/*
 * ShrinkVertically -- optional click-and-drag horizontal scrolling of the board.
 *
 * Like the Trello board canvas: press the empty board background and drag left/right
 * to scroll #board-container horizontally. The pan only starts on empty background --
 * pressing a task card, a drag handle, or any interactive control is ignored, so this
 * never interferes with Kanboard's own card and column drag-and-drop.
 *
 * Loaded only when the "Drag the board background to scroll" setting is enabled.
 */
(function () {
    "use strict";

    // Pressing any of these (or their descendants) must NOT start a background pan.
    var IGNORE = "a, button, input, textarea, select, label, " +
        ".task-board, [data-task-id], .task-board-sort-handle, " +
        ".draggable-row-handle, .dropdown, .ui-sortable-handle";

    function isIgnored(el) {
        return !!(el && el.closest && el.closest(IGNORE));
    }

    function init() {
        var container = document.getElementById("board-container");

        if (!container || container.getAttribute("data-sv-drag") === "1") {
            return;
        }

        container.setAttribute("data-sv-drag", "1");
        container.classList.add("sv-drag-scroll");

        var dragging = false;
        var startX = 0;
        var startScrollLeft = 0;

        container.addEventListener("mousedown", function (e) {
            // Left button only, and only on empty board background.
            if (e.button !== 0 || isIgnored(e.target)) {
                return;
            }

            dragging = true;
            startX = e.clientX;
            startScrollLeft = container.scrollLeft;
            container.classList.add("sv-grabbing");
            e.preventDefault();
        });

        document.addEventListener("mousemove", function (e) {
            if (!dragging) {
                return;
            }
            container.scrollLeft = startScrollLeft - (e.clientX - startX);
            e.preventDefault();
        });

        function stop() {
            if (!dragging) {
                return;
            }
            dragging = false;
            container.classList.remove("sv-grabbing");
        }

        document.addEventListener("mouseup", stop);
        document.addEventListener("mouseleave", stop);
    }

    if (document.readyState === "loading") {
        document.addEventListener("DOMContentLoaded", init);
    } else {
        init();
    }
})();