combobox: use popover attachment to manage positioning

src/lib/Combobox.svelte

@@ -52,6 +52,7 @@
 	import { Tween } from 'svelte/motion';
 	import { cubicOut } from 'svelte/easing';
 	import type { Attachment } from 'svelte/attachments';
+	import { Popover } from './floating.svelte';
 
 	interface Props {
 		/**
@@ -217,6 +218,39 @@
 	const id = $derived(generateIdentifier('combobox', name));
 	const searchKeySet = $derived(new Set(searchKeys));
 	const conditionalUse = $derived(use ? use : () => {});
+	const popover = new Popover({
+		interaction: 'manual',
+		placement: 'bottom-start',
+		offset: 0,
+		ontoggle: async (isOpen) => {
+			open = isOpen;
+
+			if (isOpen) {
+				scrollToHighlighted();
+
+				// focus & select search input after 100ms
+				setTimeout(() => {
+					searchInput?.focus();
+					searchInput?.select();
+				}, 100);
+
+				// handle lazy loading behaviour
+				if (lazy === 'always' || (lazy === true && !lazyApplied)) {
+					lazyApplied = true;
+					loading = true;
+					await onlazy?.();
+					loading = false;
+				}
+			} else {
+				searchValue = ''; // clear search value for next time picker opens
+				searching = false; // reset searching state
+				highlighted = value; // reset highlighted item to current value
+			}
+
+			console.log('combobox open', isOpen);
+			onopenchange?.(isOpen);
+		}
+	});
 
 	let valid = $state(true);
 	let searchValue = $state('');
@@ -227,8 +261,6 @@
 	let searchContainer = $state<HTMLDivElement | null>(null);
 	let pickerContainer = $state<HTMLDivElement | null>(null);
 
-	// TODO: there's something weird with dropdown placement on narrow screens
-
 	/** options filtered by search value and searchKeys */
 	const filteredItems = $derived.by(() => {
 		let keys: KeyOption<ComboboxOption>[] = [];
@@ -327,35 +359,11 @@
 	};
 
 	let lazyApplied = false;
-	/** opens combobox picker and propagates any necessary events */
-	const openPicker = async () => {
-		open = true;
-
-		updatePickerRect(); // update picker position
-		scrollToHighlighted(); // scroll to highlighted item
-		onopenchange?.(true); // trigger onopenchange event if defined
-
-		// handle lazy loading behaviour
-		if (lazy === 'always' || (lazy === true && !lazyApplied)) {
-			lazyApplied = true;
-			loading = true;
-			await onlazy?.();
-			loading = false;
-		}
-	};
-	/** closes combobox picker and propagates any necessary events */
-	const closePicker = () => {
-		open = false;
-		searchValue = ''; // clear search value for next time picker opens
-		searching = false; // reset searching state
-		highlighted = value; // reset highlighted item to current value
-		onopenchange?.(false); // trigger onopenchange event if defined
-	};
 
 	/** updates the value of the combobox and triggers any callbacks, including closing the picker */
 	const updateValue = (newValue: ComboboxOption) => {
 		if (!stateless) value = newValue;
-		closePicker();
+		popover.setOpen(false);
 		onchange?.(newValue);
 	};
 
@@ -397,7 +405,6 @@
 			if ((opts.mode === 'match' || opts.options.length === 0) && opts.matchElem) {
 				// match width if explicitly enabled, or no options to average
 				elem.style.width = opts.matchElem.offsetWidth + 'px';
-				console.log('matched', elem.style.width, 'to', opts.matchElem.offsetWidth);
 			} else {
 				// otherwise, set width based on average content width
 				let val = '10ch';
@@ -410,53 +417,10 @@
 					}
 				}
 				elem.style.width = val;
-				console.log('averaged', val);
 			}
 		};
 	};
 
