feat: properly handle repeated heading text

README.md

@@ -7,7 +7,7 @@ Generate a table of contents for an existing markdown document. The table of con
   * [Installation](#installation)
   * [Usage](#usage)
 * [Library](#library)
-  * [Usage](#usage-2)
+  * [Usage](#usage-1)
 <!---mdtoc end--->
 ## CLI
 

testdata/repeat.md

@@ -0,0 +1,8 @@
+# Title
+An example document with repeated heading text to verify link generation handles this properly.
+
+## Testing
+### Testing
+#### Testing
+### Testing
+## Testing

testdata/repeat_toc.md

@@ -0,0 +1,15 @@
+# Title
+An example document with repeated heading text to verify link generation handles this properly.
+
+<!---mdtoc begin--->
+* [Testing](#testing)
+  * [Testing](#testing-1)
+    * [Testing](#testing-2)
+  * [Testing](#testing-3)
+* [Testing](#testing-4)
+<!---mdtoc end--->
+## Testing
+### Testing
+#### Testing
+### Testing
+## Testing

toc.go

@@ -126,6 +126,7 @@ func Parse(b []byte) (*Toc, error) {
 		return &toc, err
 	}
 
+	toc.updateRepeatLinks()
 	return &toc, nil
 }
 
@@ -137,3 +138,23 @@ func textToLink(s string) string {
 	rep := strings.NewReplacer(" ", "-", "/", "", ",", "", ".", "", "+", "", ":", "", ";", "")
 	return strings.ToLower(rep.Replace(s))
 }
+
+// updateRepeatLinks fixes the generated link text if the generated text is repeated
+// in the same contents
+func (t *Toc) updateRepeatLinks() {
+	lookup := make(map[string]int, len(t.Bullets))
+
+	for i, b := range t.Bullets {
+		// if key already exists in the lookup, the  link text needs to append a `-n`,
+		// where `n` is the number of previous occurences. if the key does not already
+		// exist, add a new key and set occurences to 1.
+		if val, ok := lookup[b.Link]; ok {
+			key := b.Link // preserve the original lookup key
+			t.Bullets[i].Link = fmt.Sprintf("%s-%d", b.Link, val)
+			lookup[key]++
+			continue
+		}
+
+		lookup[b.Link] = 1
+	}
+}

toc_test.go

@@ -12,6 +12,8 @@ func TestAdd(t *testing.T) {
 	basicToc, _ := os.ReadFile("testdata/basic_toc.md")
 	special, _ := os.ReadFile("testdata/special.md")
 	specialToc, _ := os.ReadFile("testdata/special_toc.md")
+	repeat, _ := os.ReadFile("testdata/repeat.md")
+	repeatToc, _ := os.ReadFile("testdata/repeat_toc.md")
 
 	tt := []struct {
 		name    string
@@ -22,6 +24,7 @@ func TestAdd(t *testing.T) {
 	}{
 		{"basic", basic, false, basicToc, nil},
 		{"special", special, false, specialToc, nil},
+		{"repeat", repeat, false, repeatToc, nil},
 		{"existing without force", basicToc, false, nil, ErrExistingToc},
 		{"existing with force", basicToc, true, basicToc, nil},
 	}