import Sqids from "sqids";

export type Slug = string & { readonly __tag: unique symbol };

export class Slugs {
  private static instance: Slugs;
  private sqids!: Sqids;

  private constructor() {
    if (Slugs.instance) return Slugs.instance;
    Slugs.instance = this;

    this.sqids = new Sqids({
      alphabet: "dbnixSPYJNy5hvsqCWIHwEKTFutV6r4Xa32okL8RQUj7Am9DcpgfZezMBG",
    });
  }

  static encode(num: number | bigint): Slug {
    const sqids = new Slugs().sqids;
    const thirtyTwoBitMax = BigInt(0xffffffff);
    if (typeof num === "bigint" && num > thirtyTwoBitMax) {
      const arr = [];
      while (num > 0) {
        arr.push(Number(num & thirtyTwoBitMax));
        num >>= 32n;
      }
      return sqids.encode(arr) as Slug;
    } else {
      return sqids.encode([Number(num)]) as Slug;
    }
  }

  static decode(slug: Slug): number | bigint {
    const ns = new Slugs().sqids.decode(slug);
    if (ns.length === 1) return ns[0];

    return ns.reduceRight((big, each) => (big << 32n) + BigInt(each), 0n);
  }
}