Support random check out different snapshot

api/operation.py

@@ -74,3 +74,79 @@ def execute_redo(name: str) -> None:
 
     _execute(name, redo)
     _update_current_operation(name, curr, child)
+
+# snapshot support to check out between different version of database
+# snapshot is persistent
+# since redo always remember the recently undo path
+
+def take_snapshot(name: str, tag: str) -> None:
+    if tag == None or tag == '':
+        print('Non empty tag is expected!')
+        return
+
+    curr = _get_current_operation(name)
+
+    with conn[name].cursor() as cur:
+        parent = _get_current_operation(name)
+        cur.execute(f"insert into snapshot_operation (id, tag) values ({curr}, '{tag}')")
+
+
+def _get_parents(name: str, id: int) -> list[int]:
+    ids = [id]
+    with conn[name].cursor(row_factory=dict_row) as cur:
+        while ids[-1] != 0:
+            cur.execute(f"select parent from operation where id = {ids[-1]}")
+            ids.append(int(cur.fetchone()['parent']))
+    return ids
+
+def pick_snapshot(name: str, tag: str) -> None:
+    if tag == None or tag == '':
+        print('Non empty tag is expected!')
+        return
+
+    curr = _get_current_operation(name)
+    curr_parents = _get_parents(name, curr)
+
+    with conn[name].cursor(row_factory=dict_row) as cur:
+        cur.execute(f"select id from snapshot_operation where tag = '{tag}'")
+        if cur.rowcount < 1:
+            print('No such snapshot!')
+            return
+        target = int(cur.fetchone()['id'])
+        if target in curr_parents: # target -> curr
+            for i in range(curr_parents.index(target)):
+                execute_undo(name)
+        else:
+            target_parents = _get_parents(name, target)
+            if curr in target_parents: # curr -> target
+                for i in range(target_parents.index(curr)):
+                    execute_redo(name)
+            else:
+                ancestor_index = -1
+                while curr_parents[ancestor_index] == target_parents[ancestor_index]:
+                    ancestor_index -= 1
+
+                # ancestor -> curr
+                ancestor = curr_parents[ancestor_index + 1] # ancestor_index + 1 is common parent
+                for i in range(curr_parents.index(ancestor)):
+                    execute_undo(name)
+                # ancestor -> redo, need assign redo_child
+                while target_parents[ancestor_index] != target:
+                    cur.execute(f"update operation set redo_child = '{target_parents[ancestor_index]}' where id = '{target_parents[ancestor_index + 1]}'")
+                    execute_redo(name)
+                    ancestor_index -= 1
+                cur.execute(f"update operation set redo_child = '{target}' where id = '{target_parents[1]}'")
+                execute_redo(name)
+
+# transaction is volatile, commit/rollback will destroy transaction.
+# can not undo a committed transaction or redo a rollback transaction.
+# it may remove snapshot tag if snapshot in a rollback transaction
+
+def start_transaction(name: str) -> None:
+    pass
+
+def commit_transaction(name: str) -> None:
+    pass
+
+def rollback_transaction(name: str) -> None:
+    pass