/*
GoCheese -- Python private package repository and caching proxy
Copyright (C) 2019-2020 Elena Balakhonova <balakhonova_e@riseup.net>

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, version 3 of the License.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

package main

import (
	"bytes"
	"encoding/base64"
	"errors"
	"fmt"
	"strings"

	"golang.org/x/crypto/argon2"
)

type Argon2iAuthData struct {
	version  int
	memory   uint32
	time     uint32
	threads  uint8
	salt     []byte
	password []byte
}

func (ad Argon2iAuthData) Auth(password string) bool {
	hashedPassword := argon2.Key(
		[]byte(password),
		ad.salt,
		ad.time,
		ad.memory,
		ad.threads,
		uint32(len(ad.password)),
	)
	return bytes.Equal(hashedPassword, ad.password)
}

func parseArgon2i(params string) (Auther, error) {
	var time, memory uint32
	var threads uint8
	var version int
	var saltAndPasswordUnitedB64 string
	n, err := fmt.Sscanf(
		params,
		"v=%d$m=%d,t=%d,p=%d$%s",
		&version,
		&memory,
		&time,
		&threads,
		&saltAndPasswordUnitedB64,
	)
	if n != 5 || err != nil {
		return nil, fmt.Errorf("argon2i parameters %q have wrong format", params)
	}
	if version != argon2.Version {
		return nil, errors.New("unsupported argon2i version")
	}
	saltAndPasswordSplittedB64 := strings.Split(saltAndPasswordUnitedB64, "$")
	salt, err := base64.RawStdEncoding.DecodeString(saltAndPasswordSplittedB64[0])
	if err != nil {
		return nil, errors.New("invalid salt format")
	}
	password, err := base64.RawStdEncoding.DecodeString(saltAndPasswordSplittedB64[1])
	if err != nil {
		return nil, errors.New("invalid password format")
	}
	return Argon2iAuthData{
		version:  version,
		time:     time,
		memory:   memory,
		threads:  threads,
		salt:     salt,
		password: password,
	}, nil
}