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// Package file implements signify file format
package file

import (
	"bufio"
	"encoding"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"strings"
)

const (
	ModeSec   os.FileMode = 0600
	ModePub   os.FileMode = 0644
	ModeSig   os.FileMode = 0644
	untrusted             = "untrusted comment:"
)

var ErrComment = errors.New("expected untrusted comment")

// Block represents a encoded signify key or signature
//
// The encoded form is:
//	untrusted comment: comment
//	base64-encoded key
//	optional message
type Block struct {
	Comment string
	Bytes   []byte
	Message []byte // TODO replace with io.ReadCloser
}

func decodeBlock(r io.Reader) (*Block, error) {
	buf := bufio.NewReader(r)
	comment, err := buf.ReadString('\n')
	if err != nil {
		return nil, err
	}
	if !strings.HasPrefix(comment, untrusted) {
		return nil, ErrComment
	}
	raw, err := buf.ReadString('\n')
	if err != nil {
		return nil, err
	}
	b, err := base64.StdEncoding.DecodeString(raw)
	if err != nil {
		return nil, err
	}
	message, err := ioutil.ReadAll(buf)
	if err != nil {
		return nil, err
	}
	return &Block{
		Comment: strings.TrimSpace(comment[len(untrusted):]),
		Bytes:   b,
		Message: message,
	}, nil
}

func DecodeFile(fname string, u encoding.BinaryUnmarshaler) (string, []byte, error) {
	fd, err := os.Open(fname)
	if err != nil {
		return "", nil, err
	}
	defer fd.Close()
	return Decode(fd, u)
}

func Decode(r io.Reader, u encoding.BinaryUnmarshaler) (string, []byte, error) {
	block, err := decodeBlock(r)
	if err != nil {
		return "", nil, err
	}
	if err := u.UnmarshalBinary(block.Bytes); err != nil {
		return "", nil, err
	}
	return block.Comment, block.Message, nil
}

func encodeBlock(w io.Writer, b *Block) error {
	fmt.Fprintln(w, untrusted, b.Comment)
	fmt.Fprintln(w, base64.StdEncoding.EncodeToString(b.Bytes))
	w.Write(b.Message)
	return nil
}

func EncodeFile(fname string, perm os.FileMode, b *Block) error {
	fd, err := os.OpenFile(fname, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
	if err != nil {
		return err
	}
	defer fd.Close()
	return encodeBlock(fd, b)
}

func Encode(w io.Writer, comment string, u encoding.BinaryMarshaler, msg []byte) error {
	raw, err := u.MarshalBinary()
	if err != nil {
		return err
	}
	b := &Block{
		Comment: comment,
		Bytes:   raw,
		Message: msg,
	}
	return encodeBlock(w, b)
}