feat: 広場のページネーション（#169） (#189)

#169 バグ修正

Merge remote-tracking branch 'origin/main' into feature/169

#169

Co-authored-by: miteruzo <miteruzo@naver.com>
Reviewed-on: #189

backend/app/controllers/posts_controller.rb

@@ -3,20 +3,35 @@ class PostsController < ApplicationController
 
   # GET /posts
   def index
-    limit = params[:limit].presence&.to_i
+    page = (params[:page].presence || 1).to_i
+    limit = (params[:limit].presence || 20).to_i
     cursor = params[:cursor].presence
 
-    created_at = ('COALESCE(posts.original_created_before - INTERVAL 1 SECOND,' +
-                  'posts.original_created_from,' +
-                  'posts.created_at)')
-    q = filtered_posts.order(Arel.sql("#{ created_at } DESC"))
-    q = q.where("#{ created_at } < ?", Time.iso8601(cursor)) if cursor
+    page = 1 if page < 1
+    limit = 1 if limit < 1
 
-    posts = limit ? q.limit(limit + 1) : q
+    offset = (page - 1) * limit
+
+    sort_sql =
+        'COALESCE(posts.original_created_before - INTERVAL 1 SECOND,' +
+        'posts.original_created_from,' +
+        'posts.created_at)'
+    q =
+        filtered_posts
+        .preload(:tags)
+        .with_attached_thumbnail
+        .select("posts.*, #{ sort_sql } AS sort_ts")
+        .order(Arel.sql("#{ sort_sql } DESC"))
+    posts = (
+        if cursor
+          q.where("#{ sort_sql } < ?", Time.iso8601(cursor)).limit(limit + 1)
+        else
+          q.limit(limit).offset(offset)
+        end).to_a
 
     next_cursor = nil
-    if limit && posts.size > limit
-      next_cursor = posts.last.created_at.iso8601(6)
+    if cursor && posts.length > limit
+      next_cursor = posts.last.read_attribute('sort_ts').iso8601(6)
       posts = posts.first(limit)
     end
 
@@ -29,7 +44,7 @@ class PostsController < ApplicationController
               nil
             end
       end
-    }, next_cursor: }
+    }, count: filtered_posts.count(:id), next_cursor: }
   end
 
   def random