package storage

import (
	"context"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"github.com/spf13/afero"
)

// FileStorer implements Storer using the local filesystem.
// It mirrors the S3 path structure for consistency.
type FileStorer struct {
	fs       afero.Fs
	basePath string
}

// NewFileStorer creates a new filesystem storage backend.
// The basePath directory will be created if it doesn't exist.
// Uses the real OS filesystem by default; call SetFilesystem to override for testing.
func NewFileStorer(basePath string) (*FileStorer, error) {
	fs := afero.NewOsFs()
	// Ensure base path exists
	if err := fs.MkdirAll(basePath, 0755); err != nil {
		return nil, fmt.Errorf("creating base path: %w", err)
	}
	return &FileStorer{
		fs:       fs,
		basePath: basePath,
	}, nil
}

// SetFilesystem overrides the filesystem for testing.
func (f *FileStorer) SetFilesystem(fs afero.Fs) {
	f.fs = fs
}

// fullPath returns the full filesystem path for a key.
func (f *FileStorer) fullPath(key string) string {
	return filepath.Join(f.basePath, key)
}

// Put stores data at the specified key.
func (f *FileStorer) Put(ctx context.Context, key string, data io.Reader) error {
	path := f.fullPath(key)

	// Create parent directories
	dir := filepath.Dir(path)
	if err := f.fs.MkdirAll(dir, 0755); err != nil {
		return fmt.Errorf("creating directories: %w", err)
	}

	file, err := f.fs.Create(path)
	if err != nil {
		return fmt.Errorf("creating file: %w", err)
	}
	defer func() { _ = file.Close() }()

	if _, err := io.Copy(file, data); err != nil {
		return fmt.Errorf("writing file: %w", err)
	}

	return nil
}

// PutWithProgress stores data with progress reporting.
func (f *FileStorer) PutWithProgress(ctx context.Context, key string, data io.Reader, size int64, progress ProgressCallback) error {
	path := f.fullPath(key)

	// Create parent directories
	dir := filepath.Dir(path)
	if err := f.fs.MkdirAll(dir, 0755); err != nil {
		return fmt.Errorf("creating directories: %w", err)
	}

	file, err := f.fs.Create(path)
	if err != nil {
		return fmt.Errorf("creating file: %w", err)
	}
	defer func() { _ = file.Close() }()

	// Wrap with progress tracking
	pw := &progressWriter{
		writer:   file,
		callback: progress,
	}

	if _, err := io.Copy(pw, data); err != nil {
		return fmt.Errorf("writing file: %w", err)
	}

	return nil
}

// Get retrieves data from the specified key.
func (f *FileStorer) Get(ctx context.Context, key string) (io.ReadCloser, error) {
	path := f.fullPath(key)
	file, err := f.fs.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, ErrNotFound
		}
		return nil, fmt.Errorf("opening file: %w", err)
	}
	return file, nil
}

// Stat returns metadata about an object without retrieving its contents.
func (f *FileStorer) Stat(ctx context.Context, key string) (*ObjectInfo, error) {
	path := f.fullPath(key)
	info, err := f.fs.Stat(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, ErrNotFound
		}
		return nil, fmt.Errorf("stat file: %w", err)
	}
	return &ObjectInfo{
		Key:  key,
		Size: info.Size(),
	}, nil
}

// Delete removes an object.
func (f *FileStorer) Delete(ctx context.Context, key string) error {
	path := f.fullPath(key)
	err := f.fs.Remove(path)
	if os.IsNotExist(err) {
		return nil // Match S3 behavior: no error if doesn't exist
	}
	if err != nil {
		return fmt.Errorf("removing file: %w", err)
	}
	return nil
}

// List returns all keys with the given prefix.
func (f *FileStorer) List(ctx context.Context, prefix string) ([]string, error) {
	var keys []string
	basePath := f.fullPath(prefix)

	// Check if base path exists
	exists, err := afero.Exists(f.fs, basePath)
	if err != nil {
		return nil, fmt.Errorf("checking path: %w", err)
	}
	if !exists {
		return keys, nil // Empty list for non-existent prefix
	}

	err = afero.Walk(f.fs, basePath, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		// Check context cancellation
		select {
		case <-ctx.Done():
			return ctx.Err()
		default:
		}

		if !info.IsDir() {
			// Convert back to key (relative path from basePath)
			relPath, err := filepath.Rel(f.basePath, path)
			if err != nil {
				return fmt.Errorf("computing relative path: %w", err)
			}
			// Normalize path separators to forward slashes for consistency
			relPath = strings.ReplaceAll(relPath, string(filepath.Separator), "/")
			keys = append(keys, relPath)
		}
		return nil
	})

	if err != nil {
		return nil, fmt.Errorf("walking directory: %w", err)
	}

	return keys, nil
}

// ListStream returns a channel of ObjectInfo for large result sets.
func (f *FileStorer) ListStream(ctx context.Context, prefix string) <-chan ObjectInfo {
	ch := make(chan ObjectInfo)
	go func() {
		defer close(ch)
		basePath := f.fullPath(prefix)

		// Check if base path exists
		exists, err := afero.Exists(f.fs, basePath)
		if err != nil {
			ch <- ObjectInfo{Err: fmt.Errorf("checking path: %w", err)}
			return
		}
		if !exists {
			return // Empty channel for non-existent prefix
		}

		_ = afero.Walk(f.fs, basePath, func(path string, info os.FileInfo, err error) error {
			// Check context cancellation
			select {
			case <-ctx.Done():
				ch <- ObjectInfo{Err: ctx.Err()}
				return ctx.Err()
			default:
			}

			if err != nil {
				ch <- ObjectInfo{Err: err}
				return nil // Continue walking despite errors
			}

			if !info.IsDir() {
				relPath, err := filepath.Rel(f.basePath, path)
				if err != nil {
					ch <- ObjectInfo{Err: fmt.Errorf("computing relative path: %w", err)}
					return nil
				}
				// Normalize path separators
				relPath = strings.ReplaceAll(relPath, string(filepath.Separator), "/")
				ch <- ObjectInfo{
					Key:  relPath,
					Size: info.Size(),
				}
			}
			return nil
		})
	}()
	return ch
}

// Info returns human-readable storage location information.
func (f *FileStorer) Info() StorageInfo {
	return StorageInfo{
		Type:     "file",
		Location: f.basePath,
	}
}

// progressWriter wraps an io.Writer to track write progress.
type progressWriter struct {
	writer   io.Writer
	written  int64
	callback ProgressCallback
}

func (pw *progressWriter) Write(p []byte) (int, error) {
	n, err := pw.writer.Write(p)
	if n > 0 {
		pw.written += int64(n)
		if pw.callback != nil {
			if callbackErr := pw.callback(pw.written); callbackErr != nil {
				return n, callbackErr
			}
		}
	}
	return n, err
}