import { describe, expect, it } from "vitest";
import { planWheelScroll } from "../web/chat-scroll.js";

describe("planWheelScroll", () => {
  it("rolls the card first and leaves the big scroller alone", () => {
    const plan = planWheelScroll({
      cardScrollTop: 0,
      cardScrollMax: 400,
      deltaY: 100,
      streamScrollTop: 0,
      streamScrollMax: 2000,
    });
    expect(plan.cardDelta).toBe(100);
    expect(plan.streamDelta).toBe(0);
    expect(plan.rest).toBe(0);
  });

  it("hands the leftover to the big scroller once the card hits its bottom", () => {
    const plan = planWheelScroll({
      cardScrollTop: 380,
      cardScrollMax: 400,
      deltaY: 100,
      streamScrollTop: 0,
      streamScrollMax: 2000,
    });
    expect(plan.cardDelta).toBe(20);
    expect(plan.streamDelta).toBe(80);
    expect(plan.rest).toBe(0);
  });

  it("skips the card when it is already at the bottom", () => {
    const plan = planWheelScroll({
      cardScrollTop: 400,
      cardScrollMax: 400,
      deltaY: 100,
      streamScrollTop: 0,
      streamScrollMax: 2000,
    });
    expect(plan.cardDelta).toBe(0);
    expect(plan.streamDelta).toBe(100);
  });

  it("scrolls up the card first, then the big scroller", () => {
    const plan = planWheelScroll({
      cardScrollTop: 10,
      cardScrollMax: 400,
      deltaY: -100,
      streamScrollTop: 500,
      streamScrollMax: 2000,
    });
    expect(plan.cardDelta).toBe(-10);
    expect(plan.streamDelta).toBe(-90);
  });

  it("treats a card that cannot scroll as no card at all", () => {
    const plan = planWheelScroll({
      cardScrollTop: 0,
      cardScrollMax: 0,
      deltaY: 120,
      streamScrollTop: 0,
      streamScrollMax: 2000,
    });
    expect(plan.cardDelta).toBe(0);
    expect(plan.streamDelta).toBe(120);
  });

  it("stops at the ends of both scrollers", () => {
    const down = planWheelScroll({
      cardScrollTop: 400,
      cardScrollMax: 400,
      deltaY: 100,
      streamScrollTop: 2000,
      streamScrollMax: 2000,
    });
    expect(down.cardDelta).toBe(0);
    expect(down.streamDelta).toBe(0);
    expect(down.rest).toBe(100);

    const up = planWheelScroll({
      cardScrollTop: 0,
      cardScrollMax: 400,
      deltaY: -100,
      streamScrollTop: 0,
      streamScrollMax: 2000,
    });
    expect(up.rest).toBe(-100);
  });

  it("keeps fractional trackpad deltas", () => {
    const plan = planWheelScroll({
      cardScrollTop: 12.5,
      cardScrollMax: 400,
      deltaY: 7.25,
    });
    expect(plan.cardDelta).toBeCloseTo(7.25, 5);
    expect(plan.rest).toBeCloseTo(0, 5);
  });

  it("does nothing without a delta", () => {
    const plan = planWheelScroll({ cardScrollMax: 400, streamScrollMax: 800 });
    expect(plan).toEqual({ cardDelta: 0, streamDelta: 0, rest: 0 });
  });
});