feat: style ranges (#458)

* feat: style ranges

Extracted from charmbracelet/gum#789 , this
allows to style ranges of a given string without breaking its current
styles.

The resulting ansi sequences aren't that beautiful (as there might be
many styles+reset with nothing in them), but it works. We can optimize
this later I think.

* fix: wide characters

* feat: helper to style a single range

* chore: review

Author: caarlos0

go.mod

@@ -8,7 +8,7 @@ go 1.18
 
 require (
 	github.com/aymanbagabas/go-udiff v0.2.0
-	github.com/charmbracelet/x/ansi v0.6.0
+	github.com/charmbracelet/x/ansi v0.6.1-0.20250107110353-48b574af22a5
 	github.com/charmbracelet/x/exp/golden v0.0.0-20240806155701-69247e0abc2a
 	github.com/muesli/termenv v0.15.2
 	github.com/rivo/uniseg v0.4.7

go.sum

@@ -2,8 +2,8 @@ github.com/aymanbagabas/go-osc52/v2 v2.0.1 h1:HwpRHbFMcZLEVr42D4p7XBqjyuxQH5SMiE
 github.com/aymanbagabas/go-osc52/v2 v2.0.1/go.mod h1:uYgXzlJ7ZpABp8OJ+exZzJJhRNQ2ASbcXHWsFqH8hp8=
 github.com/aymanbagabas/go-udiff v0.2.0 h1:TK0fH4MteXUDspT88n8CKzvK0X9O2xu9yQjWpi6yML8=
 github.com/aymanbagabas/go-udiff v0.2.0/go.mod h1:RE4Ex0qsGkTAJoQdQQCA0uG+nAzJO/pI/QwceO5fgrA=
-github.com/charmbracelet/x/ansi v0.6.0 h1:qOznutrb93gx9oMiGf7caF7bqqubh6YIM0SWKyA08pA=
-github.com/charmbracelet/x/ansi v0.6.0/go.mod h1:KBUFw1la39nl0dLl10l5ORDAqGXaeurTQmwyyVKse/Q=
+github.com/charmbracelet/x/ansi v0.6.1-0.20250107110353-48b574af22a5 h1:TSjbA80sXnABV/Vxhnb67Ho7p8bEYqz6NIdhLAx+1yg=
+github.com/charmbracelet/x/ansi v0.6.1-0.20250107110353-48b574af22a5/go.mod h1:KBUFw1la39nl0dLl10l5ORDAqGXaeurTQmwyyVKse/Q=
 github.com/charmbracelet/x/exp/golden v0.0.0-20240806155701-69247e0abc2a h1:G99klV19u0QnhiizODirwVksQB91TJKV/UaTnACcG30=
 github.com/charmbracelet/x/exp/golden v0.0.0-20240806155701-69247e0abc2a/go.mod h1:wDlXFlCrmJ8J+swcL/MnGUuYnqgQdW9rhSD61oNMb6U=
 github.com/lucasb-eyer/go-colorful v1.2.0 h1:1nnpGOrhyZZuNyfu1QjKiUICQ74+3FNCN69Aj6K7nkY=

ranges.go

@@ -0,0 +1,48 @@
+package lipgloss
+
+import (
+	"strings"
+
+	"github.com/charmbracelet/x/ansi"
+)
+
+// StyleRanges allows to, given a string, style ranges of it differently.
+// The function will take into account existing styles.
+// Ranges should not overlap.
+func StyleRanges(s string, ranges ...Range) string {
+	if len(ranges) == 0 {
+		return s
+	}
+
+	var buf strings.Builder
+	lastIdx := 0
+	stripped := ansi.Strip(s)
+
+	// Use Truncate and TruncateLeft to style match.MatchedIndexes without
+	// losing the original option style:
+	for _, rng := range ranges {
+		// Add the text before this match
+		if rng.Start > lastIdx {
+			buf.WriteString(ansi.Cut(s, lastIdx, rng.Start))
+		}
+		// Add the matched range with its highlight
+		buf.WriteString(rng.Style.Render(ansi.Cut(stripped, rng.Start, rng.End)))
+		lastIdx = rng.End
+	}
+
+	// Add any remaining text after the last match
+	buf.WriteString(ansi.TruncateLeft(s, lastIdx, ""))
+
+	return buf.String()
+}
+
+// NewRange returns a range that can be used with [StyleRanges].
+func NewRange(start, end int, style Style) Range {
+	return Range{start, end, style}
+}
+
+// Range to be used with [StyleRanges].
+type Range struct {
+	Start, End int
+	Style      Style
+}

