from pydantic import BaseModel, field_validator
from typing import Optional, List
from datetime import datetime
from enum import Enum


class DependencyType(str, Enum):
    """Task dependency types for Gantt chart."""
    FS = "FS"  # Finish-to-Start (most common)
    SS = "SS"  # Start-to-Start
    FF = "FF"  # Finish-to-Finish
    SF = "SF"  # Start-to-Finish (rare)


class TaskDependencyCreate(BaseModel):
    """Schema for creating a task dependency."""
    predecessor_id: str
    dependency_type: DependencyType = DependencyType.FS
    lag_days: int = 0

    @field_validator('lag_days')
    @classmethod
    def validate_lag_days(cls, v):
        if v < -365 or v > 365:
            raise ValueError('lag_days must be between -365 and 365')
        return v


class TaskDependencyUpdate(BaseModel):
    """Schema for updating a task dependency."""
    dependency_type: Optional[DependencyType] = None
    lag_days: Optional[int] = None

    @field_validator('lag_days')
    @classmethod
    def validate_lag_days(cls, v):
        if v is not None and (v < -365 or v > 365):
            raise ValueError('lag_days must be between -365 and 365')
        return v


class TaskInfo(BaseModel):
    """Brief task information for dependency response."""
    id: str
    title: str
    start_date: Optional[datetime] = None
    due_date: Optional[datetime] = None

    class Config:
        from_attributes = True


class TaskDependencyResponse(BaseModel):
    """Schema for task dependency response."""
    id: str
    predecessor_id: str
    successor_id: str
    dependency_type: DependencyType
    lag_days: int
    created_at: datetime
    predecessor: Optional[TaskInfo] = None
    successor: Optional[TaskInfo] = None

    class Config:
        from_attributes = True


class TaskDependencyListResponse(BaseModel):
    """Schema for list of task dependencies."""
    dependencies: List[TaskDependencyResponse]
    total: int


class DependencyValidationError(BaseModel):
    """Schema for dependency validation error details."""
    error_type: str  # 'circular', 'self_reference', 'duplicate', 'cross_project'
    message: str
    details: Optional[dict] = None