package cliprdr

import (
	"bytes"
	"encoding/binary"
	"strings"
	"testing"
)

func TestEncodeCFHTMLRoundTrip(t *testing.T) {
	frag := "<p style=\"color:red\">红色 <b>加粗</b></p>"
	data := EncodeCFHTML(frag)

	s := string(data)
	if !strings.HasPrefix(s, "Version:0.9\r\n") {
		t.Fatalf("missing version header: %q", s[:30])
	}
	// 固定头长 105 字节，doc 从 105 开始
	if !strings.HasPrefix(s[105:], "<html><body><!--StartFragment-->") {
		t.Fatalf("html doc should start at offset 105 with wrapper prefix")
	}
	// 偏移字段自洽（10 位零填充、字节偏移）
	expect := func(key string, want int) {
		i := strings.Index(s, key)
		if i < 0 {
			t.Fatalf("missing %s", key)
		}
		v := 0
		for _, c := range s[i+len(key) : i+len(key)+10] {
			if c < '0' || c > '9' {
				t.Fatalf("%s offset not 10-digit: %q", key, s[i+len(key):i+len(key)+10])
			}
			v = v*10 + int(c-'0')
		}
		if v != want {
			t.Fatalf("%s=%d, want %d", key, v, want)
		}
	}
	expect("StartHTML:", 105)
	expect("EndHTML:", len(data))
	expect("StartFragment:", 105+len(cfHTMLWrapPrefix))
	expect("EndFragment:", len(data)-len(cfHTMLWrapSuffix))

	// 往返
	if got := DecodeCFHTML(data); got != frag {
		t.Fatalf("round-trip mismatch:\n got %q\nwant %q", got, frag)
	}
	// 二进制读取不消费编码流（防御：编码流是文本格式）
	var n uint32
	if err := binary.Read(bytes.NewReader(data[:4]), binary.LittleEndian, &n); err != nil {
		t.Fatalf("binary sanity: %v", err)
	}
}

func TestDecodeCFHTMLWindowsSample(t *testing.T) {
	// 模拟 Windows 剪贴板的实际字节流（头部 + 文档），含 UTF-8 中文
	frag := "<p>hello \xe4\xb8\xad\xe6\x96\x87</p>"
	doc := "<html><body><!--StartFragment-->" + frag + "<!--EndFragment--></body></html>"
	var buf bytes.Buffer
	buf.WriteString("Version:0.9\r\nStartHTML:0000000105\r\n")
	endHTML := 105 + len(doc)
	buf.WriteString("EndHTML:" + pad10(endHTML) + "\r\n")
	startFragment := 105 + len(cfHTMLWrapPrefix)
	buf.WriteString("StartFragment:" + pad10(startFragment) + "\r\n")
	endFragment := startFragment + len(frag)
	buf.WriteString("EndFragment:" + pad10(endFragment) + "\r\n")
	buf.WriteString(doc)

	got := DecodeCFHTML(buf.Bytes())
	if got != frag {
		t.Fatalf("decode mismatch:\n got %q\nwant %q", got, frag)
	}
}

func TestDecodeCFHTMLFallback(t *testing.T) {
	// 无有效头的乱数据：回退为原样返回，不得 panic
	got := DecodeCFHTML([]byte("not a cf_html stream"))
	if got != "not a cf_html stream" {
		t.Fatalf("fallback changed content: %q", got)
	}
}

func pad10(v int) string {
	s := itoa10(v)
	if len(s) > 10 {
		s = s[len(s)-10:]
	}
	for len(s) < 10 {
		s = "0" + s
	}
	return s
}

func itoa10(v int) string {
	if v == 0 {
		return "0"
	}
	var b []byte
	for v > 0 {
		b = append([]byte{byte('0' + v%10)}, b...)
		v /= 10
	}
	return string(b)
}