package utils

import (
	"crypto/subtle"
	"encoding/base64"
	"errors"
	"fmt"
	"strings"

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

var (
	ErrInvalidHash         = errors.New("the encoded hash is not in the correct format")
	ErrIncompatibleVersion = errors.New("incompatible version of argon2")
)

func Match(password string, email string) (bool, error) {

	user, err := GetUserByEmail(email)
	if err != nil {
		return false, err
	}

	check, err := comparePasswordAndHash(password, user.Password)
	if err != nil {
		return false, err
	}

	return check, nil
}

func comparePasswordAndHash(password, encodedHash string) (match bool, err error) {
	// Extract the parameters, salt and derived key from the encoded password
	// hash.
	p, salt, hash, err := decodeHash(encodedHash)
	if err != nil {
		return false, err
	}

	// Derive the key from the other password using the same parameters.
	otherHash := argon2.IDKey([]byte(password), salt, p.iterations, p.memory, p.parallelism, p.keyLength)

	// Check that the contents of the hashed passwords are identical. Note
	// that we are using the subtle.ConstantTimeCompare() function for this
	// to help prevent timing attacks.
	if subtle.ConstantTimeCompare(hash, otherHash) == 1 {
		return true, nil
	}
	return false, nil
}

func decodeHash(encodedHash string) (p *params, salt, hash []byte, err error) {
	vals := strings.Split(encodedHash, "$")
	if len(vals) != 6 {
		return nil, nil, nil, ErrInvalidHash
	}

	var version int
	_, err = fmt.Sscanf(vals[2], "v=%d", &version)
	if err != nil {
		return nil, nil, nil, err
	}
	if version != argon2.Version {
		return nil, nil, nil, ErrIncompatibleVersion
	}

	p = &params{}
	_, err = fmt.Sscanf(vals[3], "m=%d,t=%d,p=%d", &p.memory, &p.iterations, &p.parallelism)
	if err != nil {
		return nil, nil, nil, err
	}

	salt, err = base64.RawStdEncoding.Strict().DecodeString(vals[4])
	if err != nil {
		return nil, nil, nil, err
	}
	p.saltLength = uint32(len(salt))

	hash, err = base64.RawStdEncoding.Strict().DecodeString(vals[5])
	if err != nil {
		return nil, nil, nil, err
	}
	p.keyLength = uint32(len(hash))

	return p, salt, hash, nil
}