feat(textutil): add width-aware text wrapping and clipping

Wrap, Clip, and Pad plain text to a fixed rune width for the terminal panes.

internal/textutil/text.go

@@ -0,0 +1,72 @@
+// Package textutil wraps and clips plain text for a fixed terminal width.
+package textutil
+
+import "strings"
+
+// Clip shortens s to at most n runes, replacing tabs and newlines with spaces.
+func Clip(s string, n int) string {
+	if n <= 0 {
+		return ""
+	}
+	s = strings.ReplaceAll(strings.ReplaceAll(s, "\t", " "), "\n", " ")
+	r := []rune(s)
+	if len(r) <= n {
+		return string(r)
+	}
+	if n == 1 {
+		return "…"
+	}
+	return string(r[:n-1]) + "…"
+}
+
+// Wrap breaks s into lines no wider than width runes, preserving blank lines.
+func Wrap(s string, width int) []string {
+	if width <= 1 {
+		if s == "" {
+			return []string{""}
+		}
+		return []string{s}
+	}
+	var out []string
+	for _, para := range strings.Split(s, "\n") {
+		if para == "" {
+			out = append(out, "")
+			continue
+		}
+		line := ""
+		for _, word := range strings.Split(para, " ") {
+			for len([]rune(word)) > width {
+				if line != "" {
+					out = append(out, line)
+					line = ""
+				}
+				r := []rune(word)
+				out = append(out, string(r[:width]))
+				word = string(r[width:])
+			}
+			switch {
+			case line == "":
+				line = word
+			case len([]rune(line))+1+len([]rune(word)) <= width:
+				line += " " + word
+			default:
+				out = append(out, line)
+				line = word
+			}
+		}
+		out = append(out, line)
+	}
+	if len(out) == 0 {
+		return []string{""}
+	}
+	return out
+}
+
+// Pad pads s with spaces on the right until it is n runes wide.
+func Pad(s string, n int) string {
+	r := []rune(s)
+	if len(r) >= n {
+		return string(r)
+	}
+	return string(r) + strings.Repeat(" ", n-len(r))
+}

internal/textutil/text_test.go

@@ -0,0 +1,32 @@
+package textutil
+
+import "testing"
+
+func TestClip(t *testing.T) {
+	if got := Clip("abcdef", 4); got != "abc…" {
+		t.Fatalf("clip: %q", got)
+	}
+	if got := Clip("ab", 4); got != "ab" {
+		t.Fatalf("short: %q", got)
+	}
+	if got := Clip("a\nb", 5); got != "a b" {
+		t.Fatalf("newline: %q", got)
+	}
+}
+
+func TestWrap(t *testing.T) {
+	got := Wrap("one two three", 7)
+	want := []string{"one two", "three"}
+	if len(got) != len(want) {
+		t.Fatalf("wrap %#v", got)
+	}
+	for i := range want {
+		if got[i] != want[i] {
+			t.Fatalf("line %d: %q", i, got[i])
+		}
+	}
+	blank := Wrap("a\n\nb", 10)
+	if len(blank) != 3 || blank[1] != "" {
+		t.Fatalf("blank lines: %#v", blank)
+	}
+}