package weixin_ilink

import (
	"bytes"
	"crypto/aes"
	"errors"
	"strconv"
	"testing"
)

func TestAESECB_RoundTrip_AllBlockBoundaries(t *testing.T) {
	t.Parallel()
	key := bytes.Repeat([]byte{0x42}, aes.BlockSize)
	// 覆盖长度 0 到刚过两个分组的范围（填充边界情况）。
	for n := 0; n <= 2*aes.BlockSize+5; n++ {
		n := n
		t.Run("len="+strconv.Itoa(n), func(t *testing.T) {
			t.Parallel()
			pt := bytes.Repeat([]byte{0xAB}, n)
			ct, err := aesECBEncrypt(key, pt)
			if err != nil {
				t.Fatalf("aesECBEncrypt: %v", err)
			}
			got, err := aesECBDecrypt(key, ct)
			if err != nil {
				t.Fatalf("aesECBDecrypt: %v", err)
			}
			if !bytes.Equal(got, pt) {
				t.Fatalf("round trip mismatch: got %x want %x", got, pt)
			}
		})
	}
}

func TestAESECB_EncryptPadsToBlockSize(t *testing.T) {
	t.Parallel()
	key := bytes.Repeat([]byte{1}, aes.BlockSize)
	ct, err := aesECBEncrypt(key, []byte("abc")) // 3 字节 -> 填充后 16 字节
	if err != nil {
		t.Fatalf("aesECBEncrypt: %v", err)
	}
	if len(ct) != aes.BlockSize {
		t.Fatalf("ciphertext = %d bytes, want %d", len(ct), aes.BlockSize)
	}
	// 整块输入 -> 追加一个填充块。
	ct2, err := aesECBEncrypt(key, bytes.Repeat([]byte{0}, aes.BlockSize))
	if err != nil {
		t.Fatalf("aesECBEncrypt: %v", err)
	}
	if len(ct2) != 2*aes.BlockSize {
		t.Fatalf("full-block ciphertext = %d bytes, want %d", len(ct2), 2*aes.BlockSize)
	}
}

func TestAESECB_DecryptRejectsBadLength(t *testing.T) {
	t.Parallel()
	key := bytes.Repeat([]byte{2}, aes.BlockSize)
	cases := []int{0, 5, aes.BlockSize - 1, aes.BlockSize + 1}
	for _, n := range cases {
		n := n
		t.Run("len="+strconv.Itoa(n), func(t *testing.T) {
			t.Parallel()
			_, err := aesECBDecrypt(key, make([]byte, n))
			if !errors.Is(err, ErrBadCiphertext) {
				t.Fatalf("err = %v, want ErrBadCiphertext", err)
			}
		})
	}
}

func TestAESECB_DecryptRejectsBadPadding(t *testing.T) {
	t.Parallel()
	key := bytes.Repeat([]byte{3}, aes.BlockSize)
	// 一个分组、填充正确（0x10）的合法密文……
	good, err := aesECBEncrypt(key, bytes.Repeat([]byte{4}, aes.BlockSize-1))
	if err != nil {
		t.Fatalf("aesECBEncrypt: %v", err)
	}
	// ……然后篡改末尾填充字节，使填充校验必然失败。
	bad := append([]byte(nil), good...)
	bad[len(bad)-1] ^= 0xFF
	_, err = aesECBDecrypt(key, bad)
	if !errors.Is(err, ErrBadCiphertext) {
		t.Fatalf("err = %v, want ErrBadCiphertext", err)
	}
}

func TestAESECB_KeySizesAccepted(t *testing.T) {
	t.Parallel()
	// AES-128 需要 16 字节密钥。验证超范围的密钥会被拒绝。
	if _, err := aesECBEncrypt(bytes.Repeat([]byte{1}, aes.BlockSize-1), []byte("x")); err == nil {
		t.Fatal("short key: expected error, got nil")
	}
	if _, err := aesECBEncrypt(bytes.Repeat([]byte{1}, aes.BlockSize+1), []byte("x")); err == nil {
		t.Fatal("long key: expected error, got nil")
	}
}

func TestPKCS7_UnpadRejectsInvalid(t *testing.T) {
	t.Parallel()
	// 填充字节多于一个分组。
	if _, err := pkcs7Unpad([]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 17}, 16); !errors.Is(err, ErrBadCiphertext) {
		t.Fatalf("oversize pad: err = %v, want ErrBadCiphertext", err)
	}
	// 填充字节为 0 永远非法。
	if _, err := pkcs7Unpad([]byte{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 0}, 16); !errors.Is(err, ErrBadCiphertext) {
		t.Fatalf("zero pad: err = %v, want ErrBadCiphertext", err)
	}
}