package storage

import (
	"bytes"
	"context"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"fmt"
	"io"

	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/config"
	"github.com/aws/aws-sdk-go-v2/credentials"
	"github.com/aws/aws-sdk-go-v2/service/s3"
	orchardconfig "github.com/bsf/orchard/internal/config"
)

// S3Storage implements content-addressable storage using S3
type S3Storage struct {
	client *s3.Client
	bucket string
}

// NewS3Storage creates a new S3 storage backend
func NewS3Storage(cfg *orchardconfig.S3Config) (*S3Storage, error) {
	customResolver := aws.EndpointResolverWithOptionsFunc(func(service, region string, options ...interface{}) (aws.Endpoint, error) {
		if cfg.Endpoint != "" {
			return aws.Endpoint{
				URL:               cfg.Endpoint,
				HostnameImmutable: true,
			}, nil
		}
		return aws.Endpoint{}, &aws.EndpointNotFoundError{}
	})

	awsCfg, err := config.LoadDefaultConfig(context.Background(),
		config.WithRegion(cfg.Region),
		config.WithEndpointResolverWithOptions(customResolver),
		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(
			cfg.AccessKeyID,
			cfg.SecretAccessKey,
			"",
		)),
	)
	if err != nil {
		return nil, fmt.Errorf("failed to load AWS config: %w", err)
	}

	client := s3.NewFromConfig(awsCfg, func(o *s3.Options) {
		o.UsePathStyle = cfg.UsePathStyle
	})

	return &S3Storage{
		client: client,
		bucket: cfg.Bucket,
	}, nil
}

// hashToKey converts a SHA256 hash to an S3 object key
// Uses directory structure: ab/cd/abcdef123...
func hashToKey(hash string) string {
	if len(hash) < 4 {
		return hash
	}
	return fmt.Sprintf("%s/%s/%s", hash[:2], hash[2:4], hash)
}

// Store uploads content to S3 and returns the SHA256 hash
func (s *S3Storage) Store(ctx context.Context, reader io.Reader) (string, int64, error) {
	// Read all content into memory to compute hash and enable seeking
	data, err := io.ReadAll(reader)
	if err != nil {
		return "", 0, fmt.Errorf("failed to read content: %w", err)
	}

	size := int64(len(data))

	// Compute SHA256 hash
	hasher := sha256.New()
	hasher.Write(data)
	hash := hex.EncodeToString(hasher.Sum(nil))
	finalKey := hashToKey(hash)

	// Check if object already exists (deduplication)
	_, err = s.client.HeadObject(ctx, &s3.HeadObjectInput{
		Bucket: aws.String(s.bucket),
		Key:    aws.String(finalKey),
	})
	if err == nil {
		// Object already exists, return existing hash (deduplication)
		return hash, size, nil
	}

	// Upload to final location
	_, err = s.client.PutObject(ctx, &s3.PutObjectInput{
		Bucket:        aws.String(s.bucket),
		Key:           aws.String(finalKey),
		Body:          bytes.NewReader(data),
		ContentLength: aws.Int64(size),
	})
	if err != nil {
		return "", 0, fmt.Errorf("failed to upload to S3: %w", err)
	}

	return hash, size, nil
}

// Retrieve downloads content by SHA256 hash
func (s *S3Storage) Retrieve(ctx context.Context, hash string) (io.ReadCloser, error) {
	key := hashToKey(hash)

	result, err := s.client.GetObject(ctx, &s3.GetObjectInput{
		Bucket: aws.String(s.bucket),
		Key:    aws.String(key),
	})
	if err != nil {
		return nil, fmt.Errorf("failed to retrieve object: %w", err)
	}

	return result.Body, nil
}

// Exists checks if a fruit exists by hash
func (s *S3Storage) Exists(ctx context.Context, hash string) (bool, error) {
	key := hashToKey(hash)

	_, err := s.client.HeadObject(ctx, &s3.HeadObjectInput{
		Bucket: aws.String(s.bucket),
		Key:    aws.String(key),
	})
	if err != nil {
		return false, nil
	}
	return true, nil
}

// GetSize returns the size of a stored object
func (s *S3Storage) GetSize(ctx context.Context, hash string) (int64, error) {
	key := hashToKey(hash)

	result, err := s.client.HeadObject(ctx, &s3.HeadObjectInput{
		Bucket: aws.String(s.bucket),
		Key:    aws.String(key),
	})
	if err != nil {
		return 0, fmt.Errorf("failed to get object metadata: %w", err)
	}

	return *result.ContentLength, nil
}

// generateTempID creates a unique temporary ID
func generateTempID() string {
	b := make([]byte, 16)
	rand.Read(b)
	return hex.EncodeToString(b)
}