package identity

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

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

const (
	argonMemory      = 64 * 1024
	argonIterations  = 3
	argonParallelism = 2
	argonSaltLength  = 16
	argonKeyLength   = 32
)

func HashPassword(password string) (string, error) {
	if len(password) < 12 {
		return "", errors.New("identity: password must contain at least 12 characters")
	}
	salt := make([]byte, argonSaltLength)
	if _, err := rand.Read(salt); err != nil {
		return "", fmt.Errorf("generating password salt: %w", err)
	}
	hash := argon2.IDKey([]byte(password), salt, argonIterations, argonMemory, argonParallelism, argonKeyLength)
	return fmt.Sprintf("$argon2id$v=19$m=%d,t=%d,p=%d$%s$%s", argonMemory, argonIterations,
		argonParallelism, base64.RawStdEncoding.EncodeToString(salt), base64.RawStdEncoding.EncodeToString(hash)), nil
}

func VerifyPassword(password, encoded string) bool {
	parts := strings.Split(encoded, "$")
	if len(parts) != 6 || parts[1] != "argon2id" || parts[2] != "v=19" {
		return false
	}
	var memory uint32
	var iterations uint32
	var parallelism uint8
	if _, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &iterations, &parallelism); err != nil {
		return false
	}
	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false
	}
	expected, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil || len(expected) == 0 {
		return false
	}
	actual := argon2.IDKey([]byte(password), salt, iterations, memory, parallelism, uint32(len(expected)))
	return subtle.ConstantTimeCompare(actual, expected) == 1
}