Add tag selector to index

srv/src/http/index.go

@@ -30,7 +30,19 @@ func (a *api) renderIndexHandler() http.Handler {
 			return
 		}
 
-		posts, hasMore, err := a.params.PostStore.Get(page, pageCount)
+		tag := r.FormValue("tag")
+
+		var (
+			posts   []post.StoredPost
+			hasMore bool
+		)
+
+		if tag == "" {
+			posts, hasMore, err = a.params.PostStore.Get(page, pageCount)
+		} else {
+			posts, err = a.params.PostStore.GetByTag(tag)
+		}
+
 		if err != nil {
 			apiutil.InternalServerError(
 				rw, r, fmt.Errorf("fetching page %d of posts: %w", page, err),
@@ -38,13 +50,23 @@ func (a *api) renderIndexHandler() http.Handler {
 			return
 		}
 
+		tags, err := a.params.PostStore.GetTags()
+		if err != nil {
+			apiutil.InternalServerError(
+				rw, r, fmt.Errorf("fething tags: %w", err),
+			)
+			return
+		}
+
 		tplPayload := struct {
 			Posts              []post.StoredPost
 			PrevPage, NextPage int
+			Tags               []string
 		}{
 			Posts:    posts,
 			PrevPage: -1,
 			NextPage: -1,
+			Tags:     tags,
 		}
 
 		if page > 0 {

srv/src/http/tpl/index.html

@@ -1,5 +1,12 @@
 {{ define "body" }}
 
+  <p>
+    By Tag:
+    {{ range .Payload.Tags }}
+    <a href="{{ BlogURL "/" }}?tag={{ . }}">{{ . }}</a>
+    {{ end }}
+  </p>
+
   <ul id="posts-list">
 
     {{ range .Payload.Posts }}

srv/src/post/post.go

@@ -68,6 +68,9 @@ type Store interface {
 	// descending, or empty slice.
 	GetByTag(tag string) ([]StoredPost, error)
 
+	// GetTags returns all tags which have at least one Post using them.
+	GetTags() ([]string, error)
+
 	// Delete will delete the StoredPost with the given ID.
 	Delete(id string) error
 }
@@ -340,6 +343,30 @@ func (s *store) GetByTag(tag string) ([]StoredPost, error) {
 	return posts, err
 }
 
+func (s *store) GetTags() ([]string, error) {
+
+	rows, err := s.db.Query(`SELECT tag FROM post_tags GROUP BY tag`)
+	if err != nil {
+		return nil, fmt.Errorf("querying all tags: %w", err)
+	}
+	defer rows.Close()
+
+	var tags []string
+
+	for rows.Next() {
+
+		var tag string
+
+		if err := rows.Scan(&tag); err != nil {
+			return nil, fmt.Errorf("scanning tag: %w", err)
+		}
+
+		tags = append(tags, tag)
+	}
+
+	return tags, nil
+}
+
 func (s *store) Delete(id string) error {
 
 	tx, err := s.db.Begin()

srv/src/post/post_test.go

@@ -252,5 +252,9 @@ func TestStore(t *testing.T) {
 		bazPosts, err := h.store.GetByTag("baz")
 		assert.NoError(t, err)
 		assert.Empty(t, bazPosts)
+
+		tags, err := h.store.GetTags()
+		assert.NoError(t, err)
+		assert.ElementsMatch(t, []string{"foo", "bar"}, tags)
 	})
 }