package cryptography

import (
	"bytes"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"io"
)

func randomBytes(n int) ([]byte, error) {
	b := make([]byte, n)
	_, err := io.ReadFull(rand.Reader, b)
	return b, err
}

func normalizeKey(key []byte) ([]byte, error) {
	switch len(key) {
	case 16, 24, 32:
		return key, nil
	default:
		return nil, errors.New("AES key length must be 16, 24, or 32 bytes")
	}
}

func AESGCMEncrypt(plaintext, key []byte) (string, error) {
	key, err := normalizeKey(key)
	if err != nil {
		return "", err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonce, err := randomBytes(gcm.NonceSize())
	if err != nil {
		return "", err
	}

	ciphertext := gcm.Seal(nil, nonce, plaintext, nil)
	out := append(nonce, ciphertext...)

	return base64.RawURLEncoding.EncodeToString(out), nil
}

func AESGCMDecrypt(encoded string, key []byte) ([]byte, error) {
	key, err := normalizeKey(key)
	if err != nil {
		return nil, err
	}

	data, err := base64.RawURLEncoding.DecodeString(encoded)
	if err != nil {
		return nil, err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}

	if len(data) < gcm.NonceSize() {
		return nil, errors.New("ciphertext too short")
	}

	nonce := data[:gcm.NonceSize()]
	ciphertext := data[gcm.NonceSize():]

	return gcm.Open(nil, nonce, ciphertext, nil)
}

func pkcs7Pad(data []byte, blockSize int) []byte {
	padding := blockSize - len(data)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(data, padtext...)
}

func pkcs7Unpad(data []byte) ([]byte, error) {
	length := len(data)
	if length == 0 {
		return nil, errors.New("invalid padding")
	}
	padding := int(data[length-1])
	if padding == 0 || padding > length {
		return nil, errors.New("invalid padding")
	}
	return data[:length-padding], nil
}

func AESCBCEncrypt(plaintext, key []byte) (string, error) {
	key, err := normalizeKey(key)
	if err != nil {
		return "", err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	plaintext = pkcs7Pad(plaintext, block.BlockSize())

	iv, err := randomBytes(block.BlockSize())
	if err != nil {
		return "", err
	}

	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(plaintext, plaintext)

	out := append(iv, plaintext...)
	return base64.RawURLEncoding.EncodeToString(out), nil
}

func AESCBCDecrypt(encoded string, key []byte) ([]byte, error) {
	key, err := normalizeKey(key)
	if err != nil {
		return nil, err
	}

	data, err := base64.RawURLEncoding.DecodeString(encoded)
	if err != nil {
		return nil, err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	if len(data) < block.BlockSize() {
		return nil, errors.New("ciphertext too short")
	}

	iv := data[:block.BlockSize()]
	data = data[block.BlockSize():]

	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(data, data)

	return pkcs7Unpad(data)
}

func AESCFBEncrypt(plaintext, key []byte) (string, error) {
	key, err := normalizeKey(key)
	if err != nil {
		return "", err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	iv, err := randomBytes(block.BlockSize())
	if err != nil {
		return "", err
	}

	stream := cipher.NewCFBEncrypter(block, iv)
	stream.XORKeyStream(plaintext, plaintext)

	out := append(iv, plaintext...)
	return base64.RawURLEncoding.EncodeToString(out), nil
}

func AESCFBDecrypt(encoded string, key []byte) ([]byte, error) {
	key, err := normalizeKey(key)
	if err != nil {
		return nil, err
	}

	data, err := base64.RawURLEncoding.DecodeString(encoded)
	if err != nil {
		return nil, err
	}

	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	if len(data) < block.BlockSize() {
		return nil, errors.New("ciphertext too short")
	}

	iv := data[:block.BlockSize()]
	data = data[block.BlockSize():]

	stream := cipher.NewCFBDecrypter(block, iv)
	stream.XORKeyStream(data, data)

	return data, nil
}