from __future__ import annotations

from datetime import date, datetime
from decimal import Decimal
from typing import Literal
from uuid import UUID

from pydantic import BaseModel, Field, field_validator

# Schema-layer bounds. The calculator + DB don't crash with these
# guard-rails — without them, year > 9999 trips ``fiscal_year_window``
# (Python date max is 9999 → ValueError), and Decimals > Numeric(4,1)
# overflow at INSERT time; both surface as 500s instead of the clean
# 422 the caller deserves. 2200 covers ~175 years of forward-dated
# projection, more than any realistic HR-tools input. _MAX_LEAVE_DAYS
# is 99.9 (matching the Numeric(4,1) column ceiling: ±999.9) — any
# single-year carry / used larger than that is a typo, and capping at
# 99.9 means the BALANCE math (settlement + carry - used, stored in
# the same Numeric(4,1) shape) can't overflow at INSERT.
_MAX_DATE = date(2200, 12, 31)
_MIN_DATE = date(1900, 1, 1)
_MAX_LEAVE_DAYS = Decimal("99.9")


# ── Calculator request / response ──────────────────────────────────


class AnnualLeaveCalculateRequest(BaseModel):
    person_id: UUID | None = Field(
        None,
        description="Selected person; lets the calculator default the employee_name "
        "/ employee_no in the persisted history row. When None the call is a free-form "
        "sandbox calculation and is still persisted but unlinked to identity_persons.",
    )
    employee_no: str | None = Field(None, max_length=64)
    employee_name: str | None = Field(None, max_length=128)
    work_start_date: date
    hire_date: date
    termination_date: date
    carry_legal_days: Decimal = Field(ge=0, le=_MAX_LEAVE_DAYS)
    carry_welfare_days: Decimal = Field(ge=0, le=_MAX_LEAVE_DAYS)
    used_legal_days: Decimal = Field(ge=0, le=_MAX_LEAVE_DAYS)
    used_welfare_days: Decimal = Field(ge=0, le=_MAX_LEAVE_DAYS)
    notes: str | None = Field(None, max_length=2000)

    @field_validator("work_start_date", "hire_date", "termination_date")
    @classmethod
    def _bound_date(cls, v: date) -> date:
        if v < _MIN_DATE or v > _MAX_DATE:
            raise ValueError(
                f"date must fall within [{_MIN_DATE}, {_MAX_DATE}]"
            )
        return v


class SegmentResponse(BaseModel):
    index: int
    start_date: date
    end_date: date
    days: int
    legal_basis: int
    welfare_basis: int
    legal_formula: str
    welfare_formula: str
    legal_raw_value: Decimal
    welfare_raw_value: Decimal


class BlockResponse(BaseModel):
    label: Literal["entitlement", "settlement"]
    range_start: date
    range_end: date
    segments: list[SegmentResponse]
    legal_raw: Decimal
    welfare_raw: Decimal
    legal_rounded: Decimal
    welfare_rounded: Decimal
    legal_capped: Decimal
    welfare_capped: Decimal
    #: 15-day combined cap (statutory kept, welfare reduced).
    cap_applied: bool
    #: 年假基数 cap — the prorated result was pulled back to the
    #: employee's own basis. Distinct rule, distinct explanation.
    basis_cap_applied: bool = False


class AnnualLeaveCalculateResponse(BaseModel):
    id: UUID  # history record id
    person_id: UUID | None
    employee_no: str | None
    employee_name: str | None
    work_start_date: date
    hire_date: date
    termination_date: date
    fiscal_year_start: date
    fiscal_year_end: date

    entitlement: BlockResponse
    settlement: BlockResponse

    carry_legal_days: Decimal
    carry_welfare_days: Decimal
    used_legal_days: Decimal
    used_welfare_days: Decimal

    # 本期余额 = 本期(结算)额度 − 当年已休; excludes carryover so that
    # period_balance + carry == balance (总余额).
    period_balance_legal_days: Decimal
    period_balance_welfare_days: Decimal

    balance_legal_days: Decimal
    balance_welfare_days: Decimal

    calculated_by_user_id: UUID
    calculated_by_name: str
    notes: str | None
    created_at: datetime


# ── History list response ──────────────────────────────────────────


class AnnualLeaveHistoryItem(BaseModel):
    id: UUID
    person_id: UUID | None
    employee_no: str | None
    employee_name: str | None
    work_start_date: date
    hire_date: date
    termination_date: date
    balance_legal_days: Decimal
    balance_welfare_days: Decimal
    calculated_by_name: str
    created_at: datetime