// Package userlifecycle implements the Redis-Streams consumer for the
// `user:lifecycle_events` topic. wires the consumer behind the
// `ports.UserLifecycleConsumer` interface so the cascade worker can
// register a handler without depending on Redis directly.
//
// The consumer mirrors the reliability shape used by `worker/gmevents`:
// XREAD blocks for `BlockTimeout`, decoded events are dispatched to the
// registered handler, and the persisted offset advances only after the
// handler returns nil. Decoding errors and unknown event kinds are
// logged and absorbed (the offset advances) so a malformed entry never
// stalls the stream. Handler errors hold the offset on the current
// entry so the next loop iteration retries.
package userlifecycle

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"strconv"
	"strings"
	"sync"
	"time"

	"galaxy/lobby/internal/ports"

	"github.com/redis/go-redis/v9"
)

// streamOffsetLabel identifies the user-lifecycle consumer in the
// stream-offset store. It stays stable when the underlying stream key
// is renamed via configuration.
const streamOffsetLabel = "user_lifecycle"

// Config groups the dependencies used by Consumer.
type Config struct {
	// Client provides XREAD access to the user-lifecycle stream.
	Client *redis.Client

	// Stream stores the Redis Streams key consumed by the worker. The
	// production default is `user:lifecycle_events`.
	Stream string

	// BlockTimeout bounds the blocking XREAD window.
	BlockTimeout time.Duration

	// OffsetStore persists the last successfully processed entry id under
	// the `user_lifecycle` label.
	OffsetStore ports.StreamOffsetStore

	// Clock supplies the wall-clock used for log timestamps. Defaults to
	// time.Now when nil.
	Clock func() time.Time

	// Logger receives structured worker-level events. Defaults to
	// slog.Default when nil.
	Logger *slog.Logger
}

// Consumer drives the user-lifecycle processing loop.
type Consumer struct {
	client       *redis.Client
	stream       string
	blockTimeout time.Duration
	offsetStore  ports.StreamOffsetStore
	clock        func() time.Time
	logger       *slog.Logger

	mu      sync.Mutex
	handler ports.UserLifecycleHandler
}

// NewConsumer constructs one Consumer from cfg.
func NewConsumer(cfg Config) (*Consumer, error) {
	switch {
	case cfg.Client == nil:
		return nil, errors.New("new user lifecycle consumer: nil redis client")
	case strings.TrimSpace(cfg.Stream) == "":
		return nil, errors.New("new user lifecycle consumer: stream must not be empty")
	case cfg.BlockTimeout <= 0:
		return nil, errors.New("new user lifecycle consumer: block timeout must be positive")
	case cfg.OffsetStore == nil:
		return nil, errors.New("new user lifecycle consumer: nil offset store")
	}

	clock := cfg.Clock
	if clock == nil {
		clock = time.Now
	}
	logger := cfg.Logger
	if logger == nil {
		logger = slog.Default()
	}

	return &Consumer{
		client:       cfg.Client,
		stream:       cfg.Stream,
		blockTimeout: cfg.BlockTimeout,
		offsetStore:  cfg.OffsetStore,
		clock:        clock,
		logger:       logger.With("worker", "lobby.userlifecycle", "stream", cfg.Stream),
	}, nil
}

// OnEvent installs handler as the sole dispatcher for decoded events.
// A second call replaces the previous handler. Calling OnEvent
// concurrently with Run is safe.
func (consumer *Consumer) OnEvent(handler ports.UserLifecycleHandler) {
	if consumer == nil {
		return
	}
	consumer.mu.Lock()
	consumer.handler = handler
	consumer.mu.Unlock()
}

// Run drives the XREAD loop until ctx is cancelled. The offset advances
// only after a successful handler return so a transient failure replays
// the same entry on the next iteration.
func (consumer *Consumer) Run(ctx context.Context) error {
	if consumer == nil || consumer.client == nil {
		return errors.New("run user lifecycle consumer: nil consumer")
	}
	if ctx == nil {
		return errors.New("run user lifecycle consumer: nil context")
	}
	if err := ctx.Err(); err != nil {
		return err
	}

	lastID, found, err := consumer.offsetStore.Load(ctx, streamOffsetLabel)
	if err != nil {
		return fmt.Errorf("run user lifecycle consumer: load offset: %w", err)
	}
	if !found {
		lastID = "0-0"
	}

	consumer.logger.Info("user lifecycle consumer started",
		"block_timeout", consumer.blockTimeout.String(),
		"start_entry_id", lastID,
	)
	defer consumer.logger.Info("user lifecycle consumer stopped")

