src/programs/snap-negative/policy.ts

Linked repository file from this build.

import type { SnapReview, SuaType } from "./types";
import { RuleError } from "@/lib/errors";

/** Workbook snapshot for the synthetic sample only; not a current-policy certification. */
export const demoPolicy = {
  id: "fs-negative-workbook-ffy2026-demo-v1",
  effectiveFrom: "2025-10",
  effectiveThrough: "2026-09",
  source: "FS Negative Template Workbook.xlsm: AD65:AE72, V65:AA72, AB17:AC21, T89, W11, B55",
  verification: "Workbook values transcribed; operational policy remains unverified.",
  grossLimits: [2610, 3526, 4442, 5360, 6276, 7192, 8110, 9026],
  netLimits: [1305, 1763, 2221, 2680, 3138, 3596, 4055, 4513],
  standardDeductions: [209, 209, 209, 223, 261, 299, 299, 299],
  allotments: [298, 546, 785, 994, 1183, 1421, 1571, 1789],
  sua: { heating: 857, non_heating: 488, limited: 128, telephone: 107, none: 0 } satisfies Record<
    SuaType,
    number
  >,
  shelterCap: 744,
  minimumBenefit: 24,
  homelessDeduction: 199,
  earnedDeductionPercent: 20,
} as const;

/** Full workbook table through household size 20. Values are transcribed, not extrapolated. */
export const expandedDemoPolicy = {
  ...demoPolicy,
  id: "fs-negative-workbook-ffy2026-demo-v2",
  source: "FS Negative Template Workbook.xlsm: AD65:AE84, V65:AA84, AB17:AC21, T89, W11, B55",
  grossLimits: [
    ...demoPolicy.grossLimits,
    9944,
    10862,
    11780,
    12698,
    13616,
    14534,
    15452,
    16370,
    17288,
    18206,
    19124,
    20042,
  ],
  netLimits: [
    ...demoPolicy.netLimits,
    4972,
    5434,
    5893,
    6352,
    6811,
    7270,
    7729,
    8188,
    8647,
    9106,
    9565,
    10024,
  ],
  standardDeductions: [...demoPolicy.standardDeductions, ...Array<number>(12).fill(299)],
  allotments: [
    ...demoPolicy.allotments,
    2007,
    2225,
    2443,
    2661,
    2879,
    3097,
    3315,
    3533,
    3751,
    3969,
    4187,
    4405,
  ],
} as const;

export interface SnapPolicy {
  id: string;
  effectiveFrom: string;
  source: string;
  verification: string;
  grossLimits: readonly number[];
  netLimits: readonly number[];
  standardDeductions: readonly number[];
  allotments: readonly number[];
  sua: Record<SuaType, number>;
  shelterCap: number;
  shelterDeductionPercent: number;
  minimumBenefit: number;
  homelessDeduction: number;
  earnedDeductionPercent: number;
  farmExpenseAllowancePercent: number;
  nonFarmExpenseAllowancePercent: number;
  errorThreshold: number;
  memoResponseDays: number | null;
}

/** Published FFY 2026 numbers. No FY 2027 amounts have been supplied. */
const { effectiveThrough: _effectiveThrough, ...initialAmounts } = expandedDemoPolicy;
export const initialPolicy: SnapPolicy = {
  ...initialAmounts,
  id: "snap-negative-ffy2026-v1",
  shelterDeductionPercent: 50,
  farmExpenseAllowancePercent: 100,
  nonFarmExpenseAllowancePercent: 100,
  errorThreshold: 58,
  memoResponseDays: null,
};

export function policyForMonth(sampleMonth: string, policies: readonly SnapPolicy[]): SnapPolicy {
  if (!/^\d{4}-(0[1-9]|1[0-2])$/.test(sampleMonth))
    throw new RuleError("Enter a valid sample month.");
  const policy = policies
    .filter((row) => row.effectiveFrom <= sampleMonth)
    .reduce<SnapPolicy | undefined>(
      (latest, row) => (!latest || row.effectiveFrom > latest.effectiveFrom ? row : latest),
      undefined,
    );
  if (!policy) throw new RuleError("No published policy for this sample month.");
  return policy;
}

/** Saved policy numbers remain fixed when a later table is published. */
export function resolveReviewPolicy(review: Pick<SnapReview, "policy" | "policyId">): SnapPolicy {
  if (review.policy) {
    if (review.policyId && review.policy.id !== review.policyId)
      throw new RuleError("Review policy does not match its saved ID.");
    return review.policy;
  }
  if (review.policyId && review.policyId !== initialPolicy.id)
    throw new RuleError("The saved review policy is missing.");
  return initialPolicy;
}