"""Task state management.

Tracks long-running tasks (e.g. graph build) so callers can poll progress.
"""

import uuid
import threading
from datetime import datetime
from enum import Enum
from typing import Dict, Any, Optional
from dataclasses import dataclass, field

from ..utils.locale import t


class TaskStatus(str, Enum):
    """Task status enum."""
    PENDING = "pending"          # waiting
    PROCESSING = "processing"    # in progress
    COMPLETED = "completed"      # finished successfully
    FAILED = "failed"            # finished with error


@dataclass
class Task:
    """Task data class."""
    task_id: str
    task_type: str
    status: TaskStatus
    created_at: datetime
    updated_at: datetime
    progress: int = 0              # overall progress percentage 0-100
    message: str = ""              # human-readable status message
    result: Optional[Dict] = None  # task result payload
    error: Optional[str] = None    # error message when failed
    metadata: Dict = field(default_factory=dict)  # arbitrary caller metadata
    progress_detail: Dict = field(default_factory=dict)  # fine-grained progress info

    def to_dict(self) -> Dict[str, Any]:
        """Serialize the task to a JSON-friendly dict."""
        return {
            "task_id": self.task_id,
            "task_type": self.task_type,
            "status": self.status.value,
            "created_at": self.created_at.isoformat(),
            "updated_at": self.updated_at.isoformat(),
            "progress": self.progress,
            "message": self.message,
            "progress_detail": self.progress_detail,
            "result": self.result,
            "error": self.error,
            "metadata": self.metadata,
        }


class TaskManager:
    """Thread-safe singleton task registry."""

    _instance = None
    _lock = threading.Lock()

    def __new__(cls):
        if cls._instance is None:
            with cls._lock:
                if cls._instance is None:
                    cls._instance = super().__new__(cls)
                    cls._instance._tasks: Dict[str, Task] = {}
                    cls._instance._task_lock = threading.Lock()
        return cls._instance

    def create_task(self, task_type: str, metadata: Optional[Dict] = None) -> str:
        """Create a new task.

        Args:
            task_type: Task type identifier.
            metadata: Optional caller-supplied metadata.

        Returns:
            The newly created task id.
        """
        task_id = str(uuid.uuid4())
        now = datetime.now()

        task = Task(
            task_id=task_id,
            task_type=task_type,
            status=TaskStatus.PENDING,
            created_at=now,
            updated_at=now,
            metadata=metadata or {}
        )

        with self._task_lock:
            self._tasks[task_id] = task

        return task_id

    def get_task(self, task_id: str) -> Optional[Task]:
        """Return the task for ``task_id`` or ``None`` if unknown."""
        with self._task_lock:
            return self._tasks.get(task_id)

    def update_task(
        self,
        task_id: str,
        status: Optional[TaskStatus] = None,
        progress: Optional[int] = None,
        message: Optional[str] = None,
        result: Optional[Dict] = None,
        error: Optional[str] = None,
        progress_detail: Optional[Dict] = None
    ):
        """Update mutable fields on an existing task.

        Args:
            task_id: Task id to update.
            status: New status, if changing.
            progress: New overall progress (0-100), if changing.
            message: New status message, if changing.
            result: New result payload, if changing.
            error: New error message, if changing.
            progress_detail: New fine-grained progress info, if changing.
        """
        with self._task_lock:
            task = self._tasks.get(task_id)
            if task:
                task.updated_at = datetime.now()
                if status is not None:
                    task.status = status
                if progress is not None:
                    task.progress = progress
                if message is not None:
                    task.message = message
                if result is not None:
                    task.result = result
                if error is not None:
                    task.error = error
                if progress_detail is not None:
                    task.progress_detail = progress_detail

    def complete_task(self, task_id: str, result: Dict):
        """Mark a task as completed and attach the result."""
        self.update_task(
            task_id,
            status=TaskStatus.COMPLETED,
            progress=100,
            message=t('progress.taskComplete'),
            result=result
        )

    def fail_task(self, task_id: str, error: str):
        """Mark a task as failed and attach the error message."""
        self.update_task(
            task_id,
            status=TaskStatus.FAILED,
            message=t('progress.taskFailed'),
            error=error
        )

    def list_tasks(self, task_type: Optional[str] = None) -> list:
        """List tasks, optionally filtered by ``task_type``, newest first."""
        with self._task_lock:
            tasks = list(self._tasks.values())
            if task_type:
                tasks = [t for t in tasks if t.task_type == task_type]
            return [t.to_dict() for t in sorted(tasks, key=lambda x: x.created_at, reverse=True)]

    def cleanup_old_tasks(self, max_age_hours: int = 24):
        """Drop completed/failed tasks older than ``max_age_hours``."""
        from datetime import timedelta
        cutoff = datetime.now() - timedelta(hours=max_age_hours)

        with self._task_lock:
            old_ids = [
                tid for tid, task in self._tasks.items()
                if task.created_at < cutoff and task.status in [TaskStatus.COMPLETED, TaskStatus.FAILED]
            ]
            for tid in old_ids:
                del self._tasks[tid]