feat(pat-stacks): Add configurable scroll support.

Add "scroll-selector" and "scroll-offset" arguments to pat-stacks,
likewise as in pat-collapsible. "scroll-selector" accepts a CSS selector
string or the special values "self" to scroll to the element itself and
"none" to block any scrolling behavior from parent pat-stacks configuration
options.

With these configuration options you can control the scrolling behavior
for pat-stacks on a fine-grained level.

src/pat/stacks/documentation.md

@@ -45,3 +45,5 @@ The Stacks pattern may be configured through a `data-pat-stacks` attribute. The
 | `transition`      | `none`  | Transition effect to use. Must be one of `none`, `css`, `fade` or `slide`.                                                                                 |
 | `effect-duration` | `fast`  | Duration of transition. This is ignored if the transition is `none` or `css`.                                                                              |
 | `effect-easing`   | `swing` | Easing to use for the transition. This must be a known jQuery easing method. jQuery includes `swing` and `linear`, but more can be included via jQuery UI. |
+| `scroll-selector` |         | CSS selector, `self` or `none`. Defines which element will be scrolled into view. `self` if it is the stacks content element itself. `none` to disable scrolling if a scrolling selector is inherited from a parent pat-stacks element. |
+| `scroll-offset`   |         | `offset` in pixels to stop scrolling before the target position defined by `scroll-selector`. Can also be a negative number.                               |

src/pat/stacks/stacks.js

@@ -1,7 +1,8 @@
 import $ from "jquery";
 import { BasePattern } from "../../core/basepattern";
-import Parser from "../../core/parser";
+import events from "../../core/events";
 import logging from "../../core/logging";
+import Parser from "../../core/parser";
 import registry from "../../core/registry";
 import utils from "../../core/utils";
 
@@ -12,15 +13,39 @@ parser.addArgument("selector", "> *[id]");
 parser.addArgument("transition", "none", ["none", "css", "fade", "slide"]);
 parser.addArgument("effect-duration", "fast");
 parser.addArgument("effect-easing", "swing");
+// pat-scroll support
+parser.addArgument("scroll-selector");
+parser.addArgument("scroll-offset", 0);
+
+const debounce_scroll_timer = { timer: null };
 
 class Pattern extends BasePattern {
     static name = "stacks";
     static trigger = ".pat-stacks";
     static parser = parser;
     document = document;
 
-    init() {
+    async init() {
         this.$el = $(this.el);
+
+        // pat-scroll support
+        if (this.options.scroll?.selector && this.options.scroll.selector !== "none") {
+            const Scroll = (await import("../scroll/scroll")).default;
+            this.scroll = new Scroll(this.el, {
+                trigger: "manual",
+                selector: this.options.scroll.selector,
+                offset: this.options.scroll?.offset,
+            });
+            await events.await_pattern_init(this.scroll);
+
+            // scroll debouncer for later use.
+            this.debounce_scroll = utils.debounce(
+                this.scroll.scrollTo.bind(this.scroll),
+                10,
+                debounce_scroll_timer
+            );
+        }
+
         this._setupStack();
         $(this.document).on("click", "a", this._onClick.bind(this));
     }
@@ -78,6 +103,10 @@ class Pattern extends BasePattern {
         e.preventDefault();
         this._updateAnchors(href_parts[1]);
         this._switch(href_parts[1]);
+
+        this.debounce_scroll?.(); // debounce scroll, if available.
+
+        // Notify other patterns
         $(e.target).trigger("pat-update", {
             pattern: "stacks",
             action: "attribute-changed",

src/pat/stacks/stacks.test.js

@@ -1,6 +1,7 @@
 import $ from "jquery";
 import events from "../../core/events";
 import Stacks from "./stacks";
+import utils from "../../core/utils";
 import { jest } from "@jest/globals";
 
 describe("pat-stacks", function () {
@@ -164,4 +165,65 @@ describe("pat-stacks", function () {
             expect($("#l2").hasClass("current")).toBe(true);
         });
     });
+
+    describe("5 - Scrolling support.", function () {
+        beforeEach(function () {
+            document.body.innerHTML = "";
+            this.spy_scrollTo = jest
+                .spyOn(window, "scrollTo")
+                .mockImplementation(() => null);
+        });
+
+        afterEach(function () {
+            this.spy_scrollTo.mockRestore();
+        });
+
+        it("5.1 - Scrolls to self.", async function () {
+            document.body.innerHTML = `
+                <a href='#s51'>1</a>
+                <div class="pat-stacks" data-pat-stacks="scroll-selector: self">
+                    <section id="s51">
+                    </section>
+                </div>
+            `;
+            const el = document.querySelector(".pat-stacks");
+
+            const instance = new Stacks(el);
+            await events.await_pattern_init(instance);
+
+            const s51 = document.querySelector("[href='#s51']");
+            $(s51).click();
+            await utils.timeout(10);
+
+            expect(this.spy_scrollTo).toHaveBeenCalled();
+        });
+
+        it("5.2 - Does clear scroll setting from parent config.", async function () {
+            // NOTE: We give the stack section a different id.
+            // The event handler which is registered on the document in the
+            // previous test is still attached. Two event handlers are run when
+            // clicking here and if the anchor-targets would have the same id
+            // the scrolling would happen as it was set up in the previous
+            // test.
+            document.body.innerHTML = `
+                <div data-pat-stacks="scroll-selector: self">
+                    <a href='#s52'>1</a>
+                    <div class="pat-stacks" data-pat-stacks="scroll-selector: none">
+                        <section id="s52">
+                        </section>
+                    </div>
+                </div>
+            `;
+            const el = document.querySelector(".pat-stacks");
+
+            const instance = new Stacks(el);
+            await events.await_pattern_init(instance);
+
+            const s52 = document.querySelector("[href='#s52']");
+            $(s52).click();
+            await utils.timeout(10);
+
+            expect(this.spy_scrollTo).not.toHaveBeenCalled();
+        });
+    });
 });