DEV: Improve phpBB3 import script (#15956)

* Optional import of custom user fields from phpBB 3.1+
* Optional import of likes from phpBB3
  Requires the phpBB "Thanks for posts" extension
* Fix import of bookmarks from phpBB3
* Update `created_at` of existing user
* Support mapping of phpBB forums to existing Discourse categories
  This is in addition to the ability of merging phpBB forums and importing into newly created Discourse categories.

script/import_scripts/phpbb3/database/database_3_0.rb

@@ -13,7 +13,7 @@ module ImportScripts::PhpBB3
       SQL
     end
 
-    def fetch_users(last_user_id)
+    def fetch_users(last_user_id, _profile_fields)
       query(<<-SQL, :user_id)
         SELECT u.user_id, u.user_email, u.username, u.user_password, u.user_regdate, u.user_lastvisit, u.user_ip,
           u.user_type, u.user_inactive_reason, g.group_name, b.ban_start, b.ban_end, b.ban_reason,
@@ -227,12 +227,31 @@ module ImportScripts::PhpBB3
         SELECT b.user_id, t.topic_first_post_id
         FROM #{@table_prefix}bookmarks b
           JOIN #{@table_prefix}topics t ON (b.topic_id = t.topic_id)
-        WHERE b.user_id > #{last_user_id}
+        WHERE (b.user_id, b.topic_id) > (#{last_user_id}, #{last_topic_id})
         ORDER BY b.user_id, b.topic_id
         LIMIT #{@batch_size}
       SQL
     end
 
+    def count_likes
+      count(<<-SQL)
+        SELECT COUNT(*) AS count
+        FROM #{@table_prefix}thanks
+        WHERE user_id <> poster_id
+      SQL
+    end
+
+    def fetch_likes(last_post_id, last_user_id)
+      query(<<-SQL, :post_id, :user_id)
+        SELECT post_id, user_id, thanks_time
+        FROM #{@table_prefix}thanks
+        WHERE user_id <> poster_id
+          AND (post_id, user_id) > (#{last_post_id}, #{last_user_id})
+        ORDER BY post_id, user_id
+        LIMIT #{@batch_size}
+      SQL
+    end
+
     def get_smiley(smiley_code)
       query(<<-SQL).first
         SELECT emotion, smiley_url