// @ts-check
/**
 * The file chooser: Kokkoja's own dialog for choosing an image file
 * ("Image") and for choosing where to export a picture of the page
 * ("Export").  The browser's file chooser cannot be told where to begin
 * and cannot choose a place to write to; this one begins where the
 * notebooks are, remembers where it was last used, and reaches the whole
 * file system through the local program.
 */

import { listFiles, readFile } from './files.js';

/** Where the chooser was last used, for each of its two purposes. */
const DIRECTORY_KEYS = { image: 'kokkoja_image_directory', export: 'kokkoja_export_directory' };

/** The longer side of the small pictures of image files, in pixels. */
const SMALL_PICTURE_SIDE = 240;
/** No small picture is made of a file larger than this. */
const SMALL_PICTURE_BYTES = 32 << 20;

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

export class FileChooser {
  constructor() {
    this.dialog = /** @type {HTMLDialogElement} */ (element('file_chooser'));
    this.directoryField = /** @type {HTMLInputElement} */ (element('files_directory'));
    this.nameField = /** @type {HTMLInputElement} */ (element('files_name'));
    /** @type {'image' | 'export'} */
    this.purpose = 'image';
    /** @type {import('./files.js').DirectoryListing | null} */
    this.listing = null;
    /** Counts listings, so that work begun for an earlier one is dropped. */
    this.showing = 0;
    /** @type {((result: any) => void) | null}  Ends the present use. */
    this.finish = null;
    /** @type {((directory: string, name: string, replace: boolean) => Promise<string | null>) | null} */
    this.save = null;
    /** The name that a second press of the button may replace. */
    this.mayReplace = '';

    element('files_close').addEventListener('click', () => this.done(null));
    // Escape closes the dialog by itself.  The browser reports a close a
    // moment after it happens; if the chooser is open again by then, the
    // report is about the earlier use and must not end this one.
    this.dialog.addEventListener('close', () => {
      if (!this.dialog.open) this.done(null);
    });
    element('files_up').addEventListener('click', () => {
      if (this.listing?.parent) this.show(this.listing.parent);
    });
    this.directoryField.addEventListener('keydown', (event) => {
      if (event.key !== 'Enter') return;
      event.preventDefault();
      this.show(this.directoryField.value.trim());
    });
    this.nameField.addEventListener('input', () => this.forgetReplacing());
    this.nameField.addEventListener('keydown', (event) => {
      if (event.key !== 'Enter') return;
      event.preventDefault();
      this.saveHere();
    });
    element('files_save_here').addEventListener('click', () => this.saveHere());
  }

  /**
   * Let the user choose an image file.
   * @returns {Promise<Blob | null>}  The file, or null if none was chosen.
   */
  chooseImage() {
    return this.open('image', 'Image');
  }

  /**
   * Let the user choose a directory and a name, and save there.
   * @param {string} title
   * @param {string} name  The name to suggest.
   * @param {(directory: string, name: string, replace: boolean) => Promise<string | null>} save
   *     Writes the file and returns its full path, or null if a file of
   *     that name exists and `replace` is false.
   * @returns {Promise<string | null>}  The full path written, or null.
   */
  chooseWhereToSave(title, name, save) {
    const result = this.open('export', title);
    this.save = save;
    this.nameField.value = name;
    return result;
  }

  /**
   * @param {'image' | 'export'} purpose
   * @param {string} title
   * @returns {Promise<any>}
   */
  open(purpose, title) {
    if (this.dialog.open) return Promise.resolve(null);
    this.finish?.(null);
    this.purpose = purpose;
    element('files_title').textContent = title;
    element('files_save').hidden = purpose !== 'export';
    element('files_directories').replaceChildren();
    element('files_entries').replaceChildren();
    this.dialog.showModal();
    const result = new Promise((resolve) => { this.finish = resolve; });
    // Where it was last used; if that is gone, where the notebooks are.
    this.show(localStorage.getItem(DIRECTORY_KEYS[purpose]) ?? '').then((shown) => {
      if (!shown && this.finish) this.show('');
    });
    return result;
  }

  /** @param {any} result */
  done(result) {
    const finish = this.finish;
    this.finish = null;
    this.save = null;
    this.showing += 1;
    if (this.dialog.open) this.dialog.close();
    finish?.(result);
  }

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

  forgetReplacing() {
    this.mayReplace = '';
    element('files_save_here').textContent = 'Export';
  }

  /**
   * Show a directory.
   * @param {string} directory  A full path, or '' for where the notebooks are.
   * @returns {Promise<boolean>}  Whether it could be shown.
   */
  async show(directory) {
    const showing = this.showing += 1;
    let listing;
    try {
      listing = await listFiles(directory);
    } catch (error) {
      if (showing === this.showing) this.say(error instanceof Error ? error.message : String(error));
      return false;
    }
    if (showing !== this.showing) return true;
    this.listing = listing;
    this.directoryField.value = listing.directory;
    /** @type {HTMLButtonElement} */ (element('files_up')).disabled = listing.parent === null;
    localStorage.setItem(DIRECTORY_KEYS[this.purpose], listing.directory);
    this.forgetReplacing();

