class SimpleProgressBar {
  #container = document.createElement("div");
  #progress = document.createElement("div");
  #textDiv = document.createElement("div");
  #text = document.createElement("span");
  #visible = false;
  #hideTimeout = null;
  #interval = null;
  #max = 0;
  /** @type {Set} */
  #monitoredSet;

  constructor() {
    this.#container.style.cssText = "position:relative;width:100%;background-color:hsla(0,0%,36%,0.3);height:1.2rem;margin:0;padding:0;display:none;"
    this.#progress.style.cssText = "position:absolute;left:0;height:100%;width:0;transition:width 200ms;"
    this.#progress.style.backgroundColor = "hsla(110, 32%, 35%, 0.80)";  // alt: "#27911d"
    this.#textDiv.style.cssText = "margin:auto;width:max-content;height:100%;";
    this.#text.style.cssText = "position:relative;user-select:none;color:white;"

    this.#textDiv.append(this.#text);
    this.#container.append(this.#progress, this.#textDiv);
  }

  setMax(max) {
    this.clearProgress();
    this.#max = max;
    this.#startUpdating();
  }

  attach(element) {
    if (element.hasChildNodes) {
      element.innerHTML = '';
    }
    element.appendChild(this.#container);
  }

  monitor(hashes) {
    // This is required because incrementing a variable with a class method turned out to not be an atomic operation
    this.#monitoredSet = hashes;
  }

  clearProgress() {
    this.#stopUpdating();
    clearTimeout(this.#hideTimeout);
    this.#hideTimeout = null;
    this.#container.style.display = "none";
    this.#visible = false;
    this.#progress.style.width = "0";
    this.#text.textContent = "";
  }

  #setProgress(loaded, max) {
    if (this.#hideTimeout) {
      this.#hideTimeout = null;
    }

    this.#progress.style.width = `${Math.floor((loaded / max) * 100)}%`;
    this.#text.textContent = `${loaded}/${max}`;

    if (!this.#visible) {
      this.#container.style.display = "block";
      this.#visible = true;
    }
    if (loaded >= max) {
      this.#stopUpdating()
      this.#hideTimeout = setTimeout(() => {
        this.clearProgress();
      }, 1000);
    }
  }

  #startUpdating() {
    this.#interval = setInterval(() => {
      this.#setProgress(this.#monitoredSet.size, this.#max);
    }, 250);
  }

  #stopUpdating() {
    clearInterval(this.#interval);
    this.#interval = null;
  }
}