	for {
		streams, err := consumer.client.XRead(ctx, &redis.XReadArgs{
			Streams: []string{consumer.stream, lastID},
			Count:   1,
			Block:   consumer.blockTimeout,
		}).Result()
		switch {
		case err == nil:
			for _, stream := range streams {
				for _, message := range stream.Messages {
					if !consumer.handleMessage(ctx, message) {
						continue
					}
					if err := consumer.offsetStore.Save(ctx, streamOffsetLabel, message.ID); err != nil {
						return fmt.Errorf("run user lifecycle consumer: save offset: %w", err)
					}
					lastID = message.ID
				}
			}
		case errors.Is(err, redis.Nil):
			continue
		case ctx.Err() != nil && (errors.Is(err, context.Canceled) || errors.Is(err, context.DeadlineExceeded) || errors.Is(err, redis.ErrClosed)):
			return ctx.Err()
		case errors.Is(err, context.Canceled), errors.Is(err, context.DeadlineExceeded), errors.Is(err, redis.ErrClosed):
			return fmt.Errorf("run user lifecycle consumer: %w", err)
		default:
			return fmt.Errorf("run user lifecycle consumer: %w", err)
		}
	}
}

// Shutdown is a no-op; the consumer relies on context cancellation.
func (consumer *Consumer) Shutdown(ctx context.Context) error {
	if ctx == nil {
		return errors.New("shutdown user lifecycle consumer: nil context")
	}
	return nil
}

// handleMessage decodes one Redis Stream entry and dispatches it to the
// registered handler. It returns true when the offset is allowed to
// advance, false when the consumer must hold the offset and retry on
// the next iteration. Decoding errors and unknown event kinds advance
// the offset so a malformed entry never stalls the stream.
func (consumer *Consumer) handleMessage(ctx context.Context, message redis.XMessage) bool {
	event, err := decodeUserLifecycleEvent(message)
	if err != nil {
		consumer.logger.WarnContext(ctx, "decode user lifecycle event",
			"stream_entry_id", message.ID,
			"err", err.Error(),
		)
		return true
	}
	if !event.EventType.IsKnown() {
		consumer.logger.InfoContext(ctx, "unknown user lifecycle event type",
			"stream_entry_id", message.ID,
			"event_type", event.EventType,
		)
		return true
	}

	consumer.mu.Lock()
	handler := consumer.handler
	consumer.mu.Unlock()

	if handler == nil {
		consumer.logger.WarnContext(ctx, "no user lifecycle handler registered; entry dropped",
			"stream_entry_id", message.ID,
		)
		return true
	}

	if err := handler(ctx, event); err != nil {
		consumer.logger.WarnContext(ctx, "handle user lifecycle event",
			"stream_entry_id", message.ID,
			"event_type", event.EventType,
			"user_id", event.UserID,
			"err", err.Error(),
		)
		return false
	}

	consumer.logger.InfoContext(ctx, "user lifecycle event processed",
		"stream_entry_id", message.ID,
		"event_type", event.EventType,
		"user_id", event.UserID,
	)
	return true
}

func decodeUserLifecycleEvent(message redis.XMessage) (ports.UserLifecycleEvent, error) {
	eventType := optionalString(message.Values, "event_type")
	userID := optionalString(message.Values, "user_id")
	occurredAtRaw := optionalString(message.Values, "occurred_at_ms")

	if strings.TrimSpace(eventType) == "" {
		return ports.UserLifecycleEvent{}, errors.New("missing event_type")
	}
	if strings.TrimSpace(userID) == "" {
		return ports.UserLifecycleEvent{}, errors.New("missing user_id")
	}
	if strings.TrimSpace(occurredAtRaw) == "" {
		return ports.UserLifecycleEvent{}, errors.New("missing occurred_at_ms")
	}

	ms, err := strconv.ParseInt(occurredAtRaw, 10, 64)
	if err != nil {
		return ports.UserLifecycleEvent{}, fmt.Errorf("invalid occurred_at_ms: %w", err)
	}
	if ms <= 0 {
		return ports.UserLifecycleEvent{}, fmt.Errorf("invalid occurred_at_ms: must be positive")
	}

	return ports.UserLifecycleEvent{
		EntryID:    message.ID,
		EventType:  ports.UserLifecycleEventType(eventType),
		UserID:     strings.TrimSpace(userID),
		OccurredAt: time.UnixMilli(ms).UTC(),
		Source:     optionalString(message.Values, "source"),
		ActorType:  optionalString(message.Values, "actor_type"),
		ActorID:    optionalString(message.Values, "actor_id"),
		ReasonCode: optionalString(message.Values, "reason_code"),
		TraceID:    optionalString(message.Values, "trace_id"),
	}, nil
}

func optionalString(values map[string]any, key string) string {
	raw, ok := values[key]
	if !ok {
		return ""
	}
	switch typed := raw.(type) {
	case string:
		return typed
	case []byte:
		return string(typed)
	default:
		return ""
	}
}

// Compile-time assertion: Consumer satisfies the port interface.
var _ ports.UserLifecycleConsumer = (*Consumer)(nil)