"""
Core Issue Domain Models

Unified, backend-agnostic issue models that serve as the single source of truth
for all issue tracking operations. These models combine the best features from
various issue tracking systems while maintaining clean domain logic.
"""

from dataclasses import dataclass, field
from datetime import datetime, timezone
from enum import Enum
from typing import List, Optional, Dict, Any
from functools import cached_property


class IssueState(Enum):
    """Universal issue state enumeration with backend mapping support."""
    OPEN = "open"
    CLOSED = "closed"
    IN_PROGRESS = "in_progress"
    BLOCKED = "blocked"

    @classmethod
    def from_string(cls, state_str: str) -> 'IssueState':
        """Convert string to IssueState, with fallback handling."""
        state_map = {
            'open': cls.OPEN,
            'closed': cls.CLOSED,
            'in_progress': cls.IN_PROGRESS,
            'in-progress': cls.IN_PROGRESS,
            'progress': cls.IN_PROGRESS,
            'blocked': cls.BLOCKED,
        }
        return state_map.get(state_str.lower(), cls.OPEN)

    def to_backend_string(self, backend_type: str) -> str:
        """Convert to backend-specific string representation."""
        if backend_type == 'gitea':
            return 'open' if self in [self.OPEN, self.IN_PROGRESS, self.BLOCKED] else 'closed'
        elif backend_type == 'github':
            return self.value
        else:
            return self.value


class Priority(Enum):
    """Universal priority levels."""
    LOW = "low"
    MEDIUM = "medium"
    HIGH = "high"
    CRITICAL = "critical"

    @classmethod
    def from_label(cls, label_name: str) -> Optional['Priority']:
        """Extract priority from label name."""
        if label_name.startswith('priority:'):
            priority_str = label_name.replace('priority:', '')
            try:
                return cls(priority_str)
            except ValueError:
                return None
        return None


class IssueType(Enum):
    """Universal issue types."""
    BUG = "bug"
    FEATURE = "feature"
    ENHANCEMENT = "enhancement"
    TASK = "task"
    DOCUMENTATION = "documentation"
    QUESTION = "question"

    @classmethod
    def from_label(cls, label_name: str) -> Optional['IssueType']:
        """Extract type from label name."""
        try:
            return cls(label_name.lower())
        except ValueError:
            return None


@dataclass(frozen=True)
class Label:
    """Universal label model with backend mapping support."""
    name: str
    color: Optional[str] = None
    description: Optional[str] = None
    backend_id: Optional[str] = None  # Backend-specific ID for sync

    @cached_property
    def category(self) -> str:
        """Categorize label for efficient filtering."""
        if self.name.startswith('priority:'):
            return 'priority'
        elif self.name.startswith('status:'):
            return 'status'
        elif self.name.startswith('type:'):
            return 'type'
        elif self.name in ['bug', 'feature', 'enhancement', 'task', 'documentation', 'question']:
            return 'type'
        else:
            return 'other'

    @cached_property
    def priority(self) -> Optional[Priority]:
        """Extract priority if this is a priority label."""
        return Priority.from_label(self.name)

    @cached_property
    def issue_type(self) -> Optional[IssueType]:
        """Extract issue type if this is a type label."""
        return IssueType.from_label(self.name)


@dataclass(frozen=True)
class LabelCategories:
    """Categorized labels for efficient access."""
    priority_labels: List[Label]
    type_labels: List[Label]
    status_labels: List[Label]
    other_labels: List[Label]

    @cached_property
    def priority(self) -> Optional[Priority]:
        """Get the issue priority."""
        for label in self.priority_labels:
            if label.priority:
                return label.priority
        return None

    @cached_property
    def issue_type(self) -> Optional[IssueType]:
        """Get the issue type."""
        for label in self.type_labels:
            if label.issue_type:
                return label.issue_type
        return None


@dataclass
class User:
    """Universal user model."""
    id: str  # String ID to handle different backend ID types
    username: str
    display_name: Optional[str] = None
    email: Optional[str] = None
    avatar_url: Optional[str] = None
    backend_id: Optional[str] = None  # Backend-specific ID for sync


@dataclass
class Milestone:
    """Universal milestone/project model."""
    id: str
    title: str
    description: Optional[str] = None
    state: str = "open"  # open, closed
    due_date: Optional[datetime] = None
    created_at: Optional[datetime] = None
    updated_at: Optional[datetime] = None
    backend_id: Optional[str] = None


@dataclass
class Comment:
    """Universal comment model."""
    id: str
    body: str
    author: User
    created_at: datetime
    updated_at: Optional[datetime] = None
    backend_id: Optional[str] = None


@dataclass
class Issue:
    """
    Universal Issue model - single source of truth.

