/*
 * TweakDrag -- auto-scroll the board while dragging a card near a screen edge.
 *
 * Kanboard drags cards with jQuery UI sortable. The board does not scroll during a drag
 * (jQuery UI's autoscroll is unreliable horizontally, and on touch the bundled Touch Punch
 * shim suppresses native scrolling while a card is held), so you can only drop onto columns
 * already on screen. This scrolls #board-container while a card drag is active and the
 * pointer nears the left/right edge, with a smooth continuous speed that grows toward the
 * edge -- so you can drag a card to the edge and roll the board to a far column.
 *
 * It only acts during an active card drag near an edge, so it is harmless when idle. Works
 * on desktop (mouse) and mobile (touch, via Touch Punch). No core changes.
 */
(function () {
    "use strict";

    var EDGE_ZONE = 50; // px from the board edge where auto-scroll begins
    var MAX_SPEED = 22; // px per animation frame at the very edge
    var EASE = 1;       // 1 = linear ramp, 2 = gentle-then-fast

    var jq = window.jQuery;
    if (!jq) {
        return;
    }

    var container = null;
    var dragging = false;
    var rafId = 0;
    var lastX = 0;
    var lastY = 0;

    function onMove(e) {
        if (e.touches && e.touches.length) {
            lastX = e.touches[0].clientX;
            lastY = e.touches[0].clientY;
        } else {
            lastX = e.clientX;
            lastY = e.clientY;
        }
    }

    // Distance is px from the edge; returns 0 at the zone border up to MAX_SPEED at the edge.
    function speedFor(distance) {
        var p = (EDGE_ZONE - distance) / EDGE_ZONE;
        if (p <= 0) {
            return 0;
        }
        if (p > 1) {
            p = 1;
        }
        if (EASE !== 1) {
            p = Math.pow(p, EASE);
        }
        return MAX_SPEED * p;
    }

    function step() {
        if (!dragging || !container) {
            return;
        }

        var rect = container.getBoundingClientRect();
        var dLeft = lastX - rect.left;
        var dRight = rect.right - lastX;
        var speed = 0;

        if (dLeft < EDGE_ZONE) {
            speed = -speedFor(dLeft);
        } else if (dRight < EDGE_ZONE) {
            speed = speedFor(dRight);
        }

        if (speed !== 0) {
            var before = container.scrollLeft;
            container.scrollLeft = before + speed;

            // Only when the board actually moved: nudge jQuery UI to recompute drop
            // positions so the placeholder follows onto the newly revealed column.
            if (container.scrollLeft !== before) {
                document.dispatchEvent(new MouseEvent("mousemove", {
                    clientX: lastX,
                    clientY: lastY,
                    bubbles: true
                }));
            }
        }

        rafId = window.requestAnimationFrame(step);
    }

    function startLoop() {
        container = document.getElementById("board-container");
        if (!container) {
            return;
        }
        dragging = true;
        if (!rafId) {
            rafId = window.requestAnimationFrame(step);
        }
    }

    function stopLoop() {
        dragging = false;
        if (rafId) {
            window.cancelAnimationFrame(rafId);
            rafId = 0;
        }
    }

    // Track the pointer at all times (cheap; only used while dragging).
    document.addEventListener("mousemove", onMove, true);
    document.addEventListener("touchmove", onMove, true);
    document.addEventListener("pointermove", onMove, true);

    // A card drag started / stopped. jQuery UI sortable fires these (on touch too, via
    // Touch Punch); delegated on the document so board redraws need no rebinding.
    jq(document).on("sortstart", startLoop);
    jq(document).on("sortstop", stopLoop);
})();