Implement undo in by PL/pgSQL

script/script/api/create/1.title.sql

@@ -1,22 +1,27 @@
 -- get_title()
-create function get_title() returns text as
+create function tj.get_title() returns text as
 $$
-    select value from title;
-$$ language sql;
+declare
+    title text;
+begin
+    select value into title from tj.title;
+    return title;
+end;
+$$ language plpgsql;
 
 -- update_title()
-create function update_title(new_title text) returns void as
+create function tj.set_title(new_title text) returns void as
 $$
 declare
     old_title text;
     redo text;
     undo text;
 begin
-    select get_title() into old_title;
-    update title set value = new_title where value = old_title;
+    select tj.get_title() into old_title;
+    update tj.title set value = new_title where value = old_title;
 
-    redo := concat('update title set value = ''', new_title, ''' where value = ''', old_title, '''');
-    undo := concat('update title set value = ''', old_title, ''' where value = ''', new_title, '''');
-    insert into operation values (default, redo, undo);
+    redo := concat('update tj.title set value = ''', new_title, ''' where value = ''', old_title, '''');
+    undo := concat('update tj.title set value = ''', old_title, ''' where value = ''', new_title, '''');
+    perform tj.add_operation(redo, undo);
 end;
 $$ language plpgsql;

script/script/api/create/operation.sql

@@ -0,0 +1,87 @@
+create function tj.add_operation(redo text, undo text) returns void as
+$$
+declare
+    parent_id int;
+    curr_id int;
+begin
+    select id into parent_id from tj.current_operation;
+    insert into tj.operation (id, redo, undo, parent) values (default, redo, undo, parent_id);
+    select max(id) into curr_id from tj.operation;
+    update tj.current_operation set id = curr_id where id = parent_id;
+end;
+$$ language plpgsql;
+
+create function tj.have_transaction() returns boolean as
+$$
+declare
+    tran_count int;
+begin
+    select count(*) into tran_count from tj.transaction_operation;
+    return tran_count > 0;
+end;
+$$ language plpgsql;
+
+create function tj.execute_undo(discard boolean) returns void as
+$$
+declare
+    curr_id int;
+    have_tran boolean;
+    tran_id int;
+    strict_mode boolean;
+    undo_sql text;
+    parent_id int;
+begin
+    select id into curr_id from tj.current_operation;
+
+    select tj.have_transaction() into have_tran;
+    if have_tran then
+        select strict into strict_mode from tj.transaction_operation;
+        if strict_mode then
+            return; -- strict mode disallow undo
+        else
+            select id into tran_id from tj.transaction_operation;
+            if tran_id >= curr_id then
+                return; -- # normal mode disallow undo start point, and there is foreign key constraint
+            end if;
+        end if;
+    end if;
+
+    select undo into undo_sql from tj.operation where id = curr_id;
+    if undo_sql = '' then
+        return;
+    end if;
+
+    select parent into parent_id from tj.operation where id = curr_id;
+    if discard then
+        update tj.operation set redo_child = null where id = parent_id;
+    else
+        update tj.operation set redo_child = curr_id where id = parent_id;
+    end if;
+
+    execute undo_sql;
+
+    update tj.current_operation set id = parent_id where id = curr_id;
+
+    if discard then
+        delete from tj.transaction_operation where id = curr_id;
+        delete from tj.snapshot_operation where id = curr_id;
+        delete from tj.operation where id = curr_id;
+    end if;
+end;
+$$ language plpgsql;
+
+create function tj.undo() returns void as
+$$
+declare
+begin
+    perform tj.execute_undo(false);
+end;
+$$ language plpgsql;
+
+create function tj.discard_undo() returns void as
+$$
+declare
+begin
+    perform tj.execute_undo(true);
+end;
+$$ language plpgsql;

script/script/api/create/project.sql

@@ -0,0 +1,9 @@
+create function tj.have_project(in_name text) returns boolean as
+$$
+declare
+    db_count int;
+begin
+    select count(*) into db_count from pg_database where datname = in_name;
+    return db_count > 0;
+end;
+$$ language plpgsql;

script/script/api/drop/1.title.sql

@@ -0,0 +1,3 @@
+drop function if exists tj.set_title;
+
+drop function if exists tj.get_title;

script/script/api/drop/operation.sql

@@ -0,0 +1,7 @@
+drop function if exists tj.discard_undo;
+drop function if exists tj.undo;
+drop function if exists tj.execute_undo;
+
+drop function if exists tj.have_transaction;
+
+drop function if exists tj.add_operation;

script/script/api/plpgsql.sql

@@ -0,0 +1,6 @@
+create function xxx() returns void as
+$$
+declare
+begin
+end;
+$$ language plpgsql;

script/script/template.py

@@ -31,10 +31,14 @@ sql_create = [
     "table/create/26.labels.sql",
     "table/create/27.backdrop.sql",
     "table/create/28.end.sql",
-    "table/create/operation.sql"
+    "table/create/operation.sql",
+    "api/create/operation.sql",
+    "api/create/1.title.sql"
 ]
 
 sql_drop = [
+    "api/drop/1.title.sql",
+    "api/drop/operation.sql",
     "table/drop/operation.sql",
     "table/drop/28.end.sql",
     "table/drop/27.backdrop.sql",