DEV: Lots of improvements to the generic_bulk import script

Notable changes:
* Imports a lot more tables from core and plugins
  * site settings
  * uploads with necessary upload references
  * groups and group members
  * user profiles
  * user options
  * user fields & values
  * muted users
  * user notes (plugin)
  * user followers (plugin)
  * user avatars
  * tag groups and tags
  * tag users (notification settings for tags / user)
  * category permissions
  * polls with options and votes
  * post votes (plugin)
  * solutions (plugin)
  * gamification scores (plugin)
  * events (plugin)
  * badges and badge groupings
  * user badges
  * optimized images
  * topic users (notification settings for topics)
  * post custom fields
  * permalinks and permalink normalizations

* It creates the `migration_mappings` table which is used to store the mapping for a handful of imported tables

* Detects duplicate group names and renames them

* Pre-cooking for attachments, images and mentions

* Outputs instructions when gems are missing

* Supports importing uploads from a DB generated by `uploads_importer.rb`

* Checks that all required plugins exists and enables them if needed

* A couple of optimizations and additions in `import.rake`

lib/tasks/import.rake

@@ -15,6 +15,7 @@ task "import:ensure_consistency" => :environment do
   insert_user_stats
   insert_user_visits
   insert_draft_sequences
+  insert_automatic_group_users
 
   update_user_stats
   update_posts
@@ -24,8 +25,11 @@ task "import:ensure_consistency" => :environment do
   update_groups
   update_tag_stats
   update_topic_users
+  update_topic_featured_users
   create_category_definitions
 
+  # run_jobs
+
   log "Done!"
 end
 
@@ -213,11 +217,16 @@ end
 def insert_user_stats
   log "Inserting user stats..."
 
-  DB.exec <<-SQL
+  DB.exec <<~SQL
     INSERT INTO user_stats (user_id, new_since)
-         SELECT id, created_at
+    SELECT id, created_at
-           FROM users
+      FROM users u
-    ON CONFLICT DO NOTHING
+     WHERE NOT EXISTS (
+       SELECT 1
+         FROM user_stats us
+        WHERE us.user_id = u.id
+     )
+        ON CONFLICT DO NOTHING
   SQL
 end
 
@@ -247,6 +256,40 @@ def insert_draft_sequences
   SQL
 end
 
+def insert_automatic_group_users
+  Group::AUTO_GROUPS.each do |group_name, group_id|
+    user_condition =
+      case group_name
+      when :everyone
+        "TRUE"
+      when :admins
+        "id > 0 AND admin AND NOT staged"
+      when :moderators
+        "id > 0 AND moderator AND NOT staged"
+      when :staff
+        "id > 0 AND (moderator OR admin) AND NOT staged"
+      when :trust_level_1, :trust_level_2, :trust_level_3, :trust_level_4
+        "id > 0 AND trust_level >= :min_trust_level AND NOT staged"
+      when :trust_level_0
+        "id > 0 AND NOT staged"
+      end
+
+    DB.exec(<<~SQL, group_id: group_id, min_trust_level: group_id - 10)
+      INSERT INTO group_users (group_id, user_id, created_at, updated_at)
+      SELECT :group_id, id, NOW(), NOW()
+        FROM users u
+       WHERE #{user_condition}
+         AND NOT EXISTS (
+                          SELECT 1
+                            FROM group_users gu
+                           WHERE gu.group_id = :group_id AND gu.user_id = u.id
+                        )
+    SQL
+
+    Group.reset_user_count(Group.find(group_id))
+  end
+end
+
 def update_user_stats
   log "Updating user stats..."
 
@@ -404,9 +447,9 @@ def update_users
       GROUP BY p.user_id
     )
     UPDATE users
-       SET first_seen_at  = X.min_created_at
+       SET first_seen_at  = LEAST(first_seen_at, X.min_created_at)
-         , last_seen_at   = X.max_created_at
+         , last_seen_at   = GREATEST(last_seen_at, X.max_created_at)
-         , last_posted_at = X.max_created_at
+         , last_posted_at = GREATEST(last_posted_at, X.max_created_at)
       FROM X
      WHERE id = X.user_id
        AND (COALESCE(first_seen_at, '1970-01-01')  <> X.min_created_at
@@ -459,9 +502,15 @@ def update_topic_users
   SQL
 end
 
+def update_topic_featured_users
+  log "Updating topic featured users..."
+  TopicFeaturedUsers.ensure_consistency!
+end
+
 def create_category_definitions
   log "Creating category definitions"
   Category.ensure_consistency!
+  Site.clear_cache
 end
 
 def log(message)
@@ -654,3 +703,80 @@ task "import:update_avatars_from_sso" => :environment do
   status_queue.close
   status_thread.join
 end
+
+def run_jobs
+  log "Running jobs"
+
+  Jobs::EnsureDbConsistency.new.execute({})
+  Jobs::DirectoryRefreshOlder.new.execute({})
+  Jobs::DirectoryRefreshDaily.new.execute({})
+  Jobs::ReindexSearch.new.execute({})
+  Jobs::TopRefreshToday.new.execute({})
+  Jobs::TopRefreshOlder.new.execute({})
+  Jobs::Weekly.new.execute({})
+end
+
+desc "Rebake posts that contain polls"
+task "import:rebake_uncooked_posts_with_polls" => :environment do
+  log "Rebaking posts with polls"
+
+  Jobs.run_immediately!
+
+  posts =
+    Post.where("EXISTS (SELECT 1 FROM polls WHERE polls.post_id = posts.id)").where(
+      "baked_version <> ? or baked_version IS NULL",
+      Post::BAKED_VERSION,
+    )
+
+  max_count = posts.count
+  current_count = 0
+
+  posts.find_each(order: :desc) do |post|
+    post.rebake!
+    current_count += 1
+    print "\r%7d / %7d" % [current_count, max_count]
+  end
+end
+
+desc "Rebake posts that contain events"
+task "import:rebake_uncooked_posts_with_events" => :environment do
+  log "Rebaking posts with events"
+
+  Jobs.run_immediately!
+
+  posts =
+    Post.where(
+      "EXISTS (SELECT 1 FROM discourse_post_event_events WHERE discourse_post_event_events.id = posts.id)",
+    ).where("baked_version <> ? or baked_version IS NULL", Post::BAKED_VERSION)
+
+  max_count = posts.count
+  current_count = 0
+
+  posts.find_each(order: :desc) do |post|
+    post.rebake!
+    current_count += 1
+    print "\r%7d / %7d" % [current_count, max_count]
+  end
+end
+
+desc "Rebake posts that have tag"
+task "import:rebake_uncooked_posts_with_tag", [:tag_name] => :environment do |_task, args|
+  log "Rebaking posts with tag"
+
+  Jobs.run_immediately!
+
+  posts =
+    Post.where(
+      "EXISTS (SELECT 1 FROM topic_tags JOIN tags ON tags.id = topic_tags.tag_id WHERE topic_tags.topic_id = posts.topic_id AND tags.name = ?)",
+      args[:tag_name],
+    ).where("baked_version <> ? or baked_version IS NULL", Post::BAKED_VERSION)
+
+  max_count = posts.count
+  current_count = 0
+
+  posts.find_each(order: :desc) do |post|
+    post.rebake!
+    current_count += 1
+    print "\r%7d / %7d" % [current_count, max_count]
+  end
+end