"""Task backend abstraction for Tasks TUI.

This module defines the abstract interface that all task backends must implement,
allowing the TUI to work with different task management systems (dstask, taskwarrior, etc.)
"""

from abc import ABC, abstractmethod
from dataclasses import dataclass, field
from datetime import datetime, timezone
from enum import Enum
from typing import Optional


class TaskStatus(Enum):
    """Task status values."""

    PENDING = "pending"
    ACTIVE = "active"
    DONE = "done"
    DELETED = "deleted"


class TaskPriority(Enum):
    """Task priority levels (P0 = highest, P3 = lowest)."""

    P0 = "P0"  # Critical
    P1 = "P1"  # High
    P2 = "P2"  # Normal
    P3 = "P3"  # Low

    @classmethod
    def from_string(cls, value: str) -> "TaskPriority":
        """Parse priority from string."""
        value = value.upper().strip()
        if value in ("P0", "0", "CRITICAL"):
            return cls.P0
        elif value in ("P1", "1", "HIGH", "H"):
            return cls.P1
        elif value in ("P2", "2", "NORMAL", "MEDIUM", "M"):
            return cls.P2
        elif value in ("P3", "3", "LOW", "L"):
            return cls.P3
        return cls.P2  # Default to normal


@dataclass
class Task:
    """Unified task representation across backends."""

    uuid: str
    id: int  # Short numeric ID for display
    summary: str
    status: TaskStatus = TaskStatus.PENDING
    priority: TaskPriority = TaskPriority.P2
    project: str = ""
    tags: list[str] = field(default_factory=list)
    notes: str = ""
    due: Optional[datetime] = None
    created: Optional[datetime] = None
    resolved: Optional[datetime] = None

    @property
    def is_overdue(self) -> bool:
        """Check if task is overdue."""
        if self.due is None or self.status == TaskStatus.DONE:
            return False
        # Use timezone-aware now() if due date is timezone-aware
        now = datetime.now(timezone.utc) if self.due.tzinfo else datetime.now()
        return now > self.due


@dataclass
class Project:
    """Project information."""

    name: str
    task_count: int = 0
    resolved_count: int = 0
    active: bool = True
    priority: TaskPriority = TaskPriority.P2


class TaskBackend(ABC):
    """Abstract base class for task management backends."""

    @abstractmethod
    def get_tasks(
        self,
        project: Optional[str] = None,
        tags: Optional[list[str]] = None,
        status: Optional[TaskStatus] = None,
    ) -> list[Task]:
        """Get tasks, optionally filtered by project, tags, or status.

        Args:
            project: Filter by project name
            tags: Filter by tags (tasks must have all specified tags)
            status: Filter by status

        Returns:
            List of matching tasks
        """
        pass

    @abstractmethod
    def get_next_tasks(self) -> list[Task]:
        """Get the 'next' tasks to work on (priority-sorted actionable tasks)."""
        pass

    @abstractmethod
    def get_task(self, task_id: str) -> Optional[Task]:
        """Get a single task by ID or UUID.

        Args:
            task_id: Task ID (numeric) or UUID

        Returns:
            Task if found, None otherwise
        """
        pass

    @abstractmethod
    def add_task(
        self,
        summary: str,
        project: Optional[str] = None,
        tags: Optional[list[str]] = None,
        priority: Optional[TaskPriority] = None,
        due: Optional[datetime] = None,
        notes: Optional[str] = None,
    ) -> Task:
        """Create a new task.

        Args:
            summary: Task description
            project: Project name
            tags: List of tags
            priority: Task priority
            due: Due date
            notes: Additional notes

        Returns:
            The created task
        """
        pass

    @abstractmethod
    def complete_task(self, task_id: str) -> bool:
        """Mark a task as complete.

        Args:
            task_id: Task ID or UUID

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def delete_task(self, task_id: str) -> bool:
        """Delete a task.

        Args:
            task_id: Task ID or UUID

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def start_task(self, task_id: str) -> bool:
        """Start working on a task (mark as active).

        Args:
            task_id: Task ID or UUID

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def stop_task(self, task_id: str) -> bool:
        """Stop working on a task (mark as pending).

        Args:
            task_id: Task ID or UUID

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def modify_task(
        self,
        task_id: str,
        summary: Optional[str] = None,
        project: Optional[str] = None,
        tags: Optional[list[str]] = None,
        priority: Optional[TaskPriority] = None,
        due: Optional[datetime] = None,
        notes: Optional[str] = None,
    ) -> bool:
        """Modify a task.

        Args:
            task_id: Task ID or UUID
            summary: New summary (if provided)
            project: New project (if provided)
            tags: New tags (if provided)
            priority: New priority (if provided)
            due: New due date (if provided)
            notes: New notes (if provided)

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def get_projects(self) -> list[Project]:
        """Get all projects.

        Returns:
            List of projects with task counts
        """
        pass

    @abstractmethod
    def get_tags(self) -> list[str]:
        """Get all tags.

        Returns:
            List of tag names
        """
        pass

    @abstractmethod
    def sync(self) -> bool:
        """Sync tasks with remote (if supported).

        Returns:
            True if successful (or not applicable)
        """
        pass

    @abstractmethod
    def edit_task_interactive(self, task_id: str) -> bool:
        """Open task in editor for interactive editing.

        Args:
            task_id: Task ID or UUID

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def edit_note_interactive(self, task_id: str) -> bool:
        """Open task notes in editor for interactive editing.

        Args:
            task_id: Task ID or UUID

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def get_context(self) -> Optional[str]:
        """Get the current context filter.

        Returns:
            Current context string, or None if no context is set
        """
        pass

    @abstractmethod
    def set_context(self, context: Optional[str]) -> bool:
        """Set the context filter.

        Args:
            context: Context string (e.g., "+work", "project:foo") or None to clear

        Returns:
            True if successful
        """
        pass

    @abstractmethod
    def get_contexts(self) -> list[str]:
        """Get available predefined contexts.

        For taskwarrior, returns named contexts from config.
        For dstask, may return common tag-based contexts.

        Returns:
            List of context names/filters
        """
        pass