/*
 *  Copyright (c) 2017-2018 Samsung Electronics Co., Ltd All Rights Reserved
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License
 */

package dryad

import (
	"crypto/rand"
	"crypto/rsa"
	"os"
	"path"
	"strconv"

	"golang.org/x/crypto/ssh"
)

// sizeRSA is a length of the RSA key.
// It is experimentally chosen value as it is the longest key while still being fast to generate.
const sizeRSA = 1024

// installPublicKey marshals and stores key in a proper location to be read by ssh daemon.
func installPublicKey(key ssh.PublicKey, homedir, uid, gid string) error {
	sshDir := path.Join(homedir, ".ssh")
	err := os.MkdirAll(sshDir, 0755)
	if err != nil {
		return err
	}
	f, err := os.OpenFile(path.Join(sshDir, "authorized_keys"),
		os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
	if err != nil {
		return err
	}
	defer f.Close()
	err = updateOwnership(f, sshDir, uid, gid)
	if err != nil {
		return err
	}
	_, err = f.Write(ssh.MarshalAuthorizedKey(key))
	return err
}

// updateOwnership changes the owner of key and sshDir to uid:gid parsed from uidStr and gidStr.
func updateOwnership(key *os.File, sshDir, uidStr, gidStr string) (err error) {
	uid, err := strconv.Atoi(uidStr)
	if err != nil {
		return
	}
	gid, err := strconv.Atoi(gidStr)
	if err != nil {
		return
	}
	err = os.Chown(sshDir, uid, gid)
	if err != nil {
		return
	}
	return key.Chown(uid, gid)
}

// generateAndInstallKey generates a new RSA key pair, installs the public part,
// changes its owner, and returns the private part.
func generateAndInstallKey(homedir, uid, gid string) (*rsa.PrivateKey, error) {
	key, err := rsa.GenerateKey(rand.Reader, sizeRSA)
	if err != nil {
		return nil, err
	}
	sshPubKey, err := ssh.NewPublicKey(&key.PublicKey)
	if err != nil {
		return nil, err
	}
	err = installPublicKey(sshPubKey, homedir, uid, gid)
	if err != nil {
		return nil, err
	}
	return key, nil
}