package redisstate

import (
	"context"
	"errors"
	"fmt"
	"time"

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

// StreamOffsetStore provides the Redis-backed storage used for persisted
// plain-XREAD consumer progress.
type StreamOffsetStore struct {
	client *redis.Client
	keys   Keyspace
}

// NewStreamOffsetStore constructs one Redis-backed stream-offset store.
func NewStreamOffsetStore(client *redis.Client) (*StreamOffsetStore, error) {
	if client == nil {
		return nil, errors.New("new stream offset store: nil redis client")
	}

	return &StreamOffsetStore{
		client: client,
		keys:   Keyspace{},
	}, nil
}

// Load returns the last processed entry id for stream when one is stored.
func (store *StreamOffsetStore) Load(ctx context.Context, stream string) (string, bool, error) {
	if store == nil || store.client == nil {
		return "", false, errors.New("load stream offset: nil store")
	}
	if ctx == nil {
		return "", false, errors.New("load stream offset: nil context")
	}

	payload, err := store.client.Get(ctx, store.keys.StreamOffset(stream)).Bytes()
	switch {
	case errors.Is(err, redis.Nil):
		return "", false, nil
	case err != nil:
		return "", false, fmt.Errorf("load stream offset: %w", err)
	}

	offset, err := UnmarshalStreamOffset(payload)
	if err != nil {
		return "", false, fmt.Errorf("load stream offset: %w", err)
	}

	return offset.LastProcessedEntryID, true, nil
}

// Save stores the last processed entry id for stream.
func (store *StreamOffsetStore) Save(ctx context.Context, stream string, entryID string) error {
	if store == nil || store.client == nil {
		return errors.New("save stream offset: nil store")
	}
	if ctx == nil {
		return errors.New("save stream offset: nil context")
	}

	offset := StreamOffset{
		Stream:               stream,
		LastProcessedEntryID: entryID,
		UpdatedAt:            time.Now().UTC().Truncate(time.Millisecond),
	}
	payload, err := MarshalStreamOffset(offset)
	if err != nil {
		return fmt.Errorf("save stream offset: %w", err)
	}
	if err := store.client.Set(ctx, store.keys.StreamOffset(stream), payload, 0).Err(); err != nil {
		return fmt.Errorf("save stream offset: %w", err)
	}

	return nil
}