package media

import (
	"context"
	"errors"
	"io"
	"os"
	"path/filepath"
)

// Local stores objects as files under a base directory.
type Local struct {
	dir string
}

// NewLocal creates a Local store rooted at dir, creating it if needed.
func NewLocal(dir string) (*Local, error) {
	if err := os.MkdirAll(dir, 0o750); err != nil {
		return nil, err
	}
	return &Local{dir: dir}, nil
}

func (l *Local) resolve(key string) (string, error) {
	clean := filepath.Clean(filepath.Join(l.dir, key))
	if !hasPrefix(clean, l.dir) {
		return "", errors.New("media: invalid storage key")
	}
	return clean, nil
}

// Save writes the stream to disk atomically under the base directory.
func (l *Local) Save(_ context.Context, key string, r io.Reader) error {
	path, err := l.resolve(key)
	if err != nil {
		return err
	}
	if err := os.MkdirAll(filepath.Dir(path), 0o750); err != nil {
		return err
	}
	tmp, err := os.CreateTemp(filepath.Dir(path), ".upload-*")
	if err != nil {
		return err
	}
	defer os.Remove(tmp.Name())

	if _, err := io.Copy(tmp, r); err != nil {
		tmp.Close()
		return err
	}
	if err := tmp.Close(); err != nil {
		return err
	}
	return os.Rename(tmp.Name(), path)
}

// Open returns a reader for the object or ErrNotFound.
func (l *Local) Open(_ context.Context, key string) (io.ReadCloser, error) {
	path, err := l.resolve(key)
	if err != nil {
		return nil, err
	}
	f, err := os.Open(path)
	if err != nil {
		if os.IsNotExist(err) {
			return nil, ErrNotFound
		}
		return nil, err
	}
	return f, nil
}

// Delete removes the object; missing objects are not an error.
func (l *Local) Delete(_ context.Context, key string) error {
	path, err := l.resolve(key)
	if err != nil {
		return err
	}
	if err := os.Remove(path); err != nil && !os.IsNotExist(err) {
		return err
	}
	return nil
}

func hasPrefix(p, dir string) bool {
	rel, err := filepath.Rel(dir, p)
	if err != nil {
		return false
	}
	return rel != ".." && !startsWithDotDot(rel)
}

func startsWithDotDot(rel string) bool {
	return len(rel) >= 3 && rel[0] == '.' && rel[1] == '.' && (rel[2] == '/' || rel[2] == '\\')
}