import type { ICountupFormatterOptions, TCountupFormatter, TEasing } from "./type";

export const ease = {
  linear: (t: number) => t,
  easeInQuad: (t: number) => t * t,
  easeOutQuad: (t: number) => t * (2 - t),
  easeInOutQuad: (t: number) => (t < 0.5 ? 2 * t * t : -1 + (4 - 2 * t) * t),
  easeOutCubic: (t: number) => --t * t * t + 1,
  easeInOutCubic: (t: number) => (t < 0.5 ? 4 * t * t * t : (t - 1) * (2 * t - 2) * (2 * t - 2) + 1),
  easeCountup: easeAsymmetricS(0.3),
} satisfies Record<string, TEasing>;

export function easeAsymmetricS(skew: number): TEasing {
  return (t: number) => {
    const s = t < skew ? (t / skew) * 0.5 : 0.5 + ((t - skew) / (1 - skew)) * 0.5;
    return s * s * (3 - 2 * s);
  };
}

/**
 * 用调用方传入的 Intl.NumberFormat 生成 formatter（实例应在工厂外创建并复用）。
 * Intl.NumberFormat 的 format getter 返回的就是已绑定函数，热路径上只剩
 * format(value) 与字符串拼接；无前后缀时直接复用 format 本身。
 */
export function buildCountupFormatter(formatter: Intl.NumberFormat, options: ICountupFormatterOptions = {}): TCountupFormatter {
  const { prefix = "", suffix = "" } = options;
  const format = formatter.format;
  if (!prefix && !suffix) return format;
  return (value: number) => prefix + format(value) + suffix;
}