Add UserActivities module for structured user activity history

This commit:
- Adds UserActivities module to fetch and organize user activities
- Implements efficient SQL queries with Common Table Expressions (CTEs)
- Groups activities hierarchically by day and then by activity type
- Supports pagination with limit and offset parameters

lib/user_activities.rb

@@ -0,0 +1,194 @@
+# rubocop:disable Metrics/ModuleLength
+module UserActivities
+  def self.for_user(user_id, limit: 5, offset: 0)
+    ActiveRecord::Base.connection.execute(activity_sql(user_id, :limit => limit, :offset => offset)).to_a
+  end
+
+  def self.count_activities(user_id)
+    ActiveRecord::Base.connection.execute(count_sql(user_id)).first["count"]
+  end
+
+  private_class_method def self.count_sql(user_id)
+    <<~SQL.squish
+      WITH activities AS (
+        #{base_activities_sql(user_id)}
+      )
+      SELECT COUNT(DISTINCT DATE_TRUNC('day', timestamp)) as count
+      FROM activities
+    SQL
+  end
+
+  private_class_method def self.activity_sql(user_id, limit:, offset:)
+    <<~SQL.squish
+      WITH activities AS (
+        #{base_activities_sql(user_id)}
+      ),
+      activity_days AS (
+        SELECT DISTINCT DATE_TRUNC('day', timestamp) as day
+        FROM activities
+        ORDER BY day DESC
+        LIMIT #{limit}
+        OFFSET #{offset}
+      ),
+      activities_by_day AS (
+        SELECT
+          DATE_TRUNC('day', a.timestamp) AS activity_date,
+          a.category,
+          a.activity_type,
+          COUNT(*) as count,
+          JSONB_AGG(
+            JSONB_BUILD_OBJECT(
+              'id', a.activity_id,
+              'reference_id', a.reference_id,
+              'additional_reference_id', a.additional_reference_id,
+              'description', a.description,
+              'source_type', a.source_type,
+              'user_display_name', a.user_display_name,
+              'timestamp', a.timestamp
+            )
+            ORDER BY a.timestamp DESC
+          ) as items
+        FROM activities a
+        INNER JOIN activity_days d ON DATE_TRUNC('day', a.timestamp) = d.day
+        GROUP BY activity_date, a.category, a.activity_type
+      ),
+      grouped_activities AS (
+        SELECT
+          activity_date,
+          JSONB_OBJECT_AGG(
+            CONCAT(category, ':', activity_type),
+            JSONB_BUILD_OBJECT(
+              'count', count,
+              'items', items
+            )
+          ) as activity_groups
+        FROM activities_by_day
+        GROUP BY activity_date
+        ORDER BY activity_date DESC
+      )
+      SELECT * FROM grouped_activities
+    SQL
+  end
+
+  # Extract common activity types
+  private_class_method def self.base_activities_sql(user_id)
+    quoted_user_id = ActiveRecord::Base.connection.quote(user_id)
+    [
+      changeset_sql(quoted_user_id),
+      diary_entry_sql(quoted_user_id),
+      changeset_comment_sql(quoted_user_id),
+      note_comment_sql(quoted_user_id),
+      diary_comment_sql(quoted_user_id),
+      gpx_file_sql(quoted_user_id)
+    ].join(" UNION ALL ")
+  end
+
+  private_class_method def self.changeset_sql(quoted_user_id)
+    <<~SQL.squish
+      SELECT
+        c.created_at AS timestamp,
+        CAST('changeset' AS text) AS category,
+        CAST('opened' AS text) AS activity_type,
+        c.id AS activity_id,
+        c.id AS reference_id,
+        NULL AS additional_reference_id,
+        NULL AS description,
+        'changeset' AS source_type,
+        NULL AS user_display_name
+      FROM changesets c
+      WHERE c.user_id = #{quoted_user_id}
+    SQL
+  end
+
+  private_class_method def self.diary_entry_sql(quoted_user_id)
+    <<~SQL.squish
+      SELECT
+        d.created_at AS timestamp,
+        CAST('diary' AS text) AS category,
+        CAST('diary_entry' AS text) AS activity_type,
+        d.id AS activity_id,
+        d.id AS reference_id,
+        d.title AS additional_reference_id,
+        d.body AS description,
+        'diary' AS source_type,
+        u.display_name AS user_display_name
+      FROM diary_entries d
+      JOIN users u ON u.id = #{quoted_user_id}
+      WHERE d.user_id = #{quoted_user_id}
+      AND d.visible = true
+    SQL
+  end
+
+  private_class_method def self.changeset_comment_sql(quoted_user_id)
+    <<~SQL.squish
+      SELECT
+        cc.created_at,
+        CAST('comment' AS text) AS category,
+        CAST('comment' AS text) AS activity_type,
+        cc.id,
+        cc.changeset_id AS reference_id,
+        NULL AS additional_reference_id,
+        cc.body,
+        'changeset' AS source_type,
+        NULL AS user_display_name
+      FROM changeset_comments cc
+      WHERE cc.author_id = #{quoted_user_id}
+    SQL
+  end
+
+  private_class_method def self.note_comment_sql(quoted_user_id)
+    <<~SQL.squish
+      SELECT
+        nc.created_at,
+        CAST('comment' AS text) AS category,
+        CAST('comment' AS text) AS activity_type,
+        nc.id,
+        nc.note_id AS reference_id,
+        NULL AS additional_reference_id,
+        nc.body,
+        'note' AS source_type,
+        NULL AS user_display_name
+      FROM note_comments nc
+      WHERE nc.author_id = #{quoted_user_id}
+    SQL
+  end
+
+  private_class_method def self.diary_comment_sql(quoted_user_id)
+    <<~SQL.squish
+      SELECT
+        dc.created_at,
+        CAST('comment' AS text) AS category,
+        CAST('comment' AS text) AS activity_type,
+        dc.id,
+        dc.diary_entry_id AS reference_id,
+        d.title AS additional_reference_id,
+        dc.body,
+        'diary' AS source_type,
+        u.display_name AS user_display_name
+      FROM diary_comments dc
+      JOIN diary_entries d ON d.id = dc.diary_entry_id
+      JOIN users u ON u.id = #{quoted_user_id}
+      WHERE dc.user_id = #{quoted_user_id}
+      AND dc.visible = true
+    SQL
+  end
+
+  private_class_method def self.gpx_file_sql(quoted_user_id)
+    <<~SQL.squish
+      SELECT
+        g.timestamp AS timestamp,
+        CAST('gpx' AS text) AS category,
+        CAST('upload' AS text) AS activity_type,
+        g.id AS activity_id,
+        g.id AS reference_id,
+        g.name AS additional_reference_id,
+        g.description AS description,
+        'gpx' AS source_type,
+        u.display_name AS user_display_name
+      FROM gpx_files g
+      JOIN users u ON u.id = #{quoted_user_id}
+      WHERE g.user_id = #{quoted_user_id}
+    SQL
+  end
+end
+# rubocop:enable Metrics/ModuleLength