package password

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

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

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

// HashPassword creates an argon2id hash of the password
func HashPassword(password string) string {
	salt := make([]byte, 16)
	rand.Read(salt)

	hash := argon2.IDKey([]byte(password), salt, argonTime, argonMemory, argonThreads, argonKeyLen)

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

	encoded := fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version, argonMemory, argonTime, argonThreads, b64Salt, b64Hash)

	return encoded
}

// VerifyPassword checks if a password matches the hash
func VerifyPassword(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("invalid hash variant")
	}

	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 argon2 version")
	}

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

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

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

	hash := argon2.IDKey([]byte(password), salt, t, m, uint8(p), uint32(len(expectedHash)))

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

	return false, nil
}