import { SvelteMap } from 'svelte/reactivity';
import { withoutMarkers, type Attached } from './attachments';

// What was typed in a chat's composer and not yet sent. The composer is
// destroyed with its window when another board is shown or the page goes, so
// a draft lives here, by session, and in localStorage. Only the text is kept
// there: images are too big for it, so a reload drops them and their markers.

const KEY = 'albedo.draft.v1:';
/** A draft untouched this long is not worth keeping; the session may be gone. */
const STALE_MS = 30 * 24 * 60 * 60 * 1000;
const SAVE_AFTER_MS = 300;

function read(session: string): string {
  try {
    const saved = JSON.parse(localStorage.getItem(KEY + session) ?? '');
    return typeof saved?.text === 'string' ? withoutMarkers(saved.text) : '';
  } catch {
    return '';
  }
}

/** Drops the saved drafts nobody came back to. */
function prune() {
  try {
    for (const key of Object.keys(localStorage).filter((name) => name.startsWith(KEY))) {
      const saved = JSON.parse(localStorage.getItem(key) ?? 'null');
      if (!(Date.now() - saved?.at < STALE_MS)) localStorage.removeItem(key);
    }
  } catch {}
}

const unsaved = new Set<Draft>();
let timer: ReturnType<typeof setTimeout> | undefined;

function flush() {
  clearTimeout(timer);
  timer = undefined;
  for (const draft of unsaved) draft.save();
  unsaved.clear();
}

export class Draft {
  readonly images = new SvelteMap<number, Attached>();
  /** The last image marker handed out. */
  next = 0;
  #text: string;
  #session: string;

  constructor(session: string) {
    this.#session = session;
    this.#text = read(session);
  }

  get text(): string {
    return this.#text;
  }

  /** Setting the text saves it a moment later, once typing pauses. */
  set text(value: string) {
    if (value === this.#text) return;
    this.#text = value;
    unsaved.add(this);
    timer ??= setTimeout(flush, SAVE_AFTER_MS);
  }

  save() {
    try {
      const text = withoutMarkers(this.#text);
      if (text.trim()) localStorage.setItem(KEY + this.#session, JSON.stringify({ text, at: Date.now() }));
      else localStorage.removeItem(KEY + this.#session);
    } catch {}
  }
}

const drafts = new Map<string, Draft>();

export function draftOf(session: string): Draft {
  let draft = drafts.get(session);
  if (!draft) drafts.set(session, (draft = new Draft(session)));
  return draft;
}

if (typeof window !== 'undefined') {
  prune();
  // The last words typed before a reload or a closed tab are still waiting on the timer.
  window.addEventListener('pagehide', flush);
}