Initial work on a full backup option

Creates the Backup command and a general serializer.

pfbudget/common/types.py

@@ -51,6 +51,12 @@ class Operation(Enum):
     ImportCategoryGroups = auto()
 
 
+class ExportFormat(Enum):
+    CSV = auto()
+    JSON = auto()
+    pickle = auto()
+
+
 class TransactionError(Exception):
     pass
 

pfbudget/core/command.py

@@ -0,0 +1,40 @@
+from abc import ABC, abstractmethod
+import csv
+import json
+from pathlib import Path
+import pickle
+from typing import Any, Type
+
+from pfbudget.common.types import ExportFormat
+from pfbudget.db.client import Client
+from pfbudget.utils.serializer import serialize
+
+
+class Command(ABC):
+    @abstractmethod
+    def execute(self) -> None:
+        raise NotImplementedError
+
+    def undo(self) -> None:
+        raise NotImplementedError
+
+
+class ExportCommand(Command):
+    def __init__(self, client: Client, what: Type[Any], fn: Path, format: ExportFormat):
+        self.__client = client
+        self.what = what
+        self.fn = fn
+        self.format = format
+
+    def execute(self) -> None:
+        values = self.__client.select(self.what)
+        match self.format:
+            case ExportFormat.CSV:
+                with open(self.fn, "w", newline="") as f:
+                    csv.writer(f).writerows([serialize(e) for e in values])
+            case ExportFormat.JSON:
+                with open(self.fn, "w", newline="") as f:
+                    json.dump([serialize(e) for e in values], f, indent=4, default=str)
+            case ExportFormat.pickle:
+                with open(self.fn, "wb") as f:
+                    pickle.dump([serialize(e) for e in values], f)

pfbudget/utils/serializer.py

@@ -0,0 +1,21 @@
+from collections.abc import Mapping
+from dataclasses import fields
+from functools import singledispatch
+from typing import Any
+
+from pfbudget.db.model import Transaction, TransactionCategory
+
+
+@singledispatch
+def serialize(obj: Any) -> Mapping[str, Any]:
+    raise NotImplementedError
+
+
+@serialize.register
+def _(obj: Transaction) -> Mapping[str, Any]:
+    return dict((field.name, getattr(obj, field.name)) for field in fields(obj))
+
+
+@serialize.register
+def _(obj: TransactionCategory) -> Mapping[str, Any]:
+    return dict((field.name, getattr(obj, field.name)) for field in fields(obj))