package crypto

import (
	"bytes"
	"compress/gzip"
	"io"
)

// CompressEncryptor 压缩加密器
type CompressEncryptor struct {
	baseEncryptor Encryptor
}

func NewCompressEncryptor(encryptor Encryptor) *CompressEncryptor {
	return &CompressEncryptor{baseEncryptor: encryptor}
}

// Encrypt 先压缩后加密
func (c *CompressEncryptor) Encrypt(plaintext []byte) ([]byte, error) {
	// 1. 压缩
	compressed, err := c.compress(plaintext)
	if err != nil {
		return nil, err
	}

	// 2. 加密
	return c.baseEncryptor.Encrypt(compressed)
}

// Decrypt 先解密后解压
func (c *CompressEncryptor) Decrypt(ciphertext []byte) ([]byte, error) {
	// 1. 解密
	compressed, err := c.baseEncryptor.Decrypt(ciphertext)
	if err != nil {
		return nil, err
	}

	// 2. 解压
	return c.decompress(compressed)
}

func (c *CompressEncryptor) Name() string {
	return "GZIP-" + c.baseEncryptor.Name()
}

// compress 使用gzip压缩
func (c *CompressEncryptor) compress(data []byte) ([]byte, error) {
	var buf bytes.Buffer
	writer := gzip.NewWriter(&buf)

	if _, err := writer.Write(data); err != nil {
		return nil, err
	}

	if err := writer.Close(); err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}

// decompress 使用gzip解压
func (c *CompressEncryptor) decompress(data []byte) ([]byte, error) {
	reader, err := gzip.NewReader(bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	defer func() { _ = reader.Close() }()

	return io.ReadAll(reader)
}