package shadowsocks_2022

import (
	"crypto/aes"
	"crypto/cipher"
	"errors"
	"strings"

	"golang.org/x/crypto/chacha20poly1305"
)

type CipherMethod struct {
	Name          string
	KeySaltLength int
	IsChaCha      bool
}

var methods = map[string]*CipherMethod{
	MethodAES128GCM:        {Name: MethodAES128GCM, KeySaltLength: 16, IsChaCha: false},
	MethodAES256GCM:        {Name: MethodAES256GCM, KeySaltLength: 32, IsChaCha: false},
	MethodChaCha20Poly1305: {Name: MethodChaCha20Poly1305, KeySaltLength: 32, IsChaCha: true},
}

func GetCipherMethod(name string) (*CipherMethod, error) {
	name = strings.ToLower(name)
	if m, ok := methods[name]; ok {
		return m, nil
	}
	return nil, errors.New("unknown shadowsocks 2022 method")
}

// NewAEAD creates standard stream AEAD cipher instance (AES-GCM or ChaCha20-Poly1305)
func (m *CipherMethod) NewAEAD(key []byte) (cipher.AEAD, error) {
	if m.IsChaCha {
		return chacha20poly1305.New(key)
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	return cipher.NewGCM(block)
}

// NewBlock creates standard 16-byte block cipher for AES header encryption/decryption
func (m *CipherMethod) NewBlock(key []byte) (cipher.Block, error) {
	return aes.NewCipher(key)
}

// NewUDPCipher creates AEAD cipher for UDP packets (XChaCha20-Poly1305 with 24-byte nonce)
func (m *CipherMethod) NewUDPCipher(key []byte) (cipher.AEAD, error) {
	if m.IsChaCha {
		return chacha20poly1305.NewX(key)
	}
	return nil, errors.New("shadowsocks-2022: udp separate AEAD cipher only available for chacha20 method")
}