import {
  easeToward,
  locateInReel,
  pickActiveCard,
  reelStarts,
  videoProgress,
} from "./showcase-math";

const card = (id: string, visible: boolean, distance: number) => ({
  id,
  visible,
  distance,
});

describe("pickActiveCard", () => {
  it("plays the visible card closest to the middle of the screen", () => {
    expect(
      pickActiveCard(
        [card("a", true, 300), card("b", true, 80), card("c", false, 5)],
        null,
      ),
    ).toBe("b");
  });

  it("lets the hovered card win over a closer one, but only while it is visible", () => {
    const cards = [card("a", true, 10), card("b", true, 400)];
    expect(pickActiveCard(cards, "b")).toBe("b");
    expect(
      pickActiveCard([card("a", true, 10), card("b", false, 0)], "b"),
    ).toBe("a");
  });

  it("keeps the first card on a tie, so the left one of a row wins", () => {
    expect(
      pickActiveCard(
        [card("left", true, 120), card("right", true, 120.3)],
        null,
      ),
    ).toBe("left");
  });

  it("plays nothing when no card is on screen", () => {
    expect(pickActiveCard([card("a", false, 0)], null)).toBeNull();
    expect(pickActiveCard([], null)).toBeNull();
  });
});

describe("locateInReel", () => {
  const weights = [1, 2, 1];

  it("maps overall progress to a project and a position inside it", () => {
    expect(locateInReel(weights, 0)).toEqual({ index: 0, local: 0 });
    expect(locateInReel(weights, 0.125)).toEqual({ index: 0, local: 0.5 });
    const middle = locateInReel(weights, 0.5);
    expect(middle.index).toBe(1);
    expect(middle.local).toBeCloseTo(0.5);
    expect(locateInReel(weights, 1)).toEqual({ index: 2, local: 1 });
  });

  it("clamps progress outside the pinned range", () => {
    expect(locateInReel(weights, -3)).toEqual({ index: 0, local: 0 });
    expect(locateInReel(weights, 7)).toEqual({ index: 2, local: 1 });
  });

  it("copes with an empty reel", () => {
    expect(locateInReel([], 0.4)).toEqual({ index: 0, local: 0 });
  });

  it("gives each project the share of the scroll that its weight asks for", () => {
    expect(reelStarts(weights)).toEqual([0, 0.25, 0.75]);
  });
});

describe("videoProgress", () => {
  it("holds still at the start and at the end of each project's stretch", () => {
    expect(videoProgress(0)).toBe(0);
    expect(videoProgress(0.1)).toBe(0);
    expect(videoProgress(0.5)).toBeCloseTo(0.5);
    expect(videoProgress(0.9)).toBe(1);
    expect(videoProgress(1)).toBe(1);
  });
});

describe("easeToward", () => {
  it("moves toward the target and never overshoots", () => {
    const first = easeToward(0, 1, 1 / 60);
    expect(first).toBeGreaterThan(0);
    expect(first).toBeLessThan(1);
    expect(easeToward(0.5, 0.5, 1)).toBe(0.5);
    expect(easeToward(0, 1, 10)).toBeCloseTo(1, 5);
  });

  it("does not depend on the frame rate", () => {
    let sixty = 0;
    for (let i = 0; i < 60; i += 1) sixty = easeToward(sixty, 1, 1 / 60);
    let thirty = 0;
    for (let i = 0; i < 30; i += 1) thirty = easeToward(thirty, 1, 1 / 30);
    expect(sixty).toBeCloseTo(thirty, 6);
  });

  it("stands still when no time has passed", () => {
    expect(easeToward(0.2, 1, 0)).toBe(0.2);
  });
});