cmu-meal-estimator/src/engine.test.ts

import { describe, it, expect } from "vitest";
import { estimate, totalActiveDays, activeDaysConsumed } from "./engine";
import type { Config, Selections } from "./types";
import { parseISODate } from "./dates";

function d(iso: string): Date {
  const parsed = parseISODate(iso);
  if (!parsed) throw new Error(`bad test date ${iso}`);
  return parsed;
}

// A simple 100-day window (Jan 1 .. Apr 10, 2026 is 100 inclusive days).
const config: Config = {
  mealStartDate: d("2026-01-01"),
  mealEndDate: d("2026-04-10"),
  plans: [
    { id: "green", displayName: "Green", totalMealBlocks: 200, totalFlexDollars: 500 },
  ],
  missingPeriods: [
    { id: "break", displayName: "Break", startDate: d("2026-02-01"), endDate: d("2026-02-10") }, // 10 days
  ],
};

function sel(overrides: Partial<Selections> = {}): Selections {
  return {
    selectedPlanId: "green",
    targetDate: d("2026-04-10"),
    activeMissingPeriodIds: new Set(),
    extraExcludedDays: 0,
    actualMealBlocks: null,
    actualFlexDollars: null,
    ...overrides,
  };
}

describe("totalActiveDays", () => {
  it("counts the full inclusive window with no missing periods", () => {
    expect(totalActiveDays(config, new Set())).toBe(100);
  });

  it("subtracts an active missing period", () => {
    expect(totalActiveDays(config, new Set(["break"]))).toBe(90);
  });
});

describe("activeDaysConsumed", () => {
  it("is the full window at the end date", () => {
    expect(activeDaysConsumed(config, sel())).toBe(100);
  });

  it("clamps a target date before the start to zero", () => {
    expect(activeDaysConsumed(config, sel({ targetDate: d("2025-12-01") }))).toBe(0);
  });

  it("subtracts extra excluded days", () => {
    expect(activeDaysConsumed(config, sel({ extraExcludedDays: 5 }))).toBe(95);
  });
});

describe("estimate", () => {
  it("conserves the budget at the end date with no exclusions", () => {
    const r = estimate(config, sel());
    expect(r.consumedMealBlocks).toBeCloseTo(200);
    expect(r.remainingMealBlocks).toBeCloseTo(0);
    expect(r.consumedFlexDollars).toBeCloseTo(500);
    expect(r.remainingFlexDollars).toBeCloseTo(0);
  });

  it("consumed + remaining always equals the plan total", () => {
    const r = estimate(config, sel({ targetDate: d("2026-02-15"), activeMissingPeriodIds: new Set(["break"]) }));
    expect(r.consumedMealBlocks + r.remainingMealBlocks).toBeCloseTo(200);
    expect(r.consumedFlexDollars + r.remainingFlexDollars).toBeCloseTo(500);
  });

  it("computes a per-week rate of dailyRate * 7", () => {
    const r = estimate(config, sel());
    // 200 blocks / 100 days = 2/day => 14/week
    expect(r.perWeekMealBlocks).toBeCloseTo(14);
    expect(r.perWeekFlexDollars).toBeCloseTo(35); // 500/100*7
  });

  it("never lets excluding days increase consumption (monotonicity)", () => {
    const base = estimate(config, sel({ targetDate: d("2026-03-01") }));
    const more = estimate(config, sel({ targetDate: d("2026-03-01"), extraExcludedDays: 10 }));
    expect(more.consumedMealBlocks).toBeLessThanOrEqual(base.consumedMealBlocks);
  });

  it("handles zero active days without dividing by zero", () => {
    const allExcluded: Config = {
      ...config,
      missingPeriods: [
        { id: "all", displayName: "All", startDate: d("2026-01-01"), endDate: d("2026-04-10") },
      ],
    };
    const r = estimate(allExcluded, sel({ activeMissingPeriodIds: new Set(["all"]) }));
    expect(r.perWeekMealBlocks).toBe(0);
    expect(r.consumedMealBlocks).toBe(0);
    expect(Number.isFinite(r.remainingMealBlocks)).toBe(true);
  });

  it("reports activeDaysRemaining as total minus consumed", () => {
    // Halfway: Jan 1 .. Feb 19 is 50 inclusive days of a 100-day window.
    const r = estimate(config, sel({ targetDate: d("2026-02-19") }));
    expect(r.activeDaysConsumed).toBe(50);
    expect(r.activeDaysRemaining).toBe(50);
  });

  it("returns null comparisons when no actual balance is entered", () => {
    const r = estimate(config, sel());
    expect(r.blockComparison).toBeNull();
    expect(r.flexComparison).toBeNull();
  });
});

describe("balance comparison", () => {
  // Halfway through the 100-day window: expected remaining = 100 blocks / 250 flex.
  const halfway = () => sel({ targetDate: d("2026-02-19") });

  it("flags a higher-than-expected balance as ahead", () => {
    const r = estimate(config, { ...halfway(), actualMealBlocks: 130 });
    expect(r.blockComparison?.status).toBe("ahead");
    expect(r.blockComparison?.difference).toBeCloseTo(30);
  });

  it("flags a lower-than-expected balance as behind", () => {
    const r = estimate(config, { ...halfway(), actualMealBlocks: 70 });
    expect(r.blockComparison?.status).toBe("behind");
    expect(r.blockComparison?.difference).toBeCloseTo(-30);
  });

  it("flags a matching balance as on track", () => {
    const r = estimate(config, { ...halfway(), actualMealBlocks: 100 });
    expect(r.blockComparison?.status).toBe("onTrack");
  });

  it("suggests a go-forward per-week rate from the actual balance", () => {
    // 130 blocks over 50 remaining days => 2.6/day => 18.2/week.
    const r = estimate(config, { ...halfway(), actualMealBlocks: 130 });
    expect(r.blockComparison?.suggestedPerWeek).toBeCloseTo(18.2, 1);
  });

  it("suggests null per-week when no active days remain", () => {
    const r = estimate(config, { ...sel(), actualMealBlocks: 0 });
    expect(r.activeDaysRemaining).toBe(0);
    expect(r.blockComparison?.suggestedPerWeek).toBeNull();
  });
});