package security

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"fmt"
	"strings"
	"unicode"

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

const PasswordCost = 12

type Cipher struct {
	aead    cipher.AEAD
	hmacKey []byte
}

func NewCipher(encryptionKey, hmacKey []byte) (*Cipher, error) {
	if len(encryptionKey) != 32 || len(hmacKey) != 32 {
		return nil, errors.New("encryption and HMAC keys must each be exactly 32 bytes")
	}
	block, err := aes.NewCipher(encryptionKey)
	if err != nil {
		return nil, fmt.Errorf("create AES cipher: %w", err)
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("create AES-GCM: %w", err)
	}
	return &Cipher{aead: aead, hmacKey: append([]byte(nil), hmacKey...)}, nil
}

func (c *Cipher) Encrypt(plaintext string, additionalData []byte) (ciphertext, nonce []byte, err error) {
	nonce = make([]byte, c.aead.NonceSize())
	if _, err := rand.Read(nonce); err != nil {
		return nil, nil, fmt.Errorf("generate nonce: %w", err)
	}
	ciphertext = c.aead.Seal(nil, nonce, []byte(plaintext), additionalData)
	return ciphertext, nonce, nil
}

func (c *Cipher) Decrypt(ciphertext, nonce, additionalData []byte) (string, error) {
	if len(nonce) != c.aead.NonceSize() {
		return "", errors.New("invalid AES-GCM nonce length")
	}
	plaintext, err := c.aead.Open(nil, nonce, ciphertext, additionalData)
	if err != nil {
		return "", errors.New("encrypted field authentication failed")
	}
	return string(plaintext), nil
}

func (c *Cipher) Digest(value string) string {
	mac := hmac.New(sha256.New, c.hmacKey)
	_, _ = mac.Write([]byte(value))
	return hex.EncodeToString(mac.Sum(nil))
}

func NormalizePhone(input string) (string, error) {
	var b strings.Builder
	for i, r := range strings.TrimSpace(input) {
		switch {
		case unicode.IsDigit(r) && r <= unicode.MaxASCII:
			b.WriteRune(r)
		case r == '+' && i == 0:
			b.WriteRune(r)
		case unicode.IsSpace(r) || r == '-' || r == '(' || r == ')':
			continue
		default:
			return "", errors.New("phone may contain only digits, an optional leading +, spaces, dashes and parentheses")
		}
	}
	normalized := b.String()
	digits := strings.TrimPrefix(normalized, "+")
	if len(digits) < 7 || len(digits) > 15 {
		return "", errors.New("phone must contain 7 to 15 digits")
	}
	if strings.HasPrefix(digits, "0") && strings.HasPrefix(normalized, "+") {
		return "", errors.New("international phone cannot start with +0")
	}
	return normalized, nil
}

func GenerateToken() (string, error) {
	raw := make([]byte, 32)
	if _, err := rand.Read(raw); err != nil {
		return "", fmt.Errorf("generate random token: %w", err)
	}
	return base64.RawURLEncoding.EncodeToString(raw), nil
}

func HashToken(token string) string {
	sum := sha256.Sum256([]byte(token))
	return hex.EncodeToString(sum[:])
}

func HashPassword(password string) (string, error) {
	if len(password) < 8 || len(password) > 128 {
		return "", errors.New("password must be 8 to 128 characters")
	}
	encoded, err := bcrypt.GenerateFromPassword([]byte(password), PasswordCost)
	if err != nil {
		return "", fmt.Errorf("hash password: %w", err)
	}
	return string(encoded), nil
}

func VerifyPassword(encoded, password string) bool {
	return bcrypt.CompareHashAndPassword([]byte(encoded), []byte(password)) == nil
}