    // The directories go down the left, one to a line, and the files
    // beside them (Andy, 2026-10-05), so that neither pushes the other out
    // of view.
    const entries = element('files_entries');
    entries.replaceChildren();
    const directories = element('files_directories');
    directories.replaceChildren();
    for (const one of listing.directories) {
      const button = document.createElement('button');
      button.type = 'button';
      button.textContent = one.name;
      button.addEventListener('click', () => this.show(one.path));
      directories.append(button);
    }

    const files = this.purpose === 'image' ? listing.files
      : listing.files.filter((file) => file.name.toLowerCase().endsWith('.png'));
    if (this.purpose === 'image') this.showImages(files, entries, showing);
    else this.showExisting(files, entries);
    this.say(this.purpose === 'image' && files.length === 0 ? 'No image files here.' : '');
    return true;
  }

  /**
   * The image files of a directory, each with a small picture, made one
   * after another as the files come into view.
   * @param {import('./files.js').DirectoryListing['files']} files
   * @param {HTMLElement} entries
   * @param {number} showing
   */
  showImages(files, entries, showing) {
    const grid = document.createElement('div');
    grid.className = 'files_images';
    /** @type {Map<Element, {path: string, picture: HTMLCanvasElement}>} */
    const waiting = new Map();
    /** @type {Element[]}  Cards in view, awaiting their pictures. */
    const queue = [];
    let drawing = false;

    const drawNext = async () => {
      if (drawing) return;
      drawing = true;
      for (let card = queue.shift(); card && showing === this.showing; card = queue.shift()) {
        const entry = waiting.get(card);
        waiting.delete(card);
        if (!entry) continue;
        try {
          const bitmap = await createImageBitmap(await readFile(entry.path));
          const scale = Math.min(1, SMALL_PICTURE_SIDE / Math.max(bitmap.width, bitmap.height));
          entry.picture.width = Math.max(1, Math.round(bitmap.width * scale));
          entry.picture.height = Math.max(1, Math.round(bitmap.height * scale));
          entry.picture.getContext('2d')?.drawImage(bitmap, 0, 0, entry.picture.width, entry.picture.height);
          bitmap.close();
        } catch {
          // Not an image the browser can read: the card keeps its name only.
        }
      }
      drawing = false;
    };
    const inView = new IntersectionObserver((changes) => {
      for (const change of changes) {
        if (!change.isIntersecting || !waiting.has(change.target)) continue;
        inView.unobserve(change.target);
        queue.push(change.target);
      }
      drawNext();
    }, { root: entries });

    for (const file of files) {
      const card = document.createElement('button');
      card.type = 'button';
      card.className = 'file_card';
      const picture = document.createElement('canvas');
      picture.width = picture.height = 1;
      const name = document.createElement('span');
      name.textContent = file.name;
      card.append(picture, name);
      card.addEventListener('click', async () => {
        try {
          this.done(await readFile(file.path));
        } catch (error) {
          this.say(error instanceof Error ? error.message : String(error));
        }
      });
      grid.append(card);
      if (file.size <= SMALL_PICTURE_BYTES) {
        waiting.set(card, { path: file.path, picture });
        inView.observe(card);
      }
    }
    if (files.length) entries.append(grid);
  }

  /**
   * The PNG files already in a directory, by name: choosing one takes its
   * name, to replace it.
   * @param {import('./files.js').DirectoryListing['files']} files
   * @param {HTMLElement} entries
   */
  showExisting(files, entries) {
    const list = document.createElement('div');
    list.className = 'files_existing';
    for (const file of files) {
      const button = document.createElement('button');
      button.type = 'button';
      button.textContent = file.name;
      button.addEventListener('click', () => {
        this.nameField.value = file.name;
        this.forgetReplacing();
      });
      list.append(button);
    }
    if (files.length) entries.append(list);
  }

  /** Save into the directory shown, under the name in the name field. */
  async saveHere() {
    const save = this.save;
    const directory = this.listing?.directory;
    let name = this.nameField.value.trim();
    if (!save || !directory || !name) return;
    if (!name.toLowerCase().endsWith('.png')) name += '.png';
    this.nameField.value = name;
    try {
      const saved = await save(directory, name, this.mayReplace === name);
      if (saved !== null) {
        this.done(saved);
        return;
      }
      // No system dialog: a second press of the button replaces the file.
      this.mayReplace = name;
      element('files_save_here').textContent = 'Replace';
      this.say(`${name} exists here.`);
    } catch (error) {
      this.say(error instanceof Error ? error.message : String(error));
    }
  }
}