from pydantic import BaseModel, Field, field_validator
from datetime import datetime
from typing import Optional, List

from app.schemas.category import CategoryResponse
from app.schemas.tag import TagResponse


def parse_datetime(value):
    """解析日期时间字符串"""
    if value is None or value == '':
        return None
    if isinstance(value, datetime):
        return value
    # 尝试多种格式
    formats = [
        '%Y-%m-%dT%H:%M:%S',
        '%Y-%m-%d %H:%M:%S',
        '%Y-%m-%dT%H:%M:%S.%f',
    ]
    for fmt in formats:
        try:
            return datetime.strptime(value, fmt)
        except ValueError:
            continue
    # 最后尝试 ISO 格式
    return datetime.fromisoformat(value.replace('Z', '+00:00'))


class TaskBase(BaseModel):
    """任务基础模型"""
    title: str = Field(..., max_length=200)
    description: Optional[str] = None
    priority: str = Field(default="q4", pattern="^(q1|q2|q3|q4)$")
    due_date: Optional[datetime] = None
    category_id: Optional[int] = None

    @field_validator('due_date', mode='before')
    @classmethod
    def parse_due_date(cls, v):
        return parse_datetime(v)


class TaskCreate(TaskBase):
    """创建任务请求模型"""
    tag_ids: Optional[List[int]] = []


class TaskUpdate(BaseModel):
    """更新任务请求模型

    通过 exclude_unset=True 区分"前端没传"和"前端传了 null"：
    - 前端没传某个字段 -> model_dump 结果中不包含该 key -> 不修改
    - 前端传了 null -> model_dump 结果中包含 key: None -> 视为"清空"
    """
    title: Optional[str] = Field(None, max_length=200)
    description: Optional[str] = None
    priority: Optional[str] = Field(None, pattern="^(q1|q2|q3|q4)$")
    due_date: Optional[datetime] = None
    is_completed: Optional[bool] = None
    category_id: Optional[int] = None
    tag_ids: Optional[List[int]] = None

    @field_validator('due_date', mode='before')
    @classmethod
    def parse_due_date(cls, v):
        return parse_datetime(v)

    @property
    def clearable_fields(self) -> set:
        """允许被显式清空（设为 None）的字段集合"""
        return {'description', 'due_date', 'category_id'}


class TaskResponse(TaskBase):
    """任务响应模型"""
    id: int
    is_completed: bool
    created_at: datetime
    updated_at: datetime
    category: Optional[CategoryResponse] = None
    tags: List[TagResponse] = []

    class Config:
        from_attributes = True