created commands data structure (#16)

* created decision data struture

* added enum for command types

* formatting

* better command names

* updated function names

modules/decision_command.py

@@ -0,0 +1,56 @@
+"""
+Command data structure used by decision module.
+"""
+
+import enum
+
+
+class DecisionCommand:
+    """
+    Contains command to send to drone.
+
+    The following are valid command constructors:
+
+    * DecisionCommand.create_stop_command
+    * DecisionCommand.create_resume_command
+    """
+
+    __create_key = object()
+
+    class CommandType(enum.Enum):
+        """
+        Valid commands.
+        """
+
+        STOP_MISSION_AND_HALT = 0
+        RESUME_MISSION = 1
+
+    @classmethod
+    def create_stop_mission_and_halt_command(cls) -> "tuple[bool, DecisionCommand | None]":
+        """
+        Command to stop and loiter the drone.
+        """
+        return True, DecisionCommand(
+            cls.__create_key, DecisionCommand.CommandType.STOP_MISSION_AND_HALT
+        )
+
+    @classmethod
+    def create_resume_mission_command(cls) -> "tuple[bool, DecisionCommand | None]":
+        """
+        Command to resume auto mission.
+        """
+        return True, DecisionCommand(cls.__create_key, DecisionCommand.CommandType.RESUME_MISSION)
+
+    def __init__(self, create_key: object, command: CommandType) -> None:
+        """
+        Private constructor, use create() method.
+        """
+        assert create_key is DecisionCommand.__create_key, "Use create() method"
+
+        self.command = command
+
+    def __str__(self) -> str:
+        """
+        String representation
+        """
+        return f"{self.__class__.__name__}: {self.command}"