package storage

import (
	"bytes"
	"context"
	"crypto/rand"
	"errors"
	"fmt"
	"io"
	"strings"
	"time"

	"github.com/rclone/rclone/fs"
	"github.com/rclone/rclone/fs/config/configfile"
	"github.com/rclone/rclone/fs/operations"

	// Import all rclone backends
	_ "github.com/rclone/rclone/backend/all"
)

// ErrRemoteNotFound is returned when an rclone remote is not configured.
var ErrRemoteNotFound = errors.New("rclone remote not found in config")

// RcloneStorer implements Storer using rclone's filesystem abstraction.
// This allows vaultik to use any of rclone's 70+ supported storage providers.
type RcloneStorer struct {
	fsys   fs.Fs  // rclone filesystem
	remote string // remote name (for Info())
	path   string // path within remote (for Info())
}

// NewRcloneStorer creates a new rclone storage backend.
// The remote parameter is the rclone remote name (as configured via `rclone config`).
// The path parameter is the path within the remote.
func NewRcloneStorer(ctx context.Context, remote, path string) (*RcloneStorer, error) {
	// Install the default config file handler
	configfile.Install()

	// Build the rclone path string (e.g., "myremote:path/to/backups")
	rclonePath := remote + ":"
	if path != "" {
		rclonePath += path
	}

	// Create the rclone filesystem
	fsys, err := fs.NewFs(ctx, rclonePath)
	if err != nil {
		// Check for remote not found error
		if strings.Contains(err.Error(), "didn't find section in config file") ||
			strings.Contains(err.Error(), "failed to find remote") {
			return nil, fmt.Errorf("%w: %s", ErrRemoteNotFound, remote)
		}

		return nil, fmt.Errorf("creating rclone filesystem: %w", err)
	}

	return &RcloneStorer{
		fsys:   fsys,
		remote: remote,
		path:   path,
	}, nil
}

// Put stores data at the specified key.
func (r *RcloneStorer) Put(ctx context.Context, key string, data io.Reader) error {
	// Read all data into memory to get size (required by rclone)
	buf, err := io.ReadAll(data)
	if err != nil {
		return fmt.Errorf("reading data: %w", err)
	}

	return r.upload(ctx, key, bytes.NewReader(buf))
}

// PutWithProgress stores data with progress reporting.
func (r *RcloneStorer) PutWithProgress(
	ctx context.Context, key string, data io.Reader,
	_ int64, progress ProgressCallback,
) error {
	// Wrap reader with progress tracking
	pr := &progressReader{
		reader:   data,
		callback: progress,
	}

	return r.upload(ctx, key, pr)
}

// Get retrieves data from the specified key.
func (r *RcloneStorer) Get(ctx context.Context, key string) (io.ReadCloser, error) {
	// Get the object
	obj, err := r.fsys.NewObject(ctx, key)
	if err != nil {
		if errors.Is(err, fs.ErrorObjectNotFound) {
			return nil, ErrNotFound
		}

		if errors.Is(err, fs.ErrorDirNotFound) {
			return nil, ErrNotFound
		}

		return nil, fmt.Errorf("getting object: %w", err)
	}

	// Open the object for reading
	reader, err := obj.Open(ctx)
	if err != nil {
		return nil, fmt.Errorf("opening object: %w", err)
	}

	return reader, nil
}

// Stat returns metadata about an object without retrieving its contents.
func (r *RcloneStorer) Stat(ctx context.Context, key string) (*ObjectInfo, error) {
	obj, err := r.fsys.NewObject(ctx, key)
	if err != nil {
		if errors.Is(err, fs.ErrorObjectNotFound) {
			return nil, ErrNotFound
		}

