from datetime import date
from decimal import Decimal

from pydantic import BaseModel, ConfigDict, Field

TOTALS_TOLERANCE = Decimal("0.02")


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

    pay_date: date
    pay_period_start: date | None = None
    pay_period_end: date | None = None
    employer: str | None = None
    currency: str = "GBP"
    gross_pay: Decimal
    income_tax: Decimal = Field(default=Decimal("0"))
    national_insurance: Decimal = Field(default=Decimal("0"))
    pension_employee: Decimal = Field(default=Decimal("0"))
    pension_employer: Decimal = Field(default=Decimal("0"))
    student_loan: Decimal = Field(default=Decimal("0"))
    other_deductions: dict[str, Decimal] = Field(default_factory=dict)
    net_pay: Decimal


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

    document_id: int


def validate_totals(p: ExtractedPayslip) -> bool:
    """Check that gross - deductions ≈ net within a 2p tolerance.

    Employer pension is excluded — it never leaves the employer's books and
    doesn't affect take-home pay arithmetic.
    """
    deductions = (p.income_tax + p.national_insurance + p.pension_employee + p.student_loan +
                  sum(p.other_deductions.values(), start=Decimal("0")))
    diff = abs(p.gross_pay - deductions - p.net_pay)
    return diff < TOTALS_TOLERANCE