decision/web/src/lib/picks.svelte.ts

// The basket of the reader: the choices not sent yet, kept for the tab (a reload
// or a look at another article does not lose them), one basket per document.

import { kept, type Picks, type Votable } from './basket';
import type { Choice } from './types';

export class BasketState {
  picks = $state<Picks>({});
  #key = '';

  /**
   * Takes back the basket of this document, keeping only the choices still open: a
   * version gone leaves it, and so does a « for » on a version an objection holds back.
   */
  load(docId: string, known: Votable) {
    const key = `ld:basket:${docId}`;
    if (key === this.#key) {
      this.#keep(known);
      return;
    }
    this.#key = key;
    let saved: Picks = {};
    try {
      saved = JSON.parse(sessionStorage.getItem(key) ?? '{}') as Picks;
    } catch {
      saved = {};
    }
    this.picks = {};
    this.set(saved);
    this.#keep(known);
  }

  #keep(known: Votable) {
    const still = kept(this.picks, known);
    if (Object.keys(still).length !== Object.keys(this.picks).length) this.set(still);
  }

  set(picks: Picks) {
    const clean: Picks = {};
    for (const [id, c] of Object.entries(picks)) if (c === 'for' || c === 'against' || c === 'none') clean[id] = c;
    this.picks = clean;
    try {
      sessionStorage.setItem(this.#key, JSON.stringify(clean));
    } catch {
      /* private mode: the basket lives as long as the page */
    }
  }

  /** Picks a choice; the same choice again takes it out of the basket. */
  pick(id: string, choice: Choice) {
    const next = { ...this.picks };
    if (next[id] === choice) delete next[id];
    else next[id] = choice;
    this.set(next);
  }

  clear() {
    this.set({});
  }

  get size(): number {
    return Object.keys(this.picks).length;
  }
}