// @ts-check
/**
 * The notebook chooser: the "Notebook" button's dialog, which shows the
 * notebooks and the pages kept in them, and loads the chosen page.
 *
 * It also deletes (Andy, 2026-10-11): every notebook and every page card
 * carries a mark at its left, a × that a tap turns into a tick (at the
 * left, since a × at the top right means "delete" itself in many
 * interfaces; a dot was tried and implied a generality that does not
 * exist), and one "Delete"
 * button in the header, which appears as soon as something is marked,
 * says how much is marked and asks for a second press before anything
 * goes, as the file chooser does for replacing a file; no system dialog.
 * One gesture serves one page and twenty.  Where the local program has
 * a Trash the entries are moved there, and the button says so;
 * in the browser they are gone for good, and the button says that.  The
 * notebook being written in cannot be marked: its mark explains.
 * Everyone has the chooser (Andy, 2026-10-11), so that a guest can see
 * and clear what their notebook holds, in a browser above all; loading
 * a page into the session is for the host and co-hosts, and a card says
 * so to anyone else.
 */

import { discardNotebook, discardPage, listKeptPages, listNotebooks, readPage } from './notebook.js';

/**
 * @param {string} id
 * @returns {HTMLElement}
 */
function element(id) {
  return /** @type {HTMLElement} */ (document.getElementById(id));
}

/**
 * @param {string} pageName
 * @returns {string}  "2026_10_02_01.svg" shown as "2026-10-02 (1)".
 */
function pageTitle(pageName) {
  const match = /^(\d{4})_(\d{2})_(\d{2})_(\d+)\.svg$/.exec(pageName);
  return match ? `${match[1]}-${match[2]}-${match[3]} (${Number(match[4])})` : pageName;
}

/**
 * @param {number} count
 * @param {string} noun
 * @returns {string}  "1 page", "3 pages".
 */
function counted(count, noun) {
  return `${count} ${noun}${count === 1 ? '' : 's'}`;
}

/**
 * A mark button: × until marked, then ✓.
 * @param {string} help  The tooltip.
 * @returns {HTMLButtonElement}
 */
function markButton(help) {
  const mark = document.createElement('button');
  mark.type = 'button';
  mark.className = 'mark';
  mark.textContent = '×';
  mark.setAttribute('aria-label', 'Mark for deletion');
  mark.setAttribute('aria-pressed', 'false');
  mark.dataset.help = help;
  return mark;
}

export class NotebookChooser {
  /**
   * @param {(notebook: string, pageName: string, text: string) => void} onChosen
   *     Called with the chosen page file.
   * @param {() => void} [onDeleted]  Called after notebooks or pages were
   *     deleted, for lists elsewhere that name them.
   */
  constructor(onChosen, onDeleted = () => {}) {
    this.onChosen = onChosen;
    this.onDeleted = onDeleted;
    this.dialog = /** @type {HTMLDialogElement} */ (element('notebook_chooser'));
    this.notebook = '';
    /** The notebook being written in, which cannot be deleted while it is. */
    this.writing = '';
    /** Whether this participant may load a page into the session. */
    this.mayLoad = true;
    /** Whether deletions go to a Trash (the local program's) or are for good. */
    this.trash = false;
    /** Counts openings, so that pictures fetched for an earlier one are dropped. */
    this.opening = 0;
    /** @type {string[]} */
    this.pictureAddresses = [];
    /** @type {Set<string>}  Notebooks marked for deletion. */
    this.markedNotebooks = new Set();
    /** @type {Map<string, Set<string>>}  Pages marked for deletion, by notebook. */
    this.markedPages = new Map();
    /** Whether the Delete button has been pressed once and awaits its second press. */
    this.armed = false;

    element('chooser_close').addEventListener('click', () => this.dialog.close());
    element('chooser_delete').addEventListener('click', () => { this.deleteMarked().catch(() => {}); });
    this.dialog.addEventListener('close', () => {
      this.forgetPictures();
      this.clearMarks();
    });
  }

