package content

import (
	"archive/tar"
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	digest "github.com/opencontainers/go-digest"
	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
	"github.com/pkg/errors"
)

// ResolveName resolves name from descriptor
func ResolveName(desc ocispec.Descriptor) (string, bool) {
	name, ok := desc.Annotations[ocispec.AnnotationTitle]
	return name, ok
}

// tarDirectory walks the directory specified by path, and tar those files with a new
// path prefix.
func tarDirectory(root, prefix string, w io.Writer) error {
	tw := tar.NewWriter(w)
	defer tw.Close()
	if err := filepath.Walk(root, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}

		// Rename path
		name, err := filepath.Rel(root, path)
		if err != nil {
			return err
		}
		name = filepath.Join(prefix, name)
		name = filepath.ToSlash(name)

		// Generate header
		var link string
		mode := info.Mode()
		if mode&os.ModeSymlink != 0 {
			if link, err = os.Readlink(path); err != nil {
				return err
			}
		}
		header, err := tar.FileInfoHeader(info, link)
		if err != nil {
			return errors.Wrap(err, path)
		}
		header.Name = name
		header.Uid = 0
		header.Gid = 0
		header.Uname = ""
		header.Gname = ""

		// Write file
		if err := tw.WriteHeader(header); err != nil {
			return errors.Wrap(err, "tar")
		}
		if mode.IsRegular() {
			file, err := os.Open(path)
			if err != nil {
				return err
			}
			defer file.Close()
			if _, err := io.Copy(tw, file); err != nil {
				return errors.Wrap(err, path)
			}
		}

		return nil
	}); err != nil {
		return err
	}
	return nil
}

// extractTarDirectory extracts tar file to a directory specified by the `root`
// parameter. The file name prefix is ensured to be the string specified by the
// `prefix` parameter and is trimmed.
func extractTarDirectory(root, prefix string, r io.Reader) error {
	tr := tar.NewReader(r)
	for {
		header, err := tr.Next()
		if err != nil {
			if err == io.EOF {
				return nil
			}
			return err
		}

		// Name check
		name := header.Name
		path, err := filepath.Rel(prefix, name)
		if err != nil {
			return err
		}
		if strings.HasPrefix(path, "../") {
			return fmt.Errorf("%q does not have prefix %q", name, prefix)
		}
		path = filepath.Join(root, path)

		// Create content
		switch header.Typeflag {
		case tar.TypeReg:
			err = writeFile(path, tr, header.FileInfo().Mode())
		case tar.TypeDir:
			err = os.MkdirAll(path, header.FileInfo().Mode())
		case tar.TypeLink:
			err = os.Link(header.Linkname, path)
		case tar.TypeSymlink:
			err = os.Symlink(header.Linkname, path)
		default:
			continue // Non-regular files are skipped
		}
		if err != nil {
			return err
		}

		// Change access time and modification time if possible (error ignored)
		os.Chtimes(path, header.AccessTime, header.ModTime)
	}
}

func writeFile(path string, r io.Reader, perm os.FileMode) error {
	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
	if err != nil {
		return err
	}
	defer file.Close()
	_, err = io.Copy(file, r)
	return err
}

func extractTarGzip(root, prefix, filename, checksum string) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()
	zr, err := gzip.NewReader(file)
	if err != nil {
		return err
	}
	defer zr.Close()
	var r io.Reader = zr
	var verifier digest.Verifier
	if checksum != "" {
		if digest, err := digest.Parse(checksum); err == nil {
			verifier = digest.Verifier()
			r = io.TeeReader(r, verifier)
		}
	}
	if err := extractTarDirectory(root, prefix, r); err != nil {
		return err
	}
	if verifier != nil && !verifier.Verified() {
		return errors.New("content digest mismatch")
	}
	return nil
}
