floating: add constraint size option

src/lib/floating.svelte.ts

@@ -4,7 +4,7 @@
  * for more details, examples, and original source.
  */
 
-import { computePosition, autoUpdate, flip, offset, type Placement } from '@floating-ui/dom';
+import { computePosition, autoUpdate, flip, offset, type Placement, size } from '@floating-ui/dom';
 import { createAttachmentKey } from 'svelte/attachments';
 
 /**
@@ -17,6 +17,13 @@ export interface PopoverOptions {
 	placement?: Placement;
 	/** Offset distance between the reference and floating elements (default: 8) */
 	offset?: number;
+	/**
+	 * Constraints the width and height of the popover to prevent it from
+	 * overflowing the viewport. If true, the popover will adjust its max-width
+	 * and max-height to fit. Scrolling is the responsibility of the parent
+	 * element. Default is true.
+	 */
+	constrainSize?: boolean;
 	/** Callback when the popover is opened or closed */
 	ontoggle?: (open: boolean) => void;
 }
@@ -29,7 +36,8 @@ export class Popover {
 	private options: PopoverOptions = {
 		interaction: 'click',
 		placement: 'bottom-start',
-		offset: 8
+		offset: 8,
+		constrainSize: true
 	};
 	private referenceElement: HTMLElement | undefined = $state();
 	private floatingElement: HTMLElement | undefined = $state();
@@ -165,7 +173,21 @@ export class Popover {
 		}
 		const position = await computePosition(this.referenceElement, this.floatingElement, {
 			placement: this.options.placement,
-			middleware: [flip(), offset(this.options.offset)]
+			middleware: [
+				flip(),
+				offset(this.options.offset),
+				size({
+					apply: ({ availableWidth, availableHeight, elements }) => {
+						if (this.options.constrainSize) {
+							elements.floating.style.maxWidth = `${availableWidth}px`;
+							elements.floating.style.maxHeight = `${availableHeight}px`;
+						} else {
+							elements.floating.style.maxWidth = '';
+							elements.floating.style.maxHeight = '';
+						}
+					}
+				})
+			]
 		});
 		const { x, y } = position;
 		Object.assign(this.floatingElement.style, {