// Copyright 2014 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.

package fs

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
)

// Copy recursively copies the file, directory or symbolic link at src
// to dst. The destination must not exist. Symbolic links are not
// followed.
//
// If the copy fails half way through, the destination might be left
// partially written.
func Copy(src, dst string) error {
	srcInfo, srcErr := os.Lstat(src)
	if srcErr != nil {
		return srcErr
	}
	_, dstErr := os.Lstat(dst)
	if dstErr == nil {
		// TODO(rog) add a flag to permit overwriting?
		return fmt.Errorf("will not overwrite %q", dst)
	}
	if !os.IsNotExist(dstErr) {
		return dstErr
	}
	switch mode := srcInfo.Mode(); mode & os.ModeType {
	case os.ModeSymlink:
		return copySymLink(src, dst)
	case os.ModeDir:
		return copyDir(src, dst, mode)
	case 0:
		return copyFile(src, dst, mode)
	default:
		return fmt.Errorf("cannot copy file with mode %v", mode)
	}
}

func copySymLink(src, dst string) error {
	target, err := os.Readlink(src)
	if err != nil {
		return err
	}
	return os.Symlink(target, dst)
}

func copyFile(src, dst string, mode os.FileMode) error {
	srcf, err := os.Open(src)
	if err != nil {
		return err
	}
	defer srcf.Close()
	dstf, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, mode.Perm())
	if err != nil {
		return err
	}
	defer dstf.Close()
	// Make the actual permissions match the source permissions
	// even in the presence of umask.
	if err := os.Chmod(dstf.Name(), mode.Perm()); err != nil {
		return err
	}
	if _, err := io.Copy(dstf, srcf); err != nil {
		return fmt.Errorf("cannot copy %q to %q: %v", src, dst, err)
	}
	return nil
}

func copyDir(src, dst string, mode os.FileMode) error {
	srcf, err := os.Open(src)
	if err != nil {
		return err
	}
	defer srcf.Close()
	if mode&0500 == 0 {
		// The source directory doesn't have write permission,
		// so give the new directory write permission anyway
		// so that we have permission to create its contents.
		// We'll make the permissions match at the end.
		mode |= 0500
	}
	if err := os.Mkdir(dst, mode.Perm()); err != nil {
		return err
	}
	for {
		names, err := srcf.Readdirnames(100)
		for _, name := range names {
			if err := Copy(filepath.Join(src, name), filepath.Join(dst, name)); err != nil {
				return err
			}
		}
		if err == io.EOF {
			break
		}
		if err != nil {
			return fmt.Errorf("error reading directory %q: %v", src, err)
		}
	}
	if err := os.Chmod(dst, mode.Perm()); err != nil {
		return err
	}
	return nil
}