// Package auth : hachage de mots de passe (argon2id) et JWT.
package auth

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

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

// Paramètres argon2id (OWASP Password Storage Cheat Sheet).
const (
	argonTime    = 1
	argonMemory  = 64 * 1024 // 64 MiB
	argonThreads = 4
	argonKeyLen  = 32
	argonSaltLen = 16
)

var ErrInvalidHash = errors.New("format de hash invalide")

// HashPassword produit un hash argon2id encodé (format PHC).
func HashPassword(password string) (string, error) {
	salt := make([]byte, argonSaltLen)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	key := argon2.IDKey([]byte(password), salt, argonTime, argonMemory, argonThreads, argonKeyLen)
	return fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version, argonMemory, argonTime, argonThreads,
		base64.RawStdEncoding.EncodeToString(salt),
		base64.RawStdEncoding.EncodeToString(key),
	), nil
}

// VerifyPassword compare un mot de passe à un hash encodé, en temps constant.
func VerifyPassword(password, encoded string) (bool, error) {
	parts := strings.Split(encoded, "$")
	if len(parts) != 6 || parts[1] != "argon2id" {
		return false, ErrInvalidHash
	}
	var memory, time uint32
	var threads uint8
	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &time, &threads); err != nil {
		return false, ErrInvalidHash
	}
	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false, ErrInvalidHash
	}
	want, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil {
		return false, ErrInvalidHash
	}
	got := argon2.IDKey([]byte(password), salt, time, memory, threads, uint32(len(want)))
	return subtle.ConstantTimeCompare(got, want) == 1, nil
}