feat: navigate individual sections

internal/note/sections.go

@@ -0,0 +1,103 @@
+package note
+
+import (
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+type Section struct {
+	ID      string
+	Heading string
+	Content string
+}
+
+// ParseH2Heading returns the heading text for a level-two markdown heading.
+func ParseH2Heading(line string) (string, bool) {
+	trimmed := strings.TrimLeft(line, " \t")
+	if !strings.HasPrefix(trimmed, "## ") {
+		return "", false
+	}
+	return strings.TrimSpace(strings.TrimPrefix(trimmed, "## ")), true
+}
+
+// ParseSections splits markdown into level-two heading sections.
+func ParseSections(content string) []Section {
+	if content == "" {
+		return nil
+	}
+
+	lines := strings.Split(content, "\n")
+	var sections []Section
+
+	var current *Section
+	var builder strings.Builder
+	counts := make(map[string]int)
+
+	flush := func() {
+		if current == nil {
+			return
+		}
+		current.Content = builder.String()
+		sections = append(sections, *current)
+		current = nil
+		builder.Reset()
+	}
+
+	for i, line := range lines {
+		heading, ok := ParseH2Heading(line)
+		if ok {
+			flush()
+			base := slugifyHeading(heading)
+			if base == "" {
+				base = "section"
+			}
+			counts[base]++
+			id := base
+			if counts[base] > 1 {
+				id = base + "-" + strconv.Itoa(counts[base])
+			}
+			current = &Section{
+				ID:      id,
+				Heading: heading,
+			}
+		}
+
+		if current != nil {
+			builder.WriteString(line)
+			if i < len(lines)-1 {
+				builder.WriteString("\n")
+			}
+		}
+	}
+
+	flush()
+	return sections
+}
+
+func slugifyHeading(input string) string {
+	in := strings.TrimSpace(strings.ToLower(input))
+	if in == "" {
+		return ""
+	}
+
+	var b strings.Builder
+	prevDash := false
+
+	for _, r := range in {
+		if unicode.IsLetter(r) || unicode.IsDigit(r) {
+			b.WriteRune(r)
+			prevDash = false
+			continue
+		}
+
+		if !prevDash {
+			b.WriteByte('-')
+			prevDash = true
+		}
+	}
+
+	out := b.String()
+	out = strings.Trim(out, "-")
+	return out
+}

internal/note/sections_test.go

@@ -0,0 +1,69 @@
+package note
+
+import "testing"
+
+func TestSlugifyHeading(t *testing.T) {
+	cases := []struct {
+		name  string
+		input string
+		want  string
+	}{
+		{name: "simple", input: "Glossary", want: "glossary"},
+		{name: "date and title", input: "2026-01-01 - First", want: "2026-01-01-first"},
+		{name: "punctuation", input: "Hello, World!", want: "hello-world"},
+		{name: "trim", input: "  spaced   out  ", want: "spaced-out"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := slugifyHeading(tc.input); got != tc.want {
+				t.Fatalf("expected %q, got %q", tc.want, got)
+			}
+		})
+	}
+}
+
+func TestParseSections(t *testing.T) {
+	content := "# Title\nIntro\n## Alpha\nA1\nA2\n## Beta\nB1\n"
+
+	sections := ParseSections(content)
+	if len(sections) != 2 {
+		t.Fatalf("expected 2 sections, got %d", len(sections))
+	}
+
+	if sections[0].Heading != "Alpha" {
+		t.Fatalf("expected first heading Alpha, got %q", sections[0].Heading)
+	}
+	if sections[0].ID != "alpha" {
+		t.Fatalf("expected first id alpha, got %q", sections[0].ID)
+	}
+	if want := "## Alpha\nA1\nA2\n"; sections[0].Content != want {
+		t.Fatalf("expected first content %q, got %q", want, sections[0].Content)
+	}
+
+	if sections[1].Heading != "Beta" {
+		t.Fatalf("expected second heading Beta, got %q", sections[1].Heading)
+	}
+	if sections[1].ID != "beta" {
+		t.Fatalf("expected second id beta, got %q", sections[1].ID)
+	}
+	if want := "## Beta\nB1\n"; sections[1].Content != want {
+		t.Fatalf("expected second content %q, got %q", want, sections[1].Content)
+	}
+}
+
+func TestParseSections_DuplicateHeadings(t *testing.T) {
+	content := "## Glossary\nTerm A\n## Glossary\nTerm B\n"
+
+	sections := ParseSections(content)
+	if len(sections) != 2 {
+		t.Fatalf("expected 2 sections, got %d", len(sections))
+	}
+
+	if sections[0].ID != "glossary" {
+		t.Fatalf("expected first id glossary, got %q", sections[0].ID)
+	}
+	if sections[1].ID != "glossary-2" {
+		t.Fatalf("expected second id glossary-2, got %q", sections[1].ID)
+	}
+}