package utils

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

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

type Argon2Params struct {
	Memory      uint32
	Iterations  uint32
	Parallelism uint8
	SaltLength  uint32
	KeyLength   uint32
}

// Default secure parameters
var DefaultParams = &Argon2Params{
	Memory:      64 * 1024, // 64 MB
	Iterations:  3,
	Parallelism: 2,
	SaltLength:  16,
	KeyLength:   32,
}

// HashPassword creates a secure Argon2id hash
func HashPassword(password string, p *Argon2Params) (string, error) {
	// Generate salt
	salt := make([]byte, p.SaltLength)
	_, err := rand.Read(salt)
	if err != nil {
		return "", fmt.Errorf("failed to generate salt: %w", err)
	}

	// Calculate hash
	hash := argon2.IDKey([]byte(password), salt, p.Iterations, p.Memory, p.Parallelism, p.KeyLength)

	// Format: $argon2id$v=19$m=65536,t=3,p=2$<salt>$<hash>
	encoded := fmt.Sprintf("$argon2id$v=19$m=%d,t=%d,p=%d$%s$%s",
		p.Memory, p.Iterations, p.Parallelism,
		base64.RawStdEncoding.EncodeToString(salt),
		base64.RawStdEncoding.EncodeToString(hash),
	)

	return encoded, nil
}

// VerifyPassword checks if the 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")
	}

	var memory uint32
	var iterations uint32
	var parallelism uint8
	_, err := fmt.Sscanf(parts[3], "m=%d,t=%d,p=%d", &memory, &iterations, &parallelism)
	if err != nil {
		return false, fmt.Errorf("invalid hash parameters: %w", err)
	}

	// Decode salt and hash
	salt, err := base64.RawStdEncoding.DecodeString(parts[4])
	if err != nil {
		return false, fmt.Errorf("invalid salt encoding: %w", err)
	}
	expectedHash, err := base64.RawStdEncoding.DecodeString(parts[5])
	if err != nil {
		return false, fmt.Errorf("invalid hash encoding: %w", err)
	}

	// Recalculate hash with the same parameters
	hash := argon2.IDKey([]byte(password), salt, iterations, memory, parallelism, uint32(len(expectedHash)))

	// Constant time comparison
	if subtle.ConstantTimeCompare(hash, expectedHash) == 1 {
		return true, nil
	}
	return false, nil
}