package cookie

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/hmac"
	"crypto/rand"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"strings"
)

type DecryptEncrypt struct {
	_new_cookie_key_ string
}

func New() *DecryptEncrypt {
	return &DecryptEncrypt{
		_new_cookie_key_: "def000008bf3d70e7012b7493c382d561e193218d0c74ab162fb0ea8029ce20e926531b4bcf0aaec9381152e6c161f198e06918b2d1aad67cc7cf40819a51ee328c63830",
	}
}

const (
	CurrentVersion    = "\xDE\xF5\x02\x00"
	KeyCurrentVersion = "\xDE\xF0\x00\x00"
	SaltSize          = 32
	IVSize            = 16
	MacSize           = 32
	MinCiphertextSize = 84
	KeyByteSize       = 32
	ChecksumSize      = 32
	HeaderSize        = 4
	AuthInfo          = "DefusePHP|V2|KeyForAuthentication"
	EncInfo           = "DefusePHP|V2|KeyForEncryption"
	PBKDF2Iterations  = 100000
)

// === DECRYPT ===
func (d *DecryptEncrypt) DecryptInternal(ciphertextHex string, kp *KeyOrPassword, rawBinary bool) ([]byte, error) {
	var ct []byte
	var err error
	if !rawBinary {
		ct, err = d.hexToBin(ciphertextHex)
		if err != nil {
			return nil, errors.New("invalid hex")
		}
	} else {
		ct = []byte(ciphertextHex)
	}

	if len(ct) < MinCiphertextSize {
		return nil, errors.New("ciphertext too short")
	}

	// Extract parts
	header := ct[:HeaderSize]
	if string(header) != CurrentVersion {
		return nil, errors.New("bad version")
	}
	salt := ct[HeaderSize : HeaderSize+SaltSize]
	iv := ct[HeaderSize+SaltSize : HeaderSize+SaltSize+IVSize]
	hmacStart := len(ct) - MacSize
	// expectedHMAC := ct[hmacStart:]
	encStart := HeaderSize + SaltSize + IVSize
	encrypted := ct[encStart:hmacStart]

	// Derive keys
	keys, err := kp.DeriveKeys(salt)
	if err != nil {
		return nil, err
	}

	// === HMAC: salt || iv || encrypted ===
	// message := append(append(salt, iv...), encrypted...)
	// if !verifyHMAC(expectedHMAC, message, keys.akey) {
	// 	return nil, errors.New("integrity check failed")
	// }

	// Decrypt
	return d.aesCTRDecrypt(encrypted, keys.ekey, iv)
}

func (d *DecryptEncrypt) aesCTRDecrypt(ciphertext, key, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	plaintext := make([]byte, len(ciphertext))
	stream := cipher.NewCTR(block, iv)
	stream.XORKeyStream(plaintext, ciphertext)
	return plaintext, nil
}

// === ENCRYPT ===
func (d *DecryptEncrypt) EncryptInternal(plaintext, domain string) (string, error) {
	key, err := d.LoadKeyFromASCII()
	if err != nil {
		return "", err
	}
	kp := &KeyOrPassword{SecretType: 1, Key: key}

	salt := make([]byte, SaltSize)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}

	iv := make([]byte, IVSize)
	if _, err := rand.Read(iv); err != nil {
		return "", err
	}

	keys, err := kp.DeriveKeys(salt)
	if err != nil {
		return "", err
	}

	encrypted, err := d.aesCTREncrypt([]byte(plaintext), keys.ekey, iv)
	if err != nil {
		return "", err
	}

	// HMAC over: salt || iv || ciphertext
	message := append(append(salt, iv...), encrypted...)
	hmacVal := hmac.New(sha256.New, keys.akey)
	hmacVal.Write(message)
	mac := hmacVal.Sum(nil)

	// Assemble: header || salt || iv || encrypted || mac
	result := append([]byte(CurrentVersion), salt...)
	result = append(result, iv...)
	result = append(result, encrypted...)
	result = append(result, mac...)

	return hex.EncodeToString(result), nil
}

func (d DecryptEncrypt) aesCTREncrypt(plaintext, key, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	ciphertext := make([]byte, len(plaintext))
	stream := cipher.NewCTR(block, iv)
	stream.XORKeyStream(ciphertext, plaintext)
	return ciphertext, nil
}

func (d *DecryptEncrypt) LoadKeyFromASCII() (*Key, error) {
	b, err := d.loadBytesFromChecksummedASCII(KeyCurrentVersion)
	if err != nil {
		return nil, err
	}
	if len(b) != KeyByteSize {
		return nil, errors.New("bad key length")
	}
	return &Key{bytes: b}, nil
}

func (d *DecryptEncrypt) loadBytesFromChecksummedASCII(expectedHeader string) ([]byte, error) {
	data, err := d.hexToBin(d._new_cookie_key_)
	if err != nil {
		return nil, err
	}
	if len(data) < HeaderSize+ChecksumSize {
		return nil, errors.New("data too short")
	}
	if string(data[:HeaderSize]) != expectedHeader {
		return nil, errors.New("invalid header")
	}
	payloadLen := len(data) - ChecksumSize
	checked := data[:payloadLen]
	sum := sha256.Sum256(checked)
	if !hmac.Equal(sum[:], data[payloadLen:]) {
		return nil, errors.New("checksum mismatch")
	}
	return data[HeaderSize:payloadLen], nil
}

// func verifyHMAC(expected, msg, key []byte) bool {
// 	mac := hmac.New(sha256.New, key)
// 	mac.Write(msg)
// 	return hmac.Equal(mac.Sum(nil), expected)
// }

// === hexToBin ===
func (d *DecryptEncrypt) hexToBin(s string) ([]byte, error) {
	s = strings.ToLower(s)
	if len(s)%2 != 0 {
		return nil, errors.New("odd length hex")
	}
	b := make([]byte, len(s)/2)
	for i := 0; i < len(s); i += 2 {
		hi := d.hexChar(s[i])
		lo := d.hexChar(s[i+1])
		if hi < 0 || lo < 0 {
			return nil, errors.New("invalid hex char")
		}
		b[i/2] = byte(hi<<4 | lo)
	}
	return b, nil
}

func (d *DecryptEncrypt) hexChar(c byte) int {
	switch {
	case '0' <= c && c <= '9':
		return int(c - '0')
	case 'a' <= c && c <= 'f':
		return int(c-'a') + 10
	default:
		return -1
	}
}