HealthLog/src/lib/analytics/__tests__/trend-delta.test.ts

import { describe, it, expect } from "vitest";
import { summaryToTrend7Delta } from "../trend-delta";

const STABLE = { slope: 0, direction: "stable" as const, confidence: 0.1 };
const RISING_HALF_PER_DAY = {
  slope: 0.5,
  direction: "up" as const,
  confidence: 0.8,
};
const FALLING_TENTH_PER_DAY = {
  slope: -0.1,
  direction: "down" as const,
  confidence: 0.7,
};

describe("summaryToTrend7Delta()", () => {
  it("returns null when the summary is missing", () => {
    expect(summaryToTrend7Delta(null)).toBeNull();
    expect(summaryToTrend7Delta(undefined)).toBeNull();
  });

  it("returns null when neither slope7 nor slope30 is computable", () => {
    expect(summaryToTrend7Delta({ slope7: null })).toBeNull();
    expect(summaryToTrend7Delta({ slope7: null, slope30: null })).toBeNull();
  });

  it("projects slope (units per day) over a 7-day window", () => {
    expect(summaryToTrend7Delta({ slope7: RISING_HALF_PER_DAY })).toBe(3.5);
    // Negative slope produces a negative delta — the tile shows it
    // with the unicode minus sign in the formatter.
    expect(summaryToTrend7Delta({ slope7: FALLING_TENTH_PER_DAY })).toBeCloseTo(
      -0.7,
      3,
    );
  });

  it("returns 0 for a stable slope (the tile then paints ±0)", () => {
    expect(summaryToTrend7Delta({ slope7: STABLE })).toBe(0);
  });

  it("falls back to slope30 when slope7 is null (sparse metrics like mood)", () => {
    // v1.4.16: mood-tile showed no trend number for users who
    // log mood < daily because slope7 needs ≥2 points within the
    // trailing 7-day window. slope30 still answers "is this metric
    // drifting?" so we project that onto 7 days for label parity.
    expect(
      summaryToTrend7Delta({ slope7: null, slope30: RISING_HALF_PER_DAY }),
    ).toBe(3.5);
    expect(
      summaryToTrend7Delta({
        slope7: null,
        slope30: FALLING_TENTH_PER_DAY,
      }),
    ).toBeCloseTo(-0.7, 3);
  });

  it("prefers slope7 over slope30 when both are present", () => {
    expect(
      summaryToTrend7Delta({
        slope7: RISING_HALF_PER_DAY,
        slope30: FALLING_TENTH_PER_DAY,
      }),
    ).toBe(3.5);
  });
});