progress.ts

const { noColor } = Deno;

const START = noColor ? "" : "\x1b[999D\x1b[K";
const END = noColor ? "\n" : "";

const encoder = new TextEncoder();

export class Progress {
  n: number;
  step = -1;
  writer: Deno.Writer;

  constructor(n: number, writer: Deno.Writer = Deno.stdout) {
    this.n = n;
    this.writer = writer;
  }
  async log(msg: string) {
    // We expect but don't enforce that msg doesn't contain \n.
    const line = `${START}[${this.step + 1}/${this.n}] ${msg}${END}`;
    const b = encoder.encode(line);
    await this.writer.write(b);
  }
}

export class SilentProgress extends Progress {
  async log(_: string) {}
}