"""TaskConfig for MCP SEP-1686 background task execution modes.

This module defines the configuration for how tools, resources, and prompts
handle task-augmented execution as specified in SEP-1686.
"""

from __future__ import annotations

import functools
import inspect
from collections.abc import Callable
from dataclasses import dataclass
from datetime import timedelta
from typing import Any, Literal

from fastmcp.utilities.async_utils import is_coroutine_function

# Task execution modes per SEP-1686 / MCP ToolExecution.taskSupport
TaskMode = Literal["forbidden", "optional", "required"]

# Default values for task metadata (single source of truth)
DEFAULT_POLL_INTERVAL = timedelta(seconds=5)  # Default poll interval
DEFAULT_POLL_INTERVAL_MS = int(DEFAULT_POLL_INTERVAL.total_seconds() * 1000)
DEFAULT_TTL_MS = 60_000  # Default TTL in milliseconds


@dataclass
class TaskMeta:
    """Metadata for task-augmented execution requests.

    When passed to call_tool/read_resource/get_prompt, signals that
    the operation should be submitted as a background task.

    Attributes:
        ttl: Client-requested TTL in milliseconds. If None, uses server default.
        fn_key: Docket routing key. Auto-derived from component name if None.
    """

    ttl: int | None = None
    fn_key: str | None = None


@dataclass
class TaskConfig:
    """Configuration for MCP background task execution (SEP-1686).

    Controls how a component handles task-augmented requests:

    - "forbidden": Component does not support task execution. Clients must not
      request task augmentation; server returns -32601 if they do.
    - "optional": Component supports both synchronous and task execution.
      Client may request task augmentation or call normally.
    - "required": Component requires task execution. Clients must request task
      augmentation; server returns -32601 if they don't.

    Important:
        Task-enabled components must be available at server startup to be
        registered with all Docket workers. Components added dynamically after
        startup will not be registered for background execution.

    Example:
        ```python
        from fastmcp import FastMCP
        from fastmcp.server.tasks import TaskConfig

        mcp = FastMCP("MyServer")

        # Background execution required
        @mcp.tool(task=TaskConfig(mode="required"))
        async def long_running_task(): ...

        # Supports both modes (default when task=True)
        @mcp.tool(task=TaskConfig(mode="optional"))
        async def flexible_task(): ...
        ```
    """

    mode: TaskMode = "optional"
    poll_interval: timedelta = DEFAULT_POLL_INTERVAL

    @classmethod
    def from_bool(cls, value: bool) -> TaskConfig:
        """Convert boolean task flag to TaskConfig.

        Args:
            value: True for "optional" mode, False for "forbidden" mode.

        Returns:
            TaskConfig with appropriate mode.
        """
        return cls(mode="optional" if value else "forbidden")

    def supports_tasks(self) -> bool:
        """Check if this component supports task execution.

        Returns:
            True if mode is "optional" or "required", False if "forbidden".
        """
        return self.mode != "forbidden"

    def validate_function(self, fn: Callable[..., Any], name: str) -> None:
        """Validate that function is compatible with this task config.

        Task execution requires:
        1. fastmcp[tasks] to be installed (pydocket)
        2. Async functions

        Raises ImportError if mode is "optional" or "required" but pydocket
        is not installed. Raises ValueError if function is synchronous.

        Args:
            fn: The function to validate (handles callable classes and staticmethods).
            name: Name for error messages.

        Raises:
            ImportError: If task execution is enabled but pydocket not installed.
            ValueError: If task execution is enabled but function is sync.
        """
        if not self.supports_tasks():
            return

        # Check that docket is available for task execution
        # Lazy import to avoid circular: dependencies.py → http.py → tasks/__init__.py → config.py
        from fastmcp.server.dependencies import require_docket

        require_docket(f"`task=True` on function '{name}'")

        # Unwrap callable classes and staticmethods
        fn_to_check = fn
        if (
            not inspect.isroutine(fn)
            and not isinstance(fn, functools.partial)
            and callable(fn)
        ):
            fn_to_check = fn.__call__
        if isinstance(fn_to_check, staticmethod):
            fn_to_check = fn_to_check.__func__

        if not is_coroutine_function(fn_to_check):
            raise ValueError(
                f"'{name}' uses a sync function but has task execution enabled. "
                "Background tasks require async functions."
            )

        # Note: Context IS now available in background task workers (SEP-1686)
        # The wiring in _CurrentContext creates a task-aware Context with task_id
        # and session from the registry. No warning needed.
