functional

src/engine.test.ts

@@ -0,0 +1,98 @@
+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,
+    ...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);
+  });
+});