package s3

import (
	"context"
	"io"
	"sync/atomic"

	"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/feature/s3/manager"
	"github.com/aws/aws-sdk-go-v2/service/s3"
)

// Client wraps the AWS S3 client for vaultik operations.
// It provides a simplified interface for S3 operations with automatic
// prefix handling and connection management. All operations are performed
// within the configured bucket and prefix.
type Client struct {
	s3Client *s3.Client
	bucket   string
	prefix   string
	endpoint string
}

// Config contains S3 client configuration.
// All fields are required except Prefix, which defaults to an empty string.
// The Endpoint field should include the protocol (http:// or https://).
type Config struct {
	Endpoint        string
	Bucket          string
	Prefix          string
	AccessKeyID     string
	SecretAccessKey string
	Region          string
}

// NewClient creates a new S3 client with the provided configuration.
// It establishes a connection to the S3-compatible storage service and
// validates the credentials. The client uses static credentials and
// path-style URLs for compatibility with various S3-compatible services.
func NewClient(ctx context.Context, cfg Config) (*Client, error) {
	// Create AWS config
	awsCfg, err := config.LoadDefaultConfig(ctx,
		config.WithRegion(cfg.Region),
		config.WithCredentialsProvider(credentials.NewStaticCredentialsProvider(
			cfg.AccessKeyID,
			cfg.SecretAccessKey,
			"",
		)),
	)
	if err != nil {
		return nil, err
	}

	// Configure custom endpoint if provided
	s3Opts := func(o *s3.Options) {
		if cfg.Endpoint != "" {
			o.BaseEndpoint = aws.String(cfg.Endpoint)
			o.UsePathStyle = true
		}
	}

	s3Client := s3.NewFromConfig(awsCfg, s3Opts)

	return &Client{
		s3Client: s3Client,
		bucket:   cfg.Bucket,
		prefix:   cfg.Prefix,
		endpoint: cfg.Endpoint,
	}, nil
}

// PutObject uploads an object to S3 with the specified key.
// The key is automatically prefixed with the configured prefix.
// The data parameter should be a reader containing the object data.
// Returns an error if the upload fails.
func (c *Client) PutObject(ctx context.Context, key string, data io.Reader) error {
	fullKey := c.prefix + key
	_, err := c.s3Client.PutObject(ctx, &s3.PutObjectInput{
		Bucket: aws.String(c.bucket),
		Key:    aws.String(fullKey),
		Body:   data,
	})
	return err
}

// ProgressCallback is called during upload progress with bytes uploaded so far.
// The callback should return an error to cancel the upload.
type ProgressCallback func(bytesUploaded int64) error

// PutObjectWithProgress uploads an object to S3 with progress tracking.
// The key is automatically prefixed with the configured prefix.
// The size parameter must be the exact size of the data to upload.
// The progress callback is called periodically with the number of bytes uploaded.
// Returns an error if the upload fails.
func (c *Client) PutObjectWithProgress(ctx context.Context, key string, data io.Reader, size int64, progress ProgressCallback) error {
	fullKey := c.prefix + key

	// Create an uploader with the S3 client
	uploader := manager.NewUploader(c.s3Client, func(u *manager.Uploader) {
		// Set part size to 10MB for better progress granularity
		u.PartSize = 10 * 1024 * 1024
	})

	// Create a progress reader that tracks upload progress
	pr := &progressReader{
		reader:   data,
		size:     size,
		callback: progress,
		read:     0,
	}

	// Upload the file
	_, err := uploader.Upload(ctx, &s3.PutObjectInput{
		Bucket: aws.String(c.bucket),
		Key:    aws.String(fullKey),
		Body:   pr,
	})

	return err
}

// GetObject downloads an object from S3 with the specified key.
// The key is automatically prefixed with the configured prefix.
// Returns a ReadCloser containing the object data. The caller must
// close the returned reader when done to avoid resource leaks.
func (c *Client) GetObject(ctx context.Context, key string) (io.ReadCloser, error) {
	fullKey := c.prefix + key
	result, err := c.s3Client.GetObject(ctx, &s3.GetObjectInput{
		Bucket: aws.String(c.bucket),
		Key:    aws.String(fullKey),
	})
	if err != nil {
		return nil, err
	}
	return result.Body, nil
}

// DeleteObject removes an object from S3 with the specified key.
// The key is automatically prefixed with the configured prefix.
// No error is returned if the object doesn't exist.
func (c *Client) DeleteObject(ctx context.Context, key string) error {
	fullKey := c.prefix + key
	_, err := c.s3Client.DeleteObject(ctx, &s3.DeleteObjectInput{
		Bucket: aws.String(c.bucket),
		Key:    aws.String(fullKey),
	})
	return err
}

