/** Easing and timing helpers shared by every motion template. All pure. */

export function clamp(value: number, min = 0, max = 1): number {
  return Math.min(max, Math.max(min, value));
}

export function lerp(from: number, to: number, amount: number): number {
  return from + (to - from) * amount;
}

/** Linear progress 0..1 of `t` through the window [start, end]. */
export function progress(t: number, start: number, end: number): number {
  if (end <= start) return t >= end ? 1 : 0;
  return clamp((t - start) / (end - start));
}

export function easeInCubic(x: number): number {
  return x * x * x;
}

export function easeOutCubic(x: number): number {
  return 1 - (1 - x) ** 3;
}

export function easeInOutCubic(x: number): number {
  return x < 0.5 ? 4 * x * x * x : 1 - (-2 * x + 2) ** 3 / 2;
}

export function easeOutExpo(x: number): number {
  return x >= 1 ? 1 : 1 - 2 ** (-10 * x);
}

/** Overshoots slightly before settling; for pop-in reveals. */
export function easeOutBack(x: number): number {
  const c1 = 1.70158;
  const c3 = c1 + 1;
  return 1 + c3 * (x - 1) ** 3 + c1 * (x - 1) ** 2;
}

/**
 * Opacity envelope for a clip of `durationMs`: fades in over `inMs` and out
 * over the last `outMs`.
 */
export function fadeEnvelope(t: number, durationMs: number, inMs: number, outMs: number): number {
  const fadeIn = inMs > 0 ? easeOutCubic(progress(t, 0, inMs)) : 1;
  const fadeOut = outMs > 0 ? 1 - easeInCubic(progress(t, durationMs - outMs, durationMs)) : 1;
  return clamp(Math.min(fadeIn, fadeOut));
}

/** Deterministic pseudo-random value in [0, 1) for integer seeds. */
export function hash01(a: number, b = 0): number {
  let h = Math.imul(a ^ 0x9e3779b9, 0x85ebca6b) ^ Math.imul(b + 0x632be5ab, 0xc2b2ae35);
  h = Math.imul(h ^ (h >>> 15), 0x2c1b3c6d);
  h = Math.imul(h ^ (h >>> 12), 0x297a2d39);
  return ((h ^ (h >>> 15)) >>> 0) / 4294967296;
}