import { describe, expect, it } from "bun:test";
import { StateInterpolator } from "../stateInterpolation";

type NumericState = { value: number };

const interpolateNumber = (a: NumericState, b: NumericState, t: number): NumericState => ({
  value: a.value + (b.value - a.value) * t,
});

describe("StateInterpolator", () => {
  it("interpolates between history entries", () => {
    let now = 0;
    const interpolator = new StateInterpolator<NumericState>(
      { state: { value: 0 }, timestamp: 0 },
      { interpolate: interpolateNumber, getNow: () => now, interpolationDelayMs: 50 }
    );

    interpolator.addConfirmedState({ value: 10 }, { timestamp: 50 });
    interpolator.addConfirmedState({ value: 20 }, { timestamp: 100 });

    now = 130; // targetTime=80, between timestamps 50 and 100 => 60% toward 20
    expect(interpolator.getRenderState().value).toBeCloseTo(16);
  });

  it("resets history when requested", () => {
    let now = 0;
    const interpolator = new StateInterpolator<NumericState>(
      { state: { value: 0 }, timestamp: 0 },
      { interpolate: interpolateNumber, getNow: () => now, interpolationDelayMs: 0 }
    );

    interpolator.addConfirmedState({ value: 10 }, { timestamp: 50 });
    interpolator.addConfirmedState(
      { value: 20 },
      { timestamp: 100, resetHistory: true }
    );

    now = 150; // targetTime=150, only latest history entry should remain after reset
    expect(interpolator.getHistory().length).toBe(1);
    expect(interpolator.getRenderState().value).toBe(20);
  });

  it("lightly blends toward the next predicted invocation", () => {
    let now = 0;
    const interpolator = new StateInterpolator<NumericState>(
      { state: { value: 0 }, timestamp: 0, invocation: 0 },
      {
        interpolate: interpolateNumber,
        getNow: () => now,
        interpolationDelayMs: 50,
        maxPredictionBlend: 0.35,
      }
    );

    interpolator.addConfirmedState(
      { value: 10 },
      { timestamp: 100, invocation: 1 }
    );
    interpolator.setPrediction({
      state: { value: 20 },
      invocation: 2,
      timestamp: 150,
    });

    now = 200; // targetTime=150 blends 35% toward prediction
    expect(interpolator.getRenderState().value).toBeCloseTo(13.5);
  });
});