.pragma library
// Copyright (C) 2026 Danilo M. <danix@danix.xyz>
//
// This program is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License version 2 as
// published by the Free Software Foundation.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.

// The wallpaper engine's order, tested by test_shuffle.js under node: a
// shuffle bag. Each round shows every path once in random order, and a new
// round never opens with the path on screen, so a reshuffle cannot show the
// same picture twice running.

// The next path and what is left of the round. `list` is what may be shown
// now, so a heart removed since the last draw drops out of the bag; `last` is
// the path on screen. pick is "" for an empty list.
function draw(list, bag, last) {
    let left = bag.filter(p => list.indexOf(p) >= 0);
    if (left.length === 0) left = shuffled(list, last);
    return { pick: left.length ? left[0] : "", bag: left.slice(1) };
}

function shuffled(list, last) {
    const a = list.slice();
    for (let i = a.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1));
        const t = a[i]; a[i] = a[j]; a[j] = t;
    }
    if (a.length > 1 && a[0] === last) { const t = a[0]; a[0] = a[1]; a[1] = t; }
    return a;
}