package auth

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

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

const (
	argonTime    = 1
	argonMemory  = 64 * 1024
	argonThreads = 4
	argonKeyLen  = 32
	argonSaltLen = 16
)

func HashPassword(password string) (string, error) {
	if len(password) < 8 {
		return "", ErrPasswordTooShort
	}
	salt := make([]byte, argonSaltLen)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	hash := argon2.IDKey([]byte(password), salt, argonTime, argonMemory, argonThreads, argonKeyLen)
	b64Salt := base64.RawStdEncoding.EncodeToString(salt)
	b64Hash := base64.RawStdEncoding.EncodeToString(hash)
	return fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version, argonMemory, argonTime, argonThreads, b64Salt, b64Hash), nil
}

func VerifyPassword(encoded, password string) (bool, error) {
	parts := strings.Split(encoded, "$")
	if len(parts) != 6 || parts[1] != "argon2id" {
		return false, errors.New("invalid password hash format")
	}
	var version int
	if _, err := fmt.Sscanf(parts[2], "v=%d", &version); err != nil {
		return false, err
	}
	var memory, timeCost uint32
	var threads uint8
	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &timeCost, &threads); err != nil {
		return false, err
	}
	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false, err
	}
	want, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil {
		return false, err
	}
	got := argon2.IDKey([]byte(password), salt, timeCost, memory, threads, uint32(len(want)))
	return subtle.ConstantTimeCompare(want, got) == 1, nil
}