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package main

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

type File struct {
	Comment string
	B64     []byte
	Body    []byte
}

const (
	commentHdr = "untrusted comment:"
	verifyWith = "verify with"
	pubKey     = "%s public key"
	secKey     = "%s secret key"
	sigFrom    = "signature from %s"
)

func checkComment(comment string) error {
	// compatibility with original version
	if len(comment) > 1024 {
		return errors.New("comment line to long")
	}
	if !strings.HasPrefix(comment, commentHdr) {
		return errors.New("expected untrusted comment")
	}
	return nil
}

func (f *File) ReadFrom(r io.Reader) error {
	buf := bufio.NewReader(r)

	comment, err := buf.ReadString('\n')
	if err != nil {
		return err
	}
	if err := checkComment(comment); err != nil {
		return err
	}
	f.Comment = strings.TrimSpace(comment[len(commentHdr):])

	b64, err := buf.ReadBytes('\n')
	if err != nil {
		return err
	}
	f.B64 = bytes.TrimSpace(b64)

	f.Body, err = ioutil.ReadAll(buf)
	if err != nil {
		return err
	}

	return nil
}

func Parse(b []byte) (*File, error) {
	r := bytes.NewReader(b)
	f := new(File)
	return f, f.ReadFrom(r)
}

func ParseFile(fname string) (*File, error) {
	fd, err := os.Open(fname)
	if err != nil {
		return nil, err
	}
	defer fd.Close()
	f := new(File)
	return f, f.ReadFrom(fd)
}

func (f File) Bytes() ([]byte, error) {
	buf := new(bytes.Buffer)
	err := f.WriteTo(buf)
	if err != nil {
		return nil, err
	}
	return buf.Bytes(), nil
}

func (f File) WriteTo(w io.Writer) error {
	fmt.Fprintln(w, commentHdr, f.Comment)
	fmt.Fprintln(w, string(f.B64))
	if f.Body != nil {
		w.Write(f.Body)
	}
	return nil
}

const (
	SecMode os.FileMode = 0600
	PubMode os.FileMode = 0644
)

func (f File) WriteFile(fname string, perm os.FileMode) error {
	fd, err := os.OpenFile(fname, os.O_WRONLY|os.O_CREATE, perm)
	if err != nil {
		return err
	}
	defer fd.Close()
	return f.WriteTo(fd)
}