Correct the article in generated documents

For example:

  "a Ingress" > "an Ingress"

pkg/util/strings/strings.go

@@ -17,8 +17,10 @@ limitations under the License.
 package strings
 
 import (
+	"fmt"
 	"path"
 	"strings"
+	"unicode"
 )
 
 // Splits a fully qualified name and returns its namespace and name.
@@ -45,3 +47,30 @@ func ShortenString(str string, n int) string {
 		return str[:n]
 	}
 }
+
+// GetArticleForNoun returns the article needed for the given noun.
+func GetArticleForNoun(noun string, padding string) string {
+	if noun[len(noun)-2:] != "ss" && noun[len(noun)-1:] == "s" {
+		// Plurals don't have an article.
+		// Don't catch words like class
+		return fmt.Sprintf("%v", padding)
+	}
+
+	article := "a"
+	if isVowel(rune(noun[0])) {
+		article = "an"
+	}
+
+	return fmt.Sprintf("%s%s%s", padding, article, padding)
+}
+
+// isVowel returns true if the rune is a vowel (case insensitive).
+func isVowel(c rune) bool {
+	vowels := []rune{'a', 'e', 'i', 'o', 'u'}
+	for _, value := range vowels {
+		if value == unicode.ToLower(c) {
+			return true
+		}
+	}
+	return false
+}

pkg/util/strings/strings_test.go

@@ -71,3 +71,73 @@ func TestShortenString(t *testing.T) {
 		}
 	}
 }
+
+func TestIsVowel(t *testing.T) {
+	tests := []struct {
+		name string
+		arg  rune
+		want bool
+	}{
+		{
+			name: "yes",
+			arg:  'E',
+			want: true,
+		},
+		{
+			name: "no",
+			arg:  'n',
+			want: false,
+		},
+	}
+	for _, tt := range tests {
+		if got := isVowel(tt.arg); got != tt.want {
+			t.Errorf("%q. IsVowel() = %v, want %v", tt.name, got, tt.want)
+		}
+	}
+}
+
+func TestGetArticleForNoun(t *testing.T) {
+	type args struct {
+	}
+	tests := []struct {
+		noun    string
+		padding string
+		want    string
+	}{
+		{
+			noun:    "Frog",
+			padding: " ",
+			want:    " a ",
+		},
+		{
+			noun:    "frogs",
+			padding: " ",
+			want:    " ",
+		},
+		{
+			noun:    "apple",
+			padding: "",
+			want:    "an",
+		},
+		{
+			noun:    "Apples",
+			padding: " ",
+			want:    " ",
+		},
+		{
+			noun:    "Ingress",
+			padding: " ",
+			want:    " an ",
+		},
+		{
+			noun:    "Class",
+			padding: " ",
+			want:    " a ",
+		},
+	}
+	for _, tt := range tests {
+		if got := GetArticleForNoun(tt.noun, tt.padding); got != tt.want {
+			t.Errorf("%q. GetArticleForNoun() = %v, want %v", tt.noun, got, tt.want)
+		}
+	}
+}