		if errors.Is(err, fs.ErrorDirNotFound) {
			return nil, ErrNotFound
		}

		return nil, fmt.Errorf("getting object: %w", err)
	}

	return &ObjectInfo{
		Key:  key,
		Size: obj.Size(),
	}, nil
}

// Delete removes an object.
func (r *RcloneStorer) Delete(ctx context.Context, key string) error {
	obj, err := r.fsys.NewObject(ctx, key)
	if err != nil {
		if errors.Is(err, fs.ErrorObjectNotFound) {
			return nil // Match S3 behavior: no error if doesn't exist
		}

		if errors.Is(err, fs.ErrorDirNotFound) {
			return nil
		}

		return fmt.Errorf("getting object: %w", err)
	}

	err = obj.Remove(ctx)
	if err != nil {
		return fmt.Errorf("removing object: %w", err)
	}

	return nil
}

// List returns all keys with the given prefix.
func (r *RcloneStorer) List(ctx context.Context, prefix string) ([]string, error) {
	var keys []string

	err := operations.ListFn(ctx, r.fsys, func(obj fs.Object) {
		key := obj.Remote()
		if strings.HasSuffix(key, tempSuffix) {
			return
		}

		if prefix == "" || strings.HasPrefix(key, prefix) {
			keys = append(keys, key)
		}
	})
	if err != nil {
		return nil, fmt.Errorf("listing objects: %w", err)
	}

	return keys, nil
}

// ListStream returns a channel of ObjectInfo for large result sets.
func (r *RcloneStorer) ListStream(
	ctx context.Context, prefix string,
) <-chan ObjectInfo {
	ch := make(chan ObjectInfo)

	go func() {
		defer close(ch)

		err := operations.ListFn(ctx, r.fsys, func(obj fs.Object) {
			// Check context cancellation
			select {
			case <-ctx.Done():
				return
			default:
			}

			key := obj.Remote()
			if strings.HasSuffix(key, tempSuffix) {
				return
			}

			if prefix == "" || strings.HasPrefix(key, prefix) {
				ch <- ObjectInfo{
					Key:  key,
					Size: obj.Size(),
				}
			}
		})
		if err != nil {
			ch <- ObjectInfo{Err: fmt.Errorf("listing objects: %w", err)}
		}
	}()

	return ch
}

// Info returns human-readable storage location information.
func (r *RcloneStorer) Info() Info {
	location := r.remote
	if r.path != "" {
		location += ":" + r.path
	}

	return Info{
		Type:     schemeRclone,
		Location: location,
	}
}

// upload writes data to key. On a remote where rclone says a file can be
// seen while it is still being written (its PartialUploads feature: local,
// sftp, ftp, smb and others), it writes under a temporary name ending in
// tempSuffix and moves the object onto key once it is complete, as
// rclone's own copy does, so a killed upload cannot leave a truncated
// object at key. List and ListStream skip a temporary object left behind.
func (r *RcloneStorer) upload(ctx context.Context, key string, data io.Reader) error {
	features := r.fsys.Features()
	if !features.PartialUploads || features.Move == nil {
		_, err := operations.Rcat(ctx, r.fsys, key, io.NopCloser(data), time.Now(), nil)
		if err != nil {
			return fmt.Errorf("uploading object: %w", err)
		}

		return nil
	}

	tempKey := key + "-" + rand.Text() + tempSuffix

	obj, err := operations.Rcat(ctx, r.fsys, tempKey, io.NopCloser(data), time.Now(), nil)
	if err != nil {
		// Rcat returns the object it wrote when the written data fails its check.
		if obj != nil {
			_ = obj.Remove(ctx)
		}

		return fmt.Errorf("uploading object: %w", err)
	}

	_, err = features.Move(ctx, obj, key)
	if err != nil {
		_ = obj.Remove(ctx)

		return fmt.Errorf("moving object into place: %w", err)
	}

	return nil
}

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

func (pr *progressReader) Read(p []byte) (int, error) {
	n, err := pr.reader.Read(p)
	if n > 0 {
		pr.read += int64(n)
		if pr.callback != nil {
			callbackErr := pr.callback(pr.read)
			if callbackErr != nil {
				return n, callbackErr
			}
		}
	}

	return n, err
}