  /**
   * Show the notebooks, or the pages of the only notebook.
   * @param {string} [notebook]  Open on this notebook: the one being written in.
   * @param {boolean} [mayLoad]  Whether a page may be loaded into the session.
   */
  async open(notebook, mayLoad = true) {
    this.opening += 1;
    this.writing = notebook ?? '';
    this.mayLoad = mayLoad;
    this.clearMarks();
    this.dialog.showModal();
    element('chooser_message').textContent = '';
    element('chooser_pages').replaceChildren();     // Nothing stale while the lists load.
    try {
      const { notebooks, trash } = await listNotebooks();
      this.trash = trash;
      this.showNotebooks(notebooks);
      // The notebook being written in is chosen already, its pages shown;
      // the list is always there to see (Andy, 2026-10-06).
      const chosen = notebook && notebooks.includes(notebook) ? notebook
        : notebooks.length === 1 ? notebooks[0] : '';
      await this.showPages(chosen);
    } catch (error) {
      this.say(error instanceof Error ? error.message : String(error));
    }
  }

  /** @param {string} text */
  say(text) {
    element('chooser_message').textContent = text;
  }

  /** @param {string[]} notebooks */
  showNotebooks(notebooks) {
    const list = element('chooser_notebooks');
    list.replaceChildren();
    for (const notebook of notebooks) {
      const row = document.createElement('div');
      row.className = 'notebook_row';
      const button = document.createElement('button');
      button.type = 'button';
      button.className = 'notebook_pick';
      button.textContent = notebook;
      button.addEventListener('click', () => { this.showPages(notebook); });
      const mark = markButton(notebook === this.writing
        ? 'This is the notebook you are writing in. To delete it, choose another notebook in the toolbar first.'
        : 'Mark this notebook, with every page in it, for deletion. The Delete button above then deletes what is marked.');
      if (notebook === this.writing) mark.classList.add('unavailable');
      mark.addEventListener('click', () => {
        if (notebook === this.writing) {
          this.say('You are writing in this notebook. To delete it, choose another notebook in the toolbar first.');
          return;
        }
        this.toggleMark(mark, this.markedNotebooks, notebook);
      });
      row.append(mark, button);
      list.append(row);
    }
    this.showMarks();
  }

  /** @param {string} notebook */
  async showPages(notebook) {
    this.notebook = notebook;
    this.disarm();
    for (const button of element('chooser_notebooks').querySelectorAll('button.notebook_pick')) {
      button.setAttribute('aria-pressed', String(button.textContent === notebook));
    }
    const grid = element('chooser_pages');
    grid.replaceChildren();
    this.forgetPictures();
    if (!notebook) {
      this.say('Choose a notebook.');
      return;
    }
    const opening = this.opening += 1;
    const pages = await listKeptPages(notebook);
    if (opening !== this.opening) return;
    this.say(pages.length ? '' : 'This notebook has no kept pages.');

    const marked = this.markedPages.get(notebook) ?? new Set();
    /** @type {Map<string, HTMLImageElement>} */
    const pictures = new Map();
    for (const pageName of pages) {
      const slot = document.createElement('div');
      slot.className = 'page_slot';
      const card = document.createElement('button');
      card.type = 'button';
      card.className = 'page_card';
      const picture = document.createElement('img');
      picture.alt = '';
      pictures.set(pageName, picture);
      const title = document.createElement('span');
      title.textContent = pageTitle(pageName);
      card.append(picture, title);
      card.addEventListener('click', async () => {
        if (!this.mayLoad) {
          this.say('Only the host and co-hosts can start a page for everyone from a kept page.');
          return;
        }
        const text = await readPage(notebook, pageName);
        if (text === null) return;
        this.dialog.close();
        this.onChosen(notebook, pageName, text);
      });
      const mark = markButton('Mark this page for deletion. The Delete button above then deletes what is marked.');
      mark.addEventListener('click', () => { this.toggleMark(mark, marked, pageName); });
      if (marked.has(pageName)) {
        mark.textContent = '✓';
        mark.setAttribute('aria-pressed', 'true');
        slot.classList.add('marked');
      }
      slot.append(mark, card);
      grid.append(slot);
    }
    this.markedPages.set(notebook, marked);

