// The editable state of one open document, and the undo stack over it.
//
// Two rules hold this together:
//
//   1. Every mark is stored in PDF user space — points, origin bottom-left,
//      the page's own unrotated coordinate system. Not screen pixels. That
//      is the one space shared by pdf.js (viewport.convertToPdfPoint) and
//      pdf-lib (page.drawX), so a mark survives zooming, rotating and
//      reordering without a conversion table, and save-time needs no
//      knowledge of how the page happened to be displayed.
//
//   2. Marks are keyed to a page's UID, never to its position. Reordering
//      rewrites `order`; it does not touch a single annotation. A UID also
//      stays valid while a page is deleted, so undeleting restores that
//      page's marks with it.
//
// Undo is snapshot-based, like the screenshot editor's. The alternative —
// paired do/undo commands — needs a correct inverse for each of nine mark
// types plus reorder, rotate and delete, and one wrong inverse corrupts the
// document silently. A snapshot of this state is a few KB even with long pen
// paths, so there is nothing to win by being clever.

const UNDO_MAX = 60;

let seq = 0;
export function nextId(prefix = "m") { return `${prefix}${++seq}-${Math.random().toString(36).slice(2, 7)}`; }

export class DocModel {
  constructor({ name, pageCount, pageInfo }) {
    this.name = name;
    // pageInfo[i] = { width, height, rotate } straight from pdf.js, in the
    // source document's order. Immutable — it describes the file, not our
    // edits.
    this.pageInfo = pageInfo;
    this.pages = new Map();
    this.order = [];
    for (let i = 0; i < pageCount; i++) {
      const uid = `p${i}`;
      this.pages.set(uid, { uid, src: i, rotate: 0, deleted: false });
      this.order.push(uid);
    }
    this.annots = [];
    this._undo = [];
    this._redo = [];
    this._onChange = [];
    this.savedMark = this._key();   // snapshot identity at last save, for the dirty flag
  }

  onChange(fn) { this._onChange.push(fn); }
  _emit(what) { for (const fn of this._onChange) { try { fn(what); } catch (e) { console.warn("model listener threw:", e); } } }

  // ---- derived views ------------------------------------------------
  /** UIDs in display order, deleted pages left out. */
  visible() { return this.order.filter((uid) => !this.pages.get(uid).deleted); }
  page(uid) { return this.pages.get(uid); }
  /** Total rotation to display a page at: the file's own /Rotate plus ours. */
  displayRotation(uid) {
    const p = this.pages.get(uid);
    return (((this.pageInfo[p.src].rotate + p.rotate) % 360) + 360) % 360;
  }
  /** Our added rotation only — what PDFPageView.update({rotation}) wants. */
  extraRotation(uid) { return ((this.pages.get(uid).rotate % 360) + 360) % 360; }
  size(uid) { const p = this.pages.get(uid); return this.pageInfo[p.src]; }
  annotsFor(uid) { return this.annots.filter((a) => a.page === uid); }
  annot(id) { return this.annots.find((a) => a.id === id) || null; }
  deletedCount() { return this.order.filter((uid) => this.pages.get(uid).deleted).length; }

  hasRedactions() { return this.annots.some((a) => a.kind === "redact"); }
  redactedPages() {
    return new Set(this.annots.filter((a) => a.kind === "redact").map((a) => a.page));
  }
  /** True when the page list differs from the file's, so save must rebuild it. */
  pagesChanged() {
    if (this.deletedCount() > 0) return true;
    return this.order.some((uid, i) => this.pages.get(uid).src !== i);
  }
  rotationsChanged() { return this.order.some((uid) => this.pages.get(uid).rotate % 360 !== 0); }

  // ---- history ------------------------------------------------------
  _snapshot() {
    return {
      annots: structuredClone(this.annots),
      order: this.order.slice(),
      pages: this.order.map((uid) => { const p = this.pages.get(uid); return [uid, p.rotate, p.deleted]; }),
    };
  }
  _restore(s) {
    this.annots = structuredClone(s.annots);
    this.order = s.order.slice();
    for (const [uid, rotate, deleted] of s.pages) {
      const p = this.pages.get(uid);
      if (p) { p.rotate = rotate; p.deleted = deleted; }
    }
  }
  // A cheap identity for "has anything changed since the last save".
  _key() {
    return JSON.stringify([this.order, this.order.map((u) => [this.pages.get(u).rotate, this.pages.get(u).deleted]), this.annots.length,
      this.annots.map((a) => a.id)]);
  }

  /** Wrap a mutation so it lands on the undo stack as one step. */
  edit(label, fn) {
    const before = this._snapshot();
    const r = fn();
    this._undo.push({ label, before });
    if (this._undo.length > UNDO_MAX) this._undo.shift();
    this._redo = [];
    this._emit(label);
    return r;
  }
  canUndo() { return this._undo.length > 0; }
  canRedo() { return this._redo.length > 0; }
  undo() {
    const step = this._undo.pop();
    if (!step) return null;
    this._redo.push({ label: step.label, before: this._snapshot() });
    this._restore(step.before);
    this._emit("undo:" + step.label);
    return step.label;
  }
  redo() {
    const step = this._redo.pop();
    if (!step) return null;
    this._undo.push({ label: step.label, before: this._snapshot() });
    this._restore(step.before);
    this._emit("redo:" + step.label);
    return step.label;
  }
  markSaved() { this.savedMark = this._key(); this._emit("saved"); }
  isDirty() { return this._key() !== this.savedMark; }

  // ---- mutations ----------------------------------------------------
  addAnnot(a) {
    return this.edit(a.kind, () => {
      const full = { id: nextId("a"), ...a };
      this.annots.push(full);
      return full;
    });
  }
  removeAnnot(id) {
    const a = this.annot(id);
    if (!a) return false;
    return this.edit("delete " + a.kind, () => {
      this.annots = this.annots.filter((x) => x.id !== id);
      return true;
    });
  }
  /** Shift a mark by a user-space delta. `patch` is applied to the mark. */
  moveAnnot(id, patch) {
    const a = this.annot(id);
    if (!a) return false;
    return this.edit("move " + a.kind, () => { Object.assign(a, patch); return true; });
  }

  rotatePage(uid, deltaDeg) {
    return this.edit("rotate", () => {
      const p = this.pages.get(uid);
      p.rotate = (((p.rotate + deltaDeg) % 360) + 360) % 360;
      return p.rotate;
    });
  }
  setDeleted(uid, deleted) {
    return this.edit(deleted ? "delete page" : "restore page", () => {
      this.pages.get(uid).deleted = !!deleted;
      // Never leave nothing behind — a zero-page PDF cannot be written.
      if (this.visible().length === 0) { this.pages.get(uid).deleted = false; return false; }
      return true;
    });
  }
  restoreAllPages() {
    return this.edit("restore pages", () => {
      for (const uid of this.order) this.pages.get(uid).deleted = false;
      return true;
    });
  }
  /** Move `uid` so it sits immediately before `beforeUid` (or last if null). */
  reorder(uid, beforeUid) {
    if (uid === beforeUid) return false;
    return this.edit("reorder", () => {
      const from = this.order.indexOf(uid);
      if (from < 0) return false;
      this.order.splice(from, 1);
      const at = beforeUid == null ? this.order.length : this.order.indexOf(beforeUid);
      this.order.splice(at < 0 ? this.order.length : at, 0, uid);
      return true;
    });
  }
}