ranges_test.go

@@ -0,0 +1,102 @@
+package lipgloss
+
+import (
+	"testing"
+
+	"github.com/muesli/termenv"
+)
+
+func TestStyleRanges(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		ranges   []Range
+		expected string
+	}{
+		{
+			name:     "empty ranges",
+			input:    "hello world",
+			ranges:   []Range{},
+			expected: "hello world",
+		},
+		{
+			name:  "single range in middle",
+			input: "hello world",
+			ranges: []Range{
+				NewRange(6, 11, NewStyle().Bold(true)),
+			},
+			expected: "hello \x1b[1mworld\x1b[0m",
+		},
+		{
+			name:  "multiple ranges",
+			input: "hello world",
+			ranges: []Range{
+				NewRange(0, 5, NewStyle().Bold(true)),
+				NewRange(6, 11, NewStyle().Italic(true)),
+			},
+			expected: "\x1b[1mhello\x1b[0m \x1b[3mworld\x1b[0m",
+		},
+		{
+			name:  "overlapping with existing ANSI",
+			input: "hello \x1b[32mworld\x1b[0m",
+			ranges: []Range{
+				NewRange(0, 5, NewStyle().Bold(true)),
+			},
+			expected: "\x1b[1mhello\x1b[0m \x1b[32mworld\x1b[0m",
+		},
+		{
+			name:  "style at start",
+			input: "hello world",
+			ranges: []Range{
+				NewRange(0, 5, NewStyle().Bold(true)),
+			},
+			expected: "\x1b[1mhello\x1b[0m world",
+		},
+		{
+			name:  "style at end",
+			input: "hello world",
+			ranges: []Range{
+				NewRange(6, 11, NewStyle().Bold(true)),
+			},
+			expected: "hello \x1b[1mworld\x1b[0m",
+		},
+		{
+			name:  "multiple styles with gap",
+			input: "hello beautiful world",
+			ranges: []Range{
+				NewRange(0, 5, NewStyle().Bold(true)),
+				NewRange(16, 23, NewStyle().Italic(true)),
+			},
+			expected: "\x1b[1mhello\x1b[0m beautiful \x1b[3mworld\x1b[0m",
+		},
+		{
+			name:  "adjacent ranges",
+			input: "hello world",
+			ranges: []Range{
+				NewRange(0, 5, NewStyle().Bold(true)),
+				NewRange(6, 11, NewStyle().Italic(true)),
+			},
+			expected: "\x1b[1mhello\x1b[0m \x1b[3mworld\x1b[0m",
+		},
+		{
+			name:  "wide-width characters",
+			input: "Hello 你好 世界",
+			ranges: []Range{
+				NewRange(0, 5, NewStyle().Bold(true)),    // "Hello"
+				NewRange(7, 10, NewStyle().Italic(true)), // "你好"
+				NewRange(11, 50, NewStyle().Bold(true)),  // "世界"
+			},
+			expected: "\x1b[1mHello\x1b[0m \x1b[3m你好\x1b[0m \x1b[1m世界\x1b[0m",
+		},
+	}
+
+	for _, tt := range tests {
+		renderer.SetColorProfile(termenv.ANSI)
+		t.Run(tt.name, func(t *testing.T) {
+			result := StyleRanges(tt.input, tt.ranges...)
+			if result != tt.expected {
+				t.Errorf("StyleRanges()\n got = %q\nwant = %q\n", result, tt.expected)
+			}
+		})
+	}
+}