refactor(thread-move): wip implement thread move db query function, c…

…ontinued, add comments more queries in transaction

lib/epochtalk_server/models/thread.ex

@@ -250,6 +250,7 @@ defmodule EpochtalkServer.Models.Thread do
           {:ok, thread :: t()} | {:error, Ecto.Changeset.t()}
   def move(thread_id, board_id) do
     case Repo.transaction(fn ->
+      # query and lock thread for update
       thread_lock_query =
        from t in Thread,
          join: mt in MetadataThread,
@@ -258,9 +259,13 @@ defmodule EpochtalkServer.Models.Thread do
          select: {t, mt},
          lock: "FOR UPDATE"
 
+      # locked thread, reference this when updating
       {thread, _thread_meta} = Repo.one(thread_lock_query)
 
+      # prevent moving board to same board
       if thread.board_id != board_id do
+
+        # query old board and lock for update
         old_board_lock_query =
          from b in Board,
            join: mb in MetadataBoard,
@@ -269,8 +274,40 @@ defmodule EpochtalkServer.Models.Thread do
            select: {b, mb},
            lock: "FOR UPDATE"
 
+        # locked old_board, reference this when updating
         {old_board, _old_board_meta} = Repo.one(old_board_lock_query)
 
+        # query new board and lock for update
+        new_board_lock_query =
+          from b in Board,
+            join: mb in MetadataBoard,
+            on: mb.board_id == b.id,
+            where: b.id == ^board_id,
+            select: {b, mb},
+            lock: "FOR UPDATE"
+
+        # locked new_board, reference this when updating
+        {new_board, _new_board_meta} = Repo.one(new_board_lock_query)
+
+        # update old_board, thread and post count
+        old_board_updated =
+          old_board
+          |> change([thread_count: old_board.thread_count-1, post_count: old_board.post_count-1])
+          |> Repo.update!()
+
+        # update new_board, thread and post count
+        new_board_updated =
+          new_board
+          |> change([thread_count: new_board.thread_count+1, post_count: new_board.post_count+1])
+          |> Repo.update!()
+
+        # update thread's original board_id with new_board's id
+        thread_updated =
+          thread
+          |> change(board_id: new_board.id)
+          |> Repo.update!()
+
+        %{old_board_name: old_board.name, old_board_id: old_board.id}
       else
         {:error, :invalid_board_id}
       end