import json as _json

from pydantic import BaseModel, ConfigDict, Field, field_validator, model_validator
from datetime import datetime
from typing import Literal, Optional


class RecurrenceRule(BaseModel):
    """Structured recurrence rule — serialized to/from JSON string in the DB column."""
    type: Literal["every_n_days", "weekly", "monthly_nth_weekday", "monthly_date"]
    # every_n_days
    interval: Optional[int] = Field(None, ge=1, le=365)
    # weekly / monthly_nth_weekday
    weekday: Optional[int] = Field(None, ge=0, le=6)  # 0=Mon … 6=Sun
    # monthly_nth_weekday
    week: Optional[int] = Field(None, ge=1, le=4)
    # monthly_date
    day: Optional[int] = Field(None, ge=1, le=31)

    @model_validator(mode="after")
    def validate_required_fields(self):
        """Enforce required fields per rule type."""
        if self.type == "every_n_days" and self.interval is None:
            raise ValueError("every_n_days rule requires 'interval'")
        if self.type == "monthly_nth_weekday":
            if self.week is None or self.weekday is None:
                raise ValueError("monthly_nth_weekday rule requires both 'week' and 'weekday'")
        if self.type == "monthly_date" and self.day is None:
            raise ValueError("monthly_date rule requires 'day'")
        return self


def _coerce_recurrence_rule(v):
    """Accept None, dict, RecurrenceRule, or JSON/legacy strings gracefully."""
    if v is None or v == "" or v == "null":
        return None
    if isinstance(v, dict):
        return v
    if isinstance(v, RecurrenceRule):
        return v
    if isinstance(v, str):
        try:
            parsed = _json.loads(v)
            if isinstance(parsed, dict):
                return parsed
        except (_json.JSONDecodeError, TypeError):
            pass
        # Legacy simple strings like "daily", "weekly" — discard (not structured)
        return None
    return v


class CalendarEventCreate(BaseModel):
    model_config = ConfigDict(extra="forbid")

    title: str = Field(min_length=1, max_length=255)
    description: Optional[str] = Field(None, max_length=5000)
    start_datetime: datetime
    end_datetime: datetime
    all_day: bool = False
    color: Optional[str] = Field(None, max_length=20)
    location_id: Optional[int] = Field(None, ge=1, le=2147483647)
    recurrence_rule: Optional[RecurrenceRule] = None
    is_starred: bool = False
    calendar_id: Optional[int] = Field(None, ge=1, le=2147483647)

    @field_validator("recurrence_rule", mode="before")
    @classmethod
    def coerce_recurrence(cls, v):
        return _coerce_recurrence_rule(v)


class CalendarEventUpdate(BaseModel):
    model_config = ConfigDict(extra="forbid")

    title: Optional[str] = Field(None, min_length=1, max_length=255)
    description: Optional[str] = Field(None, max_length=5000)
    start_datetime: Optional[datetime] = None
    end_datetime: Optional[datetime] = None
    all_day: Optional[bool] = None
    color: Optional[str] = Field(None, max_length=20)
    location_id: Optional[int] = Field(None, ge=1, le=2147483647)
    recurrence_rule: Optional[RecurrenceRule] = None
    is_starred: Optional[bool] = None
    calendar_id: Optional[int] = Field(None, ge=1, le=2147483647)
    # Controls which occurrences an edit applies to; absent = non-recurring or whole-series
    edit_scope: Optional[Literal["this", "this_and_future"]] = None

    @field_validator("recurrence_rule", mode="before")
    @classmethod
    def coerce_recurrence(cls, v):
        return _coerce_recurrence_rule(v)


class CalendarEventResponse(BaseModel):
    id: int
    title: str
    description: Optional[str]
    start_datetime: datetime
    end_datetime: datetime
    all_day: bool
    color: Optional[str]
    location_id: Optional[int]
    recurrence_rule: Optional[str]  # raw JSON string from DB; frontend parses
    is_starred: bool
    calendar_id: int
    calendar_name: str
    calendar_color: str
    is_virtual: bool = False
    # Recurrence fields
    parent_event_id: Optional[int] = None
    is_recurring: bool = False
    original_start: Optional[datetime] = None
    created_at: datetime
    updated_at: datetime

    model_config = ConfigDict(from_attributes=True)