/*
 * Gallery editor: putting images into topics.
 *
 * Two ways in, one code path: the ⋯ menu on each thumbnail, and dragging a
 * thumbnail onto another section. Both call admin/topics-api.php and then move
 * the <figure> in place, because reloading the page after every one of a few
 * hundred assignments is not an editing experience.
 *
 * The move is optimistic and reverts on failure, so the page never shows an
 * arrangement the server did not accept.
 *
 * Deletion is deliberately not here: it stays a plain form post inside the menu,
 * with the same confirmation and the same server path it has always had.
 */
(function () {
    'use strict';

    var root = document.getElementById('topic-blocks');
    if (!root) return;

    var api = root.dataset.api;
    var slug = root.dataset.slug;
    var csrf = root.dataset.csrf;

    /* A private drag type. The uploader's dropzone reacts to "Files"; this makes
       the two kinds of drag tell themselves apart, so dragging a thumbnail never
       looks like dropping a photo from the desktop, or the other way round. */
    var DRAG_TYPE = 'application/x-gallery-image';

    var status = document.createElement('p');
    status.className = 'help topic-status';
    status.hidden = true;
    root.parentNode.insertBefore(status, root);

    function fail(message) {
        status.textContent = message;
        status.hidden = false;
    }

    function clearStatus() {
        status.hidden = true;
    }

    /* ---- Server call ---------------------------------------------------- */

    function assign(key, topic) {
        var body = new FormData();
        body.append('slug', slug);
        body.append('action', 'assign');
        body.append('key', key);
        body.append('topic', topic);
        return fetch(api, {
            method: 'POST',
            headers: { 'X-CSRF-Token': csrf },
            body: body
        }).then(function (response) {
            return response.json().catch(function () {
                return { error: 'Server returned a non-JSON response (HTTP ' + response.status + ')' };
            }).then(function (data) {
                if (!response.ok || !data.ok) {
                    throw new Error(data.error || ('Assign failed (HTTP ' + response.status + ')'));
                }
            });
        });
    }

    /* ---- Moving the thumbnail ------------------------------------------- */

    function blockFor(topic) {
        /* Topic ids are [A-Za-z0-9_-] only, so this cannot need escaping. */
        return root.querySelector('.topic-block[data-topic="' + topic + '"]');
    }

    function recount() {
        Array.prototype.forEach.call(root.querySelectorAll('.topic-block'), function (block) {
            var badge = block.querySelector('.topic-count');
            if (badge) badge.textContent = String(block.querySelectorAll('figure').length);
        });
    }

    /* Insert where the server will render it after the next reload: sections
       keep the images in their upload order, which is what data-order carries. */
    function insert(figure, row) {
        var order = parseInt(figure.dataset.order, 10) || 0;
        var after = Array.prototype.filter.call(row.children, function (el) {
            return el !== figure && (parseInt(el.dataset.order, 10) || 0) > order;
        })[0];
        row.insertBefore(figure, after || null);
    }

    function markCurrent(figure, topic) {
        Array.prototype.forEach.call(figure.querySelectorAll('.topic-pick'), function (pick) {
            pick.classList.toggle('is-current', pick.dataset.topic === topic);
        });
    }

    /* Move the thumbnail first, put it back if the server disagrees. */
    function move(figure, topic) {
        var block = blockFor(topic);
        if (!block) return;
        var row = block.querySelector('.thumb-row');
        var from = figure.parentNode;
        var before = figure.nextElementSibling;
        if (row === from) {
            closeMenus();
            return;
        }

        clearStatus();
        insert(figure, row);
        markCurrent(figure, topic);
        recount();

        assign(figure.dataset.key, topic).catch(function (err) {
            from.insertBefore(figure, before);
            markCurrent(figure, from.parentNode.dataset.topic);
            recount();
            fail(err.message);
        });
        closeMenus();
    }

    /* ---- The ⋯ menu ------------------------------------------------------ */

    function closeMenus(except) {
        Array.prototype.forEach.call(root.querySelectorAll('.thumb-menu'), function (menu) {
            if (menu === except) return;
            menu.hidden = true;
            menu.parentNode.querySelector('.thumb-menu-btn').setAttribute('aria-expanded', 'false');
        });
    }

    root.addEventListener('click', function (e) {
        var button = e.target.closest('.thumb-menu-btn');
        if (button) {
            var menu = button.parentNode.querySelector('.thumb-menu');
            var open = menu.hidden;
            closeMenus(menu);
            menu.hidden = !open;
            button.setAttribute('aria-expanded', open ? 'true' : 'false');
            return;
        }

        var pick = e.target.closest('.topic-pick');
        if (pick) {
            move(pick.closest('figure'), pick.dataset.topic);
            return;
        }

        /* A click anywhere else inside the editor, including on another
           thumbnail, dismisses an open menu. */
        if (!e.target.closest('.thumb-menu')) closeMenus();
    });

    document.addEventListener('click', function (e) {
        if (!e.target.closest || !e.target.closest('#topic-blocks')) closeMenus();
    });
    document.addEventListener('keydown', function (e) {
        if (e.key === 'Escape') closeMenus();
    });

    /* ---- Drag and drop --------------------------------------------------- */

    var dragged = null;

    root.addEventListener('dragstart', function (e) {
        var figure = e.target.closest('figure');
        if (!figure) return;
        dragged = figure;
        figure.classList.add('is-dragging');
        e.dataTransfer.effectAllowed = 'move';
        e.dataTransfer.setData(DRAG_TYPE, figure.dataset.key);
        /* Some browsers refuse a drag that sets no text/plain. */
        e.dataTransfer.setData('text/plain', figure.dataset.key);
        closeMenus();
    });

    root.addEventListener('dragend', function () {
        if (dragged) dragged.classList.remove('is-dragging');
        dragged = null;
        Array.prototype.forEach.call(root.querySelectorAll('.drag-over'), function (block) {
            block.classList.remove('drag-over');
        });
    });

    function ours(e) {
        var types = e.dataTransfer ? e.dataTransfer.types : null;
        return !!types && Array.prototype.indexOf.call(types, DRAG_TYPE) !== -1;
    }

    root.addEventListener('dragover', function (e) {
        if (!ours(e)) return;   // a file drag belongs to the uploader, not here
        var block = e.target.closest('.topic-block');
        if (!block) return;
        e.preventDefault();
        e.dataTransfer.dropEffect = 'move';
        block.classList.add('drag-over');
    });

    root.addEventListener('dragleave', function (e) {
        var block = e.target.closest('.topic-block');
        /* Ignore the leave events fired while crossing the section's own
           children, or the highlight would flicker across every thumbnail. */
        if (block && !block.contains(e.relatedTarget)) block.classList.remove('drag-over');
    });

    root.addEventListener('drop', function (e) {
        if (!ours(e)) return;
        var block = e.target.closest('.topic-block');
        if (!block) return;
        e.preventDefault();
        block.classList.remove('drag-over');
        if (dragged) move(dragged, block.dataset.topic);
    });
})();