// Package storage provides storage abstractions for datasets and transfer tracking.
package storage

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

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

// DatasetInfo contains information about a dataset.
type DatasetInfo struct {
	LastAccess time.Time `json:"last_access"`
	Name       string    `json:"name"`
	Location   string    `json:"location"`
	SizeBytes  int64     `json:"size_bytes"`
}

// DatasetStore manages dataset metadata and transfer tracking.
type DatasetStore struct {
	client redis.UniversalClient
	ctx    context.Context
}

// NewDatasetStore creates a new DatasetStore with the given Redis client.
func NewDatasetStore(client redis.UniversalClient) *DatasetStore {
	return &DatasetStore{
		client: client,
		ctx:    context.Background(),
	}
}

// NewDatasetStoreWithContext creates a new DatasetStore with a custom context.
func NewDatasetStoreWithContext(client redis.UniversalClient, ctx context.Context) *DatasetStore {
	return &DatasetStore{
		client: client,
		ctx:    ctx,
	}
}

// datasetKey returns the Redis key for dataset info.
func datasetKey(name string) string {
	return fmt.Sprintf("ml:dataset:%s", name)
}

// transferKey returns the Redis key for transfer tracking.
func transferKey(datasetName string) string {
	return fmt.Sprintf("ml:data:transfer:%s", datasetName)
}

// RecordTransferStart records the start of a dataset transfer.
func (s *DatasetStore) RecordTransferStart(ctx context.Context, datasetName, jobName string, sizeBytes int64) error {
	if s.client == nil {
		return nil
	}
	return s.client.HSet(ctx, transferKey(datasetName),
		"status", "transferring",
		"job_name", jobName,
		"size_bytes", sizeBytes,
		"started_at", time.Now().Unix(),
	).Err()
}

// RecordTransferComplete records the successful completion of a dataset transfer.
func (s *DatasetStore) RecordTransferComplete(ctx context.Context, datasetName string, duration time.Duration) error {
	if s.client == nil {
		return nil
	}
	return s.client.HSet(ctx, transferKey(datasetName),
		"status", "completed",
		"completed_at", time.Now().Unix(),
		"duration_seconds", duration.Seconds(),
	).Err()
}

// RecordTransferFailure records a failed dataset transfer.
func (s *DatasetStore) RecordTransferFailure(ctx context.Context, datasetName string, transferErr error) error {
	if s.client == nil {
		return nil
	}
	return s.client.HSet(ctx, transferKey(datasetName),
		"status", "failed",
		"error", transferErr.Error(),
	).Err()
}

// SaveDatasetInfo saves dataset metadata to Redis.
func (s *DatasetStore) SaveDatasetInfo(ctx context.Context, info DatasetInfo) error {
	if s.client == nil {
		return nil
	}
	data, err := json.Marshal(info)
	if err != nil {
		return fmt.Errorf("failed to marshal dataset info: %w", err)
	}
	return s.client.Set(ctx, datasetKey(info.Name), data, 0).Err()
}

// GetDatasetInfo retrieves dataset metadata from Redis.
func (s *DatasetStore) GetDatasetInfo(ctx context.Context, name string) (*DatasetInfo, error) {
	if s.client == nil {
		return nil, nil
	}
	data, err := s.client.Get(ctx, datasetKey(name)).Result()
	if err == redis.Nil {
		return nil, nil
	}
	if err != nil {
		return nil, fmt.Errorf("failed to get dataset info: %w", err)
	}

	var info DatasetInfo
	if err := json.Unmarshal([]byte(data), &info); err != nil {
		return nil, fmt.Errorf("failed to unmarshal dataset info: %w", err)
	}
	return &info, nil
}

// UpdateLastAccess updates the last access time for a dataset.
func (s *DatasetStore) UpdateLastAccess(ctx context.Context, name string) error {
	if s.client == nil {
		return nil
	}
	info, err := s.GetDatasetInfo(ctx, name)
	if err != nil {
		return err
	}
	if info == nil {
		return nil // No record to update
	}

	info.LastAccess = time.Now()
	return s.SaveDatasetInfo(ctx, *info)
}

// DeleteDatasetInfo removes dataset metadata from Redis.
func (s *DatasetStore) DeleteDatasetInfo(ctx context.Context, name string) error {
	if s.client == nil {
		return nil
	}
	return s.client.Del(ctx, datasetKey(name)).Err()
}