package utils

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

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

const (
	argon2Time    = 3
	argon2Memory  = 64 * 1024
	argon2Threads = 4
	argon2KeyLen  = 32
	saltLength    = 16
)

func Hash(password string) (string, error) {
	salt := make([]byte, saltLength)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}

	hash := argon2.IDKey([]byte(password), salt, argon2Time, argon2Memory, argon2Threads, argon2KeyLen)

	b64Salt := base64.RawStdEncoding.EncodeToString(salt)
	b64Hash := base64.RawStdEncoding.EncodeToString(hash)

	encodedHash := fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version, argon2Memory, argon2Time, argon2Threads, b64Salt, b64Hash)

	return encodedHash, nil
}

func Verify(password, encodedHash string) (bool, error) {
	parts := strings.Split(encodedHash, "$")
	if len(parts) != 6 {
		return false, fmt.Errorf("invalid hash format")
	}

	if parts[1] != "argon2id" {
		return false, fmt.Errorf("unsupported hash algorithm")
	}

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

	var memory, time uint32
	var threads uint8
	_, err = fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &time, &threads)
	if err != nil {
		return false, err
	}

	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false, err
	}

	hash, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil {
		return false, err
	}

	otherHash := argon2.IDKey([]byte(password), salt, time, memory, threads, uint32(len(hash)))

	if subtle.ConstantTimeCompare(hash, otherHash) == 1 {
		return true, nil
	}

	return false, nil
}