DEV: A rake task to generate topics (#1171)

Adds a new rake task to generate topics using the AI helper model.

Generate topics using 
```
bundle exec rake "ai:generate_topics[Don Quijote de la Mancha\, Cien años de soledad\, Os Lusíadas\,三国演义]"
```

For now it randomly chooses a non-read-restricted category and a random bunch of users.

lib/tasks/create_topics.rake

@@ -0,0 +1,101 @@
+# frozen_string_literal: true
+
+namespace :ai do
+  desc "Generate topics with AI post content using random users and categories. Use it this way rake ai:generate_topics['title1\,title2\,title3']"
+  task :generate_topics, [:titles] => [:environment] do |task, args|
+    titles = args[:titles].include?(",") ? args[:titles].split(",").map(&:strip) : [args[:titles]]
+    puts "Will create #{titles.size} #{"topics".pluralize(titles.size)}: #{titles.join(", ")}"
+
+    titles.each do |title|
+      next if Topic.find_by_title(TextCleaner.clean_title(TextSentinel.title_sentinel(title).text))
+      category =
+        Category
+          .where.not(id: SiteSetting.uncategorized_category_id)
+          .where(read_restricted: false)
+          .order("RANDOM()")
+          .first
+      users = User.real.activated.not_suspended.where(staged: false).order("RANDOM()").limit(12)
+      RateLimiter.disable
+
+      creator = TopicGenerator.new(title)
+      first_post = creator.get_first_post
+      replies_count = rand(4..10)
+      replies = creator.get_replies(replies_count)
+
+      post = create_topic(category, first_post, title, users)
+      replies.each_with_index { |reply, i| create_post(users[i + 1], post.topic_id, reply) }
+      puts "'#{title}' has #{replies.size} replies"
+    end
+  end
+
+  def create_topic(category, first_post, title, users)
+    puts "#{users.first.username} will create topic '#{title}' in category '#{category.name}'"
+    post =
+      PostCreator.create!(
+        users.first,
+        title: title,
+        raw: first_post,
+        category: category.id,
+        skip_guardian: true,
+      )
+    puts "Created topic '#{title}' (#{post.topic_id}) in category '#{category.name}'"
+    post
+  end
+
+  def create_post(user, topic_id, raw)
+    puts "#{user.username} will reply to topic #{topic_id}"
+    PostCreator.create!(user, topic_id:, raw:, skip_guardian: true)
+  end
+
+  class TopicGenerator
+    def initialize(title)
+      @title = title
+    end
+
+    def get_first_post
+      TopicGenerator.generate(<<~PROMPT)
+        Write and opening topic about title: #{@title}.
+        - content must be in the same language as title
+        - content in markdown
+        - content should exclude the title
+        - maximum of 200 words
+      PROMPT
+    end
+
+    def get_replies(count)
+      JSON.parse(
+        TopicGenerator.generate(<<~PROMPT).gsub(/```json\n?|\```/, "").gsub(/,\n\n/, ",\n").strip,
+                Write #{count} replies to a topic with title #{@title}.
+                - respond in an array of strings within double quotes ["", "", ""]
+                - each with a maximum of 100 words
+                - keep to same language of title
+                - each reply may contain markdown to bold, italicize, link, or bullet point
+                - do not return anything else other than the array
+                - the last item in the array should not have a trailing comma
+                - Example return value ["I agree with you. So and so...", "It is fun ... etc"]
+              PROMPT
+      )
+    end
+
+    private
+
+    def self.generate(prompt)
+      return "" if prompt.blank?
+
+      prompt =
+        DiscourseAi::Completions::Prompt.new(
+          "You are a forum user writing concise, informative posts. Keep responses focused and natural.",
+          messages: [{ type: :user, content: prompt, id: "user" }],
+        )
+
+      DiscourseAi::Completions::Llm.proxy(SiteSetting.ai_helper_model).generate(
+        prompt,
+        user: Discourse.system_user,
+        feature_name: "topic-generator",
+      )
+    rescue => e
+      Rails.logger.error("AI TopicGenerator Error: #{e.message}")
+      ""
+    end
+  end
+end