-	/** updates the position of the picker */
-	const updatePickerRect = async () => {
-		if (!searchContainer || !pickerContainer) {
-			await tick();
-			if (!searchContainer || !pickerContainer) {
-				return;
-			}
-		}
-
-		const overlay = pickerContainer;
-		const target = searchContainer;
-		const targetRect = target.getBoundingClientRect();
-
-		if (!open) {
-			return;
-		}
-
-		// choose whether the overlay should be above or below the target
-		const availableSpaceBelow = window.innerHeight - targetRect.bottom;
-		const availableSpaceAbove = targetRect.top;
-		const outerMargin = 24;
-
-		if (availableSpaceBelow < availableSpaceAbove) {
-			// overlay should be above the target
-			overlay.style.bottom = `${window.innerHeight - targetRect.top - window.scrollY}px`;
-			overlay.style.top = 'auto';
-			overlay.style.maxHeight = `${availableSpaceAbove - outerMargin}px`;
-			pickerPosition = 'top';
-			overlay.dataset.side = 'top';
-		} else {
-			// overlay should be below the target
-			overlay.style.top = `${targetRect.bottom + window.scrollY}px`;
-			overlay.style.bottom = 'auto';
-			overlay.style.maxHeight = `${availableSpaceBelow - outerMargin}px`;
-			pickerPosition = 'bottom';
-			overlay.dataset.side = 'bottom';
-		}
-
-		// set overlay left position
-		overlay.style.left = `${targetRect.left}px`;
-	};
-
 	/** scrolls the picker to the highlighted item */
 	const scrollToHighlighted = () => {
 		if (!pickerContainer || !highlighted) return;
@@ -524,30 +488,19 @@
 
 	// close picker if clicked outside
 	const handleWindowClick: MouseEventHandler<Window> = (e) => {
-		if (!searchContainer || !pickerContainer) {
-			return;
-		}
+		if (!open || !searchContainer || !pickerContainer) return;
 
 		if (
-			!open ||
-			searchContainer.contains(e.target as Node) ||
-			pickerContainer.contains(e.target as Node)
+			e.target instanceof Node &&
+			!searchContainer.contains(e.target) &&
+			!pickerContainer.contains(e.target)
 		) {
-			return;
+			popover.setOpen(false);
 		}
-
-		closePicker();
 	};
-
-	onMount(() => {
-		// set initial picker position after load
-		setTimeout(() => {
-			updatePickerRect();
-		}, 500);
-	});
 </script>
 
-<svelte:window onresize={updatePickerRect} onclick={handleWindowClick} />
+<svelte:window onclick={handleWindowClick} />
 
 <!-- Combobox picker -->
 <Portal target="body">
@@ -567,7 +520,7 @@
 			role="listbox"
 			onkeydown={(e) => {
 				if (e.key === 'Escape') {
-					closePicker();
+					popover.setOpen(false);
 					searchInput?.focus();
 				}
 			}}
@@ -583,6 +536,7 @@
 			}}
 			tabindex="0"
 			{@attach minWidth({ options, mode: pickerWidth, matchElem: searchInput })}
+			{...popover.floating()}
 		>
 			{#each filteredItems as opt (opt.value)}
 				{@render option(opt)}
@@ -691,7 +645,7 @@
 
 <!-- Search input box -->
 {#snippet searchInputBox(caret: boolean = true)}
-	<div class="relative">
+	<div class="relative" {...popover.reference()}>
 		<!-- Persistant OR selected option icon, if visible -->
 		{#if iconVisible}
 			<div
@@ -731,13 +685,7 @@
 			autocomplete="off"
 			bind:ref={searchInput}
 			onclick={() => {
-				if (!open) {
-					setTimeout(() => {
-						searchInput?.select();
-					}, 100);
-				}
-
-				openPicker();
+				popover.setOpen(true);
 			}}
 			onkeydown={(e) => {
 				if (!searchInput) return;
@@ -747,17 +695,17 @@
 						updateValue(highlighted);
 					}
 					if (e.key === 'Enter') {
-						closePicker();
+						popover.setOpen(false);
 						e.preventDefault();
 					}
 					return;
 				} else if (e.key === 'Escape') {
-					closePicker();
+					popover.setOpen(false);
 					return;
 				}
 
 				// open the picker
-				openPicker();
+				popover.setOpen(true);
 
 				if (e.key === 'ArrowDown' || e.key === 'ArrowUp') {
 					searching = false;
@@ -804,8 +752,7 @@
 			<CaretUpDown
 				class="absolute end-2.5 top-1/2 size-6 -translate-y-1/2"
 				onclick={() => {
-					open = !open;
-					if (open) searchInput?.focus();
+					popover.setOpen(!open);
 				}}
 			/>
 		{/if}

src/routes/+page.svelte

@@ -184,7 +184,7 @@
 			]}
 			onchange={(e) => console.log('Selected:', e.value)}
 			onvalidate={(e) => console.log('Validation:', e.detail)}
-			pickerWidth="max-match"
+			pickerWidth="longest"
 		>
 			{#snippet labelRender(opt: ComboboxOption)}
 				Processed {opt.label}