refactor: extract pkg/charset and internal/event packages

Extract ConvertChunk/FormatHexFrame into pkg/charset (zero external deps).
Extract UIEvent/UIEventKind/UIPanelKind types into internal/event.
Update all references across main package to use qualified imports.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

pkg/charset/charset.go

@@ -0,0 +1,43 @@
+// Package charset provides character-set conversion and hex formatting utilities.
+package charset
+
+import (
+	"bytes"
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/zimolab/charsetconv"
+)
+
+// ConvertChunk converts a byte chunk from srcCode charset to dstCode charset.
+// Returns nil, nil when input is empty. Returns a copied slice when charsets match.
+func ConvertChunk(chunk []byte, srcCode, dstCode string) ([]byte, error) {
+	if len(chunk) == 0 {
+		return nil, nil
+	}
+
+	if strings.EqualFold(srcCode, dstCode) {
+		dup := make([]byte, len(chunk))
+		copy(dup, chunk)
+		return dup, nil
+	}
+
+	var buf bytes.Buffer
+	err := charsetconv.ConvertWith(bytes.NewReader(chunk), charsetconv.Charset(srcCode), &buf, charsetconv.Charset(dstCode), false)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+// FormatHexFrame formats a byte frame as hex + printable representation.
+// Optionally prefixes with a timestamp using the given format string.
+func FormatHexFrame(frame []byte, withTimestamp bool, tsFmt string) string {
+	if withTimestamp {
+		return fmt.Sprintf("%v % X %q \n", time.Now().Format(tsFmt), frame, frame)
+	}
+
+	return fmt.Sprintf("% X %q \n", frame, frame)
+}

pkg/charset/charset_test.go

@@ -0,0 +1,93 @@
+package charset
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestConvertChunk(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		out, err := ConvertChunk(nil, "UTF-8", "UTF-8")
+		if err != nil {
+			t.Fatalf("ConvertChunk(nil) unexpected error: %v", err)
+		}
+		if out != nil {
+			t.Fatalf("ConvertChunk(nil) expected nil output")
+		}
+	})
+
+	t.Run("same-charset-copy", func(t *testing.T) {
+		in := []byte("hello")
+		out, err := ConvertChunk(in, "UTF-8", "UTF-8")
+		if err != nil {
+			t.Fatalf("ConvertChunk same charset unexpected error: %v", err)
+		}
+		if !bytes.Equal(out, in) {
+			t.Fatalf("ConvertChunk same charset mismatch got=%q want=%q", out, in)
+		}
+
+		out[0] = 'H'
+		if in[0] != 'h' {
+			t.Fatalf("ConvertChunk should return a copied slice")
+		}
+	})
+}
+
+func TestFormatHexFrame(t *testing.T) {
+	frame := []byte("AB")
+	out := FormatHexFrame(frame, false, "")
+	if !strings.Contains(out, "41 42") {
+		t.Fatalf("FormatHexFrame missing hex bytes: %q", out)
+	}
+	if !strings.Contains(out, "\"AB\"") {
+		t.Fatalf("FormatHexFrame missing quoted bytes: %q", out)
+	}
+
+	outTS := FormatHexFrame([]byte("A"), true, "2006")
+	if !strings.Contains(outTS, "41") || !strings.Contains(outTS, "\"A\"") {
+		t.Fatalf("FormatHexFrame(withTimestamp) malformed output: %q", outTS)
+	}
+}
+
+func TestConvertChunkCharsetConversion(t *testing.T) {
+	t.Run("gbk-to-utf8", func(t *testing.T) {
+		// Chinese "你好" in GBK: 0xC4 0xE3 0xBA 0xC3
+		gbkHello := []byte{0xC4, 0xE3, 0xBA, 0xC3}
+		out, err := ConvertChunk(gbkHello, "GBK", "UTF-8")
+		if err != nil {
+			t.Fatalf("ConvertChunk GBK->UTF-8 unexpected error: %v", err)
+		}
+		if string(out) != "你好" {
+			t.Fatalf("ConvertChunk GBK->UTF-8 got=%q want=%q", string(out), "你好")
+		}
+	})
+
+	t.Run("same-charset-different-case", func(t *testing.T) {
+		in := []byte("hello")
+		out, err := ConvertChunk(in, "utf-8", "UTF-8")
+		if err != nil {
+			t.Fatalf("ConvertChunk case-diff unexpected error: %v", err)
+		}
+		if !bytes.Equal(out, in) {
+			t.Fatalf("ConvertChunk case-diff mismatch got=%q want=%q", out, in)
+		}
+	})
+
+	t.Run("invalid-charset", func(t *testing.T) {
+		_, err := ConvertChunk([]byte("hello"), "INVALID-CHARSET-NAME", "UTF-8")
+		if err == nil {
+			t.Fatalf("ConvertChunk invalid charset should error")
+		}
+	})
+
+	t.Run("empty-input", func(t *testing.T) {
+		out, err := ConvertChunk([]byte{}, "GBK", "UTF-8")
+		if err != nil {
+			t.Fatalf("ConvertChunk empty unexpected error: %v", err)
+		}
+		if out != nil {
+			t.Fatalf("ConvertChunk empty input should return nil")
+		}
+	})
+}