// @ts-check
/**
 * A notebook picker: a list of the notebooks with "New notebook…" as its
 * last entry, which asks for the name in a field shown in the list's
 * place (not in a browser dialog).  Used on the start screen and in the
 * session's panel.  A notebook exists once a page is written into it,
 * so making one is naming it.
 */

import { listNotebooks } from './notebook.js';

/** The notebook used when none is chosen: the one for whatever has no notebook of its own. */
export const DEFAULT_NOTEBOOK = 'General';

/** The value of the "New notebook…" entry; no notebook can be named so. */
const NEW = '/new';

/** What the local program accepts as a notebook name (NAME in kokkoja.py). */
const NAME_ALLOWED = /^[^\x00-\x1f/\\:*?"<>|.][^\x00-\x1f/\\:*?"<>|]{0,119}$/;
const NAME_REFUSED = 'A notebook name cannot contain / \\ : * ? " < > | and cannot begin with a dot.';

export class NotebookPicker {
  /**
   * @param {HTMLSelectElement} select
   * @param {HTMLInputElement} entry  The field for a new name.
   * @param {(message: string) => void} say  Explains a refused name; '' clears.
   * @param {(notebook: string) => void} onChosen  The choice changed.
   */
  constructor(select, entry, say, onChosen) {
    this.select = select;
    this.entry = entry;
    this.say = say;
    this.onChosen = onChosen;
    /** The choice before "New notebook…" was picked, to return to. */
    this.previous = '';

    select.addEventListener('change', () => {
      if (select.value === NEW) this.beginNew();
      else onChosen(select.value);
    });
    entry.addEventListener('keydown', (event) => {
      if (event.key === 'Enter') {
        event.preventDefault();
        this.confirm();
      } else if (event.key === 'Escape') {
        event.preventDefault();
        this.cancel();
      }
    });
    // Leaving the field with a usable name confirms it; with none, gives up.
    entry.addEventListener('blur', () => {
      if (entry.hidden) return;
      if (NAME_ALLOWED.test(entry.value.trim())) this.confirm();
      else this.cancel();
    });
  }

  /** @returns {string}  The chosen notebook. */
  get value() {
    return this.select.value === NEW ? this.previous : this.select.value;
  }

  /**
   * List the notebooks, with the given one chosen (added to the list if
   * it is not there yet, since a notebook exists once a page is written).
   * @param {string} current
   */
  async show(current) {
    let names = /** @type {string[]} */ ([]);
    try {
      names = (await listNotebooks()).notebooks;
    } catch {
      // Without the list, the current notebook alone is offered.
    }
    this.fill(names, current);
  }

  /**
   * @param {string[]} names
   * @param {string} current
   */
  fill(names, current) {
    const all = [...new Set([...names, current])].filter(Boolean).sort((a, b) => a.localeCompare(b));
    this.select.replaceChildren();
    for (const name of all) {
      const option = document.createElement('option');
      option.value = name;
      option.textContent = name;
      this.select.append(option);
    }
    const make = document.createElement('option');
    make.value = NEW;
    make.textContent = 'New notebook…';
    this.select.append(make);
    this.select.value = current;
  }

  beginNew() {
    this.previous = this.previous || this.select.options[0]?.value || '';
    this.say('');
    this.select.hidden = true;
    this.entry.value = '';
    this.entry.hidden = false;
    this.entry.focus();
  }

  confirm() {
    const name = this.entry.value.trim();
    if (!NAME_ALLOWED.test(name)) {
      this.say(name ? NAME_REFUSED : '');
      if (!name) this.cancel();
      return;
    }
    this.say('');
    if (![...this.select.options].some((option) => option.value === name)) {
      const option = document.createElement('option');
      option.value = name;
      option.textContent = name;
      this.select.insertBefore(option, this.select.options[this.select.options.length - 1]);
    }
    this.select.value = name;
    this.previous = name;
    this.endEntry();
    this.onChosen(name);
  }

  cancel() {
    this.select.value = this.previous;
    this.endEntry();
  }

  endEntry() {
    this.entry.hidden = true;
    this.select.hidden = false;
  }

  /**
   * The choice, made from outside; it is also the one to return to if
   * "New notebook…" is given up.
   * @param {string} name
   */
  set current(name) {
    this.previous = name;
    this.select.value = name;
  }

  /** @returns {string} */
  get current() {
    return this.value;
  }
}