// ListObjects lists all objects with the given prefix.
// The prefix is combined with the client's configured prefix.
// Returns a slice of object keys with the base prefix removed.
// This method loads all matching keys into memory, so use
// ListObjectsStream for large result sets.
func (c *Client) ListObjects(ctx context.Context, prefix string) ([]string, error) {
	fullPrefix := c.prefix + prefix

	var keys []string
	paginator := s3.NewListObjectsV2Paginator(c.s3Client, &s3.ListObjectsV2Input{
		Bucket: aws.String(c.bucket),
		Prefix: aws.String(fullPrefix),
	})

	for paginator.HasMorePages() {
		page, err := paginator.NextPage(ctx)
		if err != nil {
			return nil, err
		}

		for _, obj := range page.Contents {
			if obj.Key != nil {
				// Remove the base prefix from the key
				key := *obj.Key
				if len(key) > len(c.prefix) {
					key = key[len(c.prefix):]
				}
				keys = append(keys, key)
			}
		}
	}

	return keys, nil
}

// HeadObject checks if an object exists in S3.
// Returns true if the object exists, false otherwise.
// The key is automatically prefixed with the configured prefix.
// Note: This method returns false for any error, not just "not found".
func (c *Client) HeadObject(ctx context.Context, key string) (bool, error) {
	fullKey := c.prefix + key
	_, err := c.s3Client.HeadObject(ctx, &s3.HeadObjectInput{
		Bucket: aws.String(c.bucket),
		Key:    aws.String(fullKey),
	})
	if err != nil {
		// Check if it's a not found error
		// TODO: Add proper error type checking
		return false, nil
	}
	return true, nil
}

// ObjectInfo contains information about an S3 object.
// It is used by ListObjectsStream to return object metadata
// along with any errors encountered during listing.
type ObjectInfo struct {
	Key  string
	Size int64
	Err  error
}

// ListObjectsStream lists objects with the given prefix and returns a channel.
// This method is preferred for large result sets as it streams results
// instead of loading everything into memory. The channel is closed when
// listing is complete or an error occurs. If an error occurs, it will be
// sent as the last item with the Err field set. The recursive parameter
// is currently unused but reserved for future use.
func (c *Client) ListObjectsStream(ctx context.Context, prefix string, recursive bool) <-chan ObjectInfo {
	ch := make(chan ObjectInfo)

	go func() {
		defer close(ch)

		fullPrefix := c.prefix + prefix

		paginator := s3.NewListObjectsV2Paginator(c.s3Client, &s3.ListObjectsV2Input{
			Bucket: aws.String(c.bucket),
			Prefix: aws.String(fullPrefix),
		})

		for paginator.HasMorePages() {
			page, err := paginator.NextPage(ctx)
			if err != nil {
				ch <- ObjectInfo{Err: err}
				return
			}

			for _, obj := range page.Contents {
				if obj.Key != nil && obj.Size != nil {
					// Remove the base prefix from the key
					key := *obj.Key
					if len(key) > len(c.prefix) {
						key = key[len(c.prefix):]
					}
					ch <- ObjectInfo{
						Key:  key,
						Size: *obj.Size,
					}
				}
			}
		}
	}()

	return ch
}

// StatObject returns information about an object without downloading it.
// The key is automatically prefixed with the configured prefix.
// Returns an ObjectInfo struct with the object's metadata.
// Returns an error if the object doesn't exist or if the operation fails.
func (c *Client) StatObject(ctx context.Context, key string) (*ObjectInfo, error) {
	fullKey := c.prefix + key
	result, err := c.s3Client.HeadObject(ctx, &s3.HeadObjectInput{
		Bucket: aws.String(c.bucket),
		Key:    aws.String(fullKey),
	})
	if err != nil {
		return nil, err
	}

	size := int64(0)
	if result.ContentLength != nil {
		size = *result.ContentLength
	}

	return &ObjectInfo{
		Key:  key,
		Size: size,
	}, nil
}

// RemoveObject deletes an object from S3 (alias for DeleteObject).
// This method exists for API compatibility and simply calls DeleteObject.
func (c *Client) RemoveObject(ctx context.Context, key string) error {
	return c.DeleteObject(ctx, key)
}

// BucketName returns the configured S3 bucket name.
// This is useful for displaying configuration information.
func (c *Client) BucketName() string {
	return c.bucket
}

// Endpoint returns the S3 endpoint URL.
// If no custom endpoint was configured, returns the default AWS S3 endpoint.
// This is useful for displaying configuration information.
func (c *Client) Endpoint() string {
	if c.endpoint == "" {
		return "s3.amazonaws.com"
	}
	return c.endpoint
}

// progressReader wraps an io.Reader to track reading progress
type progressReader struct {
	reader   io.Reader
	size     int64
	read     int64
	callback ProgressCallback
}

// Read implements io.Reader
func (pr *progressReader) Read(p []byte) (int, error) {
	n, err := pr.reader.Read(p)
	if n > 0 {
		atomic.AddInt64(&pr.read, int64(n))
		if pr.callback != nil {
			if callbackErr := pr.callback(atomic.LoadInt64(&pr.read)); callbackErr != nil {
				return n, callbackErr
			}
		}
	}
	return n, err
}