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Dagster/API_R&D/api/task.py

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+from abc import ABC, abstractmethod
+from enum import Enum
+from typing import List, Any, Optional
+
+from api.io_port import InPort, OutPort
+from api.execution_context import ExecutionContext
+
+
+class Status(Enum):
+    PENDING = "pending"
+    READY = "ready"
+    RUNNING = "running"
+    PAUSED = "paused"
+    STOPPED = "stopped"
+    COMPLETED = "completed"
+    FAILED = "failed"
+
+
+class TaskEvent(Enum):
+    BEFORE_RUN = "before_run"
+    AFTER_RUN = "after_run"
+    ON_ERROR = "on_error"
+    STATUS_CHANGED = "status_changed"
+    ON_START = "on_start"
+    ON_FINISH = "on_finish"
+
+
+class TaskEventListener:
+    def handle(self, event: TaskEvent, task: "Task", payload: Optional[Any] = None):
+        pass
+
+
+class Task(ABC):
+    def __init__(self, name: str):
+        self.name = name
+        self.status = Status.PENDING
+
+        self.in_ports: List[InPort] = []
+        self.out_ports: List[OutPort] = []
+
+        self._listeners: List[TaskEventListener] = []
+        self.parent_task: Optional["Task"] = None
+
+    # Event System
+    def add_listener(self, listener: TaskEventListener):
+        self._listeners.append(listener)
+
+    def _emit(self, event: TaskEvent, payload: Optional[Any] = None):
+        for listener in self._listeners:
+            listener.handle(event, self, payload)
+
+    def _set_status(self, new_status: Status):
+        old_status = self.status
+        self.status = new_status
+
+        if old_status != new_status:
+            self._emit(TaskEvent.STATUS_CHANGED, {"from": old_status, "to": new_status})
+
+    # Input Readiness Check
+    def check_inputs_ready(self, context: ExecutionContext) -> bool:
+        for port in self.in_ports:
+            if not port.is_ready(context):
+                return False
+        return True
+
+    # Execution Wrapper
+    def run(self, context: ExecutionContext):
+        """
+        Base Task.run() SHOULD NOT be used for Module.
+        Module overrides run() completely.
+        """
+        raise NotImplementedError(
+            "Task.run() should not be called for Module. Use Module.run() instead."
+        )
+
+    @abstractmethod
+    def execute(self, context: ExecutionContext):
+        pass