Add category pkg

This supports categories in Write.as / WriteFreely.

Ref T809

category/category.go

@@ -0,0 +1,30 @@
+// Package category supports post categories
+package category
+
+import (
+	"errors"
+	"github.com/writeas/slug"
+)
+
+var (
+	ErrNotFound = errors.New("category doesn't exist")
+)
+
+// Category represents a post tag with additional metadata, like a title and slug.
+type Category struct {
+	ID      int64  `json:"-"`
+	Hashtag string `json:"hashtag"`
+	Slug    string `json:"slug"`
+	Title   string `json:"title"`
+}
+
+// NewCategory creates a Category you can insert into the database, based on a hashtag. It automatically breaks up the
+// hashtag by words, based on capitalization, for both the title and a URL-friendly slug.
+func NewCategory(hashtag string) *Category {
+	title := titleFromHashtag(hashtag)
+	return &Category{
+		Hashtag: hashtag,
+		Slug:    slug.Make(title),
+		Title:   title,
+	}
+}

category/tags.go

@@ -0,0 +1,26 @@
+package category
+
+import (
+	"strings"
+	"unicode"
+)
+
+// titleFromHashtag generates an all-lowercase title, with spaces inserted based on initial capitalization -- e.g.
+// "MyWordyTag" becomes "my wordy tag".
+func titleFromHashtag(hashtag string) string {
+	var t strings.Builder
+	var prev rune
+	for i, c := range hashtag {
+		if unicode.IsUpper(c) {
+			if i > 0 && !unicode.IsUpper(prev) {
+				// Insert space if previous rune wasn't also uppercase (e.g. an abbreviation)
+				t.WriteRune(' ')
+			}
+			t.WriteRune(unicode.ToLower(c))
+		} else {
+			t.WriteRune(c)
+		}
+		prev = c
+	}
+	return t.String()
+}

category/tags_test.go

@@ -0,0 +1,31 @@
+package category
+
+import "testing"
+
+func TestTitleFromHashtag(t *testing.T) {
+	tests := []struct {
+		name     string
+		hashtag  string
+		expTitle string
+	}{
+		{"proper noun", "Jane", "jane"},
+		{"full name", "JaneDoe", "jane doe"},
+		{"us words", "unitedStates", "united states"},
+		{"usa", "USA", "usa"},
+		{"us monoword", "unitedstates", "unitedstates"},
+		{"100dto", "100DaysToOffload", "100 days to offload"},
+		{"iphone", "iPhone", "iphone"},
+		{"ilike", "iLikeThis", "i like this"},
+		{"abird", "aBird", "a bird"},
+		{"all caps", "URGENT", "urgent"},
+		{"smartphone", "スマートフォン", "スマートフォン"},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			res := titleFromHashtag(test.hashtag)
+			if res != test.expTitle {
+				t.Fatalf("#%s: got '%s' expected '%s'", test.hashtag, res, test.expTitle)
+			}
+		})
+	}
+}