    // The pictures are the page files themselves, fetched one by one.
    for (const [pageName, picture] of pictures) {
      const text = await readPage(notebook, pageName);
      if (opening !== this.opening) return;
      if (text === null) continue;
      const address = URL.createObjectURL(new Blob([text], { type: 'image/svg+xml' }));
      this.pictureAddresses.push(address);
      picture.src = address;
    }
  }

  /**
   * Mark or unmark one entry.
   * @param {HTMLButtonElement} mark
   * @param {Set<string>} marked  The set the entry belongs in.
   * @param {string} name
   */
  toggleMark(mark, marked, name) {
    const now = !marked.has(name);
    if (now) marked.add(name); else marked.delete(name);
    mark.textContent = now ? '✓' : '×';
    mark.setAttribute('aria-pressed', String(now));
    /** @type {HTMLElement} */ (mark.parentElement).classList.toggle('marked', now);
    this.disarm();
    this.showMarks();
  }

  /** @returns {{notebooks: number, pages: number}}  What is marked, a marked notebook's pages not counted. */
  countMarks() {
    let pages = 0;
    for (const [notebook, names] of this.markedPages) {
      if (!this.markedNotebooks.has(notebook)) pages += names.size;
    }
    return { notebooks: this.markedNotebooks.size, pages };
  }

  /** @returns {string}  "1 notebook and 3 pages", or '' when nothing is marked. */
  describeMarks() {
    const { notebooks, pages } = this.countMarks();
    const parts = [];
    if (notebooks) parts.push(counted(notebooks, 'notebook'));
    if (pages) parts.push(counted(pages, 'page'));
    return parts.join(' and ');
  }

  /** The Delete button says what is marked, or is hidden when nothing is. */
  showMarks() {
    const button = element('chooser_delete');
    const what = this.describeMarks();
    button.hidden = !what;
    if (!what) return;
    button.textContent = this.armed
      ? (this.trash ? `Press again to move ${what} to the Trash`
        : `Press again to delete ${what} for good`)
      : `Delete ${what}?`;
  }

  /** The second press is no longer awaited: something else happened. */
  disarm() {
    if (!this.armed) return;
    this.armed = false;
    this.showMarks();
  }

  clearMarks() {
    this.markedNotebooks.clear();
    this.markedPages.clear();
    this.armed = false;
    element('chooser_delete').hidden = true;
  }

  /** The Delete button: arm on the first press, delete on the second. */
  async deleteMarked() {
    if (!this.armed) {
      this.armed = true;
      this.showMarks();
      return;
    }
    const what = this.describeMarks();
    const notebooks = [...this.markedNotebooks];
    const pages = [...this.markedPages].filter(([notebook]) => !this.markedNotebooks.has(notebook));
    this.clearMarks();
    let failed = '';
    try {
      for (const notebook of notebooks) await discardNotebook(notebook);
      for (const [notebook, names] of pages) {
        for (const name of names) await discardPage(notebook, name);
      }
    } catch (error) {
      failed = error instanceof Error ? error.message : String(error);
    }
    this.onDeleted();
    try {
      const listed = await listNotebooks();
      this.showNotebooks(listed.notebooks);
      await this.showPages(listed.notebooks.includes(this.notebook) ? this.notebook : '');
    } catch (error) {
      this.say(error instanceof Error ? error.message : String(error));
      return;
    }
    const sentence = what.charAt(0).toUpperCase() + what.slice(1);
    this.say(failed ? `Deleting stopped: ${failed}`
      : this.trash ? `${sentence} moved to the Trash.` : `${sentence} deleted.`);
  }

  forgetPictures() {
    for (const address of this.pictureAddresses) URL.revokeObjectURL(address);
    this.pictureAddresses = [];
  }
}