FEATURE: allow searching for oldest topics (#21715)

In some cases reverse chronological can be very important.

- Oldest post by sam
- Oldest topic by sam

Prior to these new filters we had no way of searching for them.

Now the 2 new orders `order:oldest` and `order:oldest_topic` can be used
to find oldest topics and posts

* Update spec/lib/search_spec.rb

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

* Update spec/lib/search_spec.rb

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

---------

Co-authored-by: Alan Guo Xiang Tan <gxtan1990@gmail.com>

lib/search.rb

@@ -1124,12 +1124,24 @@ class Search
       else
         posts = posts.reorder("posts.created_at DESC")
       end
+    elsif @order == :oldest
+      if aggregate_search
+        posts = posts.order("MAX(posts.created_at) ASC")
+      else
+        posts = posts.reorder("posts.created_at ASC")
+      end
     elsif @order == :latest_topic
       if aggregate_search
         posts = posts.order("MAX(topics.created_at) DESC")
       else
         posts = posts.order("topics.created_at DESC")
       end
+    elsif @order == :oldest_topic
+      if aggregate_search
+        posts = posts.order("MAX(topics.created_at) ASC")
+      else
+        posts = posts.order("topics.created_at ASC")
+      end
     elsif @order == :views
       if aggregate_search
         posts = posts.order("MAX(topics.views) DESC")

spec/lib/search_spec.rb

@@ -2002,6 +2002,17 @@ RSpec.describe Search do
       expect(Search.execute("l sam").posts.map(&:id)).to eq([post2.id, post1.id])
     end
 
+    it "can find by oldest" do
+      topic1 = Fabricate(:topic, title: "I do not like that Sam I am")
+      post1 = Fabricate(:post, topic: topic1, raw: "sam is a sam sam sam") # score higher
+
+      topic2 = Fabricate(:topic, title: "I do not like that Sam I am 2", created_at: 5.minutes.ago)
+      post2 = Fabricate(:post, topic: topic2, created_at: 5.minutes.ago)
+
+      expect(Search.execute("sam").posts.map(&:id)).to eq([post1.id, post2.id])
+      expect(Search.execute("sam ORDER:oldest").posts.map(&:id)).to eq([post2.id, post1.id])
+    end
+
     it "can order by topic creation" do
       today = Date.today
       yesterday = 1.day.ago
@@ -2039,6 +2050,13 @@ RSpec.describe Search do
       expect(Search.execute("Topic order:latest_topic").posts.map(&:id)).to eq(
         [category.topic.first_post.id, latest_irrelevant_topic_post.id, old_relevant_topic_post.id],
       )
+
+      # push weight to the front to ensure test is correct and is not just a coincidence
+      latest_irrelevant_topic_post.update!(raw: "Topic Topic Topic")
+
+      expect(Search.execute("Topic order:oldest_topic").posts.map(&:id)).to eq(
+        [old_relevant_topic_post.id, latest_irrelevant_topic_post.id, category.topic.first_post.id],
+      )
     end
 
     it "can order by topic views" do