package utils

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

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

var (
	Time    uint32 = 3
	Memory  uint32 = 64 * 1024 // 64 MiB (in KiB)
	Threads uint8  = 4
	KeyLen  uint32 = 32
	SaltLen int    = 16
)

// HashPassword hashes a password using Argon2.
func HashPassword(password string) (string, error) {
	salt := make([]byte, SaltLen)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}

	hash := argon2.IDKey([]byte(password), salt, Time, Memory, Threads, KeyLen)

	// Encode salt and hash to base64
	b64Salt := base64.RawStdEncoding.EncodeToString(salt)
	b64Hash := base64.RawStdEncoding.EncodeToString(hash)

	// Format is $argon2id$v=19$m=...,t=...,p=...$salt$hash
	encodedHash := fmt.Sprintf("$argon2id$v=%d$m=%d,t=%d,p=%d$%s$%s",
		argon2.Version, Memory, Time, Threads, b64Salt, b64Hash)

	return encodedHash, nil
}

// ComparePassword verifies a password against an Argon2 hash.
func ComparePassword(password, encodedHash string) (bool, error) {
	parts := strings.Split(encodedHash, "$")
	if len(parts) != 6 {
		return false, fmt.Errorf("invalid hash format")
	}

	var version, m, t, p 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")
	}

	_, 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
	}

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

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

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