// retoor <retoor@molodetz.nl>
export class ScrollMemory {
  static KEY = "molodetz-scroll";
  static MAX_ENTRIES = 50;
  static MAX_AGE_MS = 60 * 60 * 1000;

  constructor() {
    history.scrollRestoration = "manual";
    this.key = location.pathname + location.search;
    window.addEventListener("pagehide", () => this.save());
    const navigation = performance.getEntriesByType("navigation")[0];
    const type = navigation ? navigation.type : "navigate";
    if (type === "back_forward" || type === "reload" || sessionStorage.getItem("molodetz-restore") === this.key) {
      sessionStorage.removeItem("molodetz-restore");
      this.restore();
    }
    document.addEventListener("click", (event) => {
      const link = event.target.closest(".breadcrumbs a, a[data-back]");
      if (link) {
        sessionStorage.setItem("molodetz-restore", new URL(link.href).pathname);
      }
    });
  }

  read() {
    try {
      return JSON.parse(sessionStorage.getItem(ScrollMemory.KEY) || "{}");
    } catch {
      return {};
    }
  }

  save() {
    const entries = this.read();
    entries[this.key] = { y: window.scrollY, at: Date.now() };
    const now = Date.now();
    const kept = Object.entries(entries)
      .filter(([, value]) => now - value.at < ScrollMemory.MAX_AGE_MS)
      .sort((a, b) => b[1].at - a[1].at)
      .slice(0, ScrollMemory.MAX_ENTRIES);
    sessionStorage.setItem(ScrollMemory.KEY, JSON.stringify(Object.fromEntries(kept)));
  }

  restore() {
    const entry = this.read()[this.key];
    if (!entry) {
      return;
    }
    const deadline = performance.now() + 1500;
    let aborted = false;
    const abort = () => { aborted = true; };
    ["wheel", "touchstart", "keydown"].forEach((name) => window.addEventListener(name, abort, { once: true, passive: true }));
    const apply = () => {
      if (aborted) {
        return;
      }
      window.scrollTo(0, entry.y);
      if (Math.abs(window.scrollY - entry.y) > 2 && performance.now() < deadline) {
        requestAnimationFrame(apply);
      }
    };
    requestAnimationFrame(apply);
  }
}