    Combines the best features from domain and API models while maintaining
    clean separation between core data and backend-specific details.
    """
    # Core Issue Data
    id: str  # Universal ID (UUID for local, external ID for remotes)
    number: int  # Human-readable number
    title: str
    description: str
    state: IssueState

    # Metadata
    created_at: datetime
    updated_at: datetime
    closed_at: Optional[datetime] = None

    # Relationships
    labels: List[Label] = field(default_factory=list)
    assignees: List[User] = field(default_factory=list)
    milestone: Optional[Milestone] = None
    comments: List[Comment] = field(default_factory=list)

    # Backend Integration
    backend_id: Optional[str] = None  # Backend-specific ID
    backend_type: Optional[str] = None  # e.g., 'local', 'gitea', 'github'
    sync_metadata: Dict[str, Any] = field(default_factory=dict)

    # Performance Optimization
    _label_categories: Optional[LabelCategories] = field(default=None, init=False)

    @cached_property
    def label_categories(self) -> LabelCategories:
        """Efficiently categorize labels with caching."""
        if self._label_categories is None:
            # Single-pass categorization for performance
            priority_labels = []
            type_labels = []
            status_labels = []
            other_labels = []

            for label in self.labels:
                if label.category == 'priority':
                    priority_labels.append(label)
                elif label.category == 'type':
                    type_labels.append(label)
                elif label.category == 'status':
                    status_labels.append(label)
                else:
                    other_labels.append(label)

            self._label_categories = LabelCategories(
                priority_labels=priority_labels,
                type_labels=type_labels,
                status_labels=status_labels,
                other_labels=other_labels
            )
        return self._label_categories

    @property
    def priority(self) -> Optional[Priority]:
        """Get issue priority from labels."""
        return self.label_categories.priority

    @property
    def issue_type(self) -> Optional[IssueType]:
        """Get issue type from labels."""
        return self.label_categories.issue_type

    @property
    def primary_assignee(self) -> Optional[User]:
        """Get primary assignee (first one)."""
        return self.assignees[0] if self.assignees else None

    def invalidate_cache(self) -> None:
        """Invalidate cached properties when labels change."""
        if hasattr(self, '_label_categories'):
            object.__setattr__(self, '_label_categories', None)

    # Domain Logic Methods
    def close(self, closed_at: Optional[datetime] = None) -> None:
        """Close the issue with business rule validation."""
        if self.state == IssueState.CLOSED:
            raise ValueError(f"Issue #{self.number} is already closed")

        self.state = IssueState.CLOSED
        self.closed_at = closed_at or datetime.now(timezone.utc)
        self.updated_at = datetime.now(timezone.utc)

    def reopen(self) -> None:
        """Reopen the issue with business rule validation."""
        if self.state != IssueState.CLOSED:
            raise ValueError(f"Issue #{self.number} is not closed (current state: {self.state.value})")

        self.state = IssueState.OPEN
        self.closed_at = None
        self.updated_at = datetime.now(timezone.utc)

    def add_label(self, label: Label) -> None:
        """Add a label to the issue."""
        if label not in self.labels:
            self.labels.append(label)
            self.invalidate_cache()
            self.updated_at = datetime.now(timezone.utc)

    def remove_label(self, label_name: str) -> bool:
        """Remove a label by name. Returns True if removed."""
        original_count = len(self.labels)
        self.labels = [label for label in self.labels if label.name != label_name]
        if len(self.labels) < original_count:
            self.invalidate_cache()
            self.updated_at = datetime.now(timezone.utc)
            return True
        return False

    def has_label(self, label_name: str) -> bool:
        """Check if issue has a specific label."""
        return any(label.name == label_name for label in self.labels)

    def add_assignee(self, user: User) -> None:
        """Add an assignee to the issue."""
        if user not in self.assignees:
            self.assignees.append(user)
            self.updated_at = datetime.now(timezone.utc)

    def remove_assignee(self, user_id: str) -> bool:
        """Remove an assignee by ID. Returns True if removed."""
        original_count = len(self.assignees)
        self.assignees = [user for user in self.assignees if user.id != user_id]
        if len(self.assignees) < original_count:
            self.updated_at = datetime.now(timezone.utc)
            return True
        return False

    def add_comment(self, comment: Comment) -> None:
        """Add a comment to the issue."""
        self.comments.append(comment)
        self.updated_at = datetime.now(timezone.utc)

    def to_dict(self) -> Dict[str, Any]:
        """Convert to dictionary for serialization."""
        return {
            'id': self.id,
            'number': self.number,
            'title': self.title,
            'description': self.description,
            'state': self.state.value,
            'created_at': self.created_at.isoformat(),
            'updated_at': self.updated_at.isoformat(),
            'closed_at': self.closed_at.isoformat() if self.closed_at else None,
            'labels': [{'name': l.name, 'color': l.color, 'description': l.description} for l in self.labels],
            'assignees': [{'id': u.id, 'username': u.username, 'display_name': u.display_name} for u in self.assignees],
            'milestone': {'id': self.milestone.id, 'title': self.milestone.title} if self.milestone else None,
            'backend_id': self.backend_id,
            'backend_type': self.backend_type,
        }

    @classmethod
    def from_dict(cls, data: Dict[str, Any]) -> 'Issue':
        """Create Issue from dictionary."""
        # This would be implemented with proper parsing
        # Simplified version for now
        raise NotImplementedError("from_dict implementation needed")