import { describe, expect, it } from "vitest";
import { SPRING_DEFAULT, SPRING_MOMENTUM, isSettled, stepSpring } from "../src/lib/spring";
import type { SpringConfig } from "../src/lib/spring";

/** Runs a number of frames at 16ms per frame, returning the final state and path. */
function run(from: number, target: number, config: SpringConfig, frames = 240) {
  let x = from;
  let v = 0;
  const path: number[] = [];
  for (let i = 0; i < frames; i++) {
    [x, v] = stepSpring(x, v, target, config, 16);
    path.push(x);
  }
  return { x, v, path };
}

describe("stepSpring", () => {
  it("收敛到目标", () => {
    const { x, v } = run(600, 0, SPRING_DEFAULT);
    expect(Math.abs(x)).toBeLessThan(0.5);
    expect(Math.abs(v)).toBeLessThan(5);
  });

  it("临界阻尼（damping=1）从静止出发不过冲", () => {
    const { path } = run(600, 0, SPRING_DEFAULT);
    for (const p of path) expect(p).toBeGreaterThanOrEqual(-0.5);
  });

  it("欠阻尼（damping=0.8）会过冲后回摆", () => {
    const { path } = run(600, 0, SPRING_MOMENTUM);
    expect(Math.min(...path)).toBeLessThan(-1);
  });

  it("初速度朝反方向时先随速度走再回归（速度交接语义）", () => {
    let x = 100;
    let v = 800; // moving away from target 0
    [x, v] = stepSpring(x, v, 0, SPRING_MOMENTUM, 16);
    expect(x).toBeGreaterThan(100);
    for (let i = 0; i < 240; i++) [x, v] = stepSpring(x, v, 0, SPRING_MOMENTUM, 16);
    expect(Math.abs(x)).toBeLessThan(0.5);
  });

  it("超大帧间隔（后台标签页恢复）不数值爆炸", () => {
    let x = 600;
    let v = 0;
    for (let i = 0; i < 60; i++) [x, v] = stepSpring(x, v, 0, SPRING_MOMENTUM, 500);
    expect(Number.isFinite(x)).toBe(true);
    expect(Number.isFinite(v)).toBe(true);
    expect(Math.abs(x)).toBeLessThan(1);
  });
});

describe("isSettled", () => {
  it("位置与速度双阈值", () => {
    expect(isSettled(0.4, 4, 0)).toBe(true);
    expect(isSettled(1, 0, 0)).toBe(false);
    expect(isSettled(0, 10, 0)).toBe(false);
  });
});