// Package dedup provides idempotent event acceptance via Redis SETNX.
//
// Key shape: dedup:{workspace_id}:{message_id}
// TTL:       24h by default (configurable)
//
// CheckAndSet returns true when the message_id is new (first time seen).
// If it returns false the caller MUST drop the event silently and return 200.
package dedup

import (
	"context"
	"fmt"
	"time"

	"github.com/redis/rueidis"
)

type Dedup interface {
	CheckAndSet(ctx context.Context, workspaceID, messageID string) (bool, error)
}

type redisDedup struct {
	client rueidis.Client
	ttl    time.Duration
}

func New(client rueidis.Client, ttl time.Duration) Dedup {
	return &redisDedup{client: client, ttl: ttl}
}

func key(workspaceID, messageID string) string {
	return fmt.Sprintf("dedup:%s:%s", workspaceID, messageID)
}

func (d *redisDedup) CheckAndSet(ctx context.Context, workspaceID, messageID string) (bool, error) {
	k := key(workspaceID, messageID)
	cmd := d.client.B().Set().Key(k).Value("1").
		Nx().
		Ex(d.ttl).
		Build()
	resp := d.client.Do(ctx, cmd)
	if err := resp.Error(); err != nil {
		return false, fmt.Errorf("dedup setnx: %w", err)
	}
	// SET with NX returns "OK" when set, nil reply when key already exists.
	if resp.IsNil() {
		return false, nil
	}
	return true, nil
}