package store

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

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

// argon2id with sane defaults
const (
	argonTime    = 1
	argonMemory  = 64 * 1024
	argonThreads = 4
	argonKeyLen  = 32
	argonSaltLen = 16
)

// Argon2IDHash hashes a password with argon2id.
func Argon2IDHash(pw string) (string, error) {
	salt := make([]byte, argonSaltLen)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	key := argon2.IDKey([]byte(pw), salt, argonTime, argonMemory, argonThreads, argonKeyLen)
	return fmt.Sprintf("$argon2id$v=19$m=%d,t=%d,p=%d$%s$%s",
		argonMemory, argonTime, argonThreads,
		base64.RawStdEncoding.EncodeToString(salt), base64.RawStdEncoding.EncodeToString(key)), nil
}

func CheckPassword(hash, pw string) bool {
	parts := strings.Split(hash, "$")
	if len(parts) != 6 || parts[1] != "argon2id" {
		return false
	}
	var m, t uint32
	var p uint8
	fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &m, &t, &p)
	salt, err1 := base64.RawStdEncoding.DecodeString(parts[4])
	want, err2 := base64.RawStdEncoding.DecodeString(parts[5])
	if err1 != nil || err2 != nil {
		return false
	}
	got := argon2.IDKey([]byte(pw), salt, t, m, p, uint32(len(want)))
	return subtle.ConstantTimeCompare(got, want) == 1
}

// cryptoRead is used by genSlug
func cryptoRead(b []byte) (int, error) { return rand.Read(b) }