nil, fmt.Errorf("%s: nil publisher", operation)
	}
	if ctx == nil {
		return nil, nil, fmt.Errorf("%s: nil context", operation)
	}

	operationCtx, cancel := context.WithTimeout(ctx, publisher.operationTimeout)
	return operationCtx, cancel, nil
}

func traceIDFromContext(ctx context.Context, fallback string) string {
	if strings.TrimSpace(fallback) != "" {
		return fallback
	}
	if ctx == nil {
		return ""
	}

	spanContext := trace.SpanContextFromContext(ctx)
	if !spanContext.IsValid() {
		return ""
	}

	return spanContext.TraceID().String()
}

var (
	_ interface{ Close() error }               = (*Publisher)(nil)
	_ interface{ Ping(context.Context) error } = (*Publisher)(nil)
	_ ports.UserLifecyclePublisher             = (*Publisher)(nil)
)