combobox: improve props, fix placement with scroll

src/lib/Combobox.svelte

@@ -28,29 +28,15 @@
 	import { Portal } from '@jsrob/svelte-portal';
 	import { browser } from '$app/environment';
 	import { scale } from 'svelte/transition';
+	import { generateIdentifier } from './util.js';
 
-	let {
-		name,
-		value = $bindable<ComboboxItem | undefined>(undefined),
-		open = $bindable(false),
-		usePreview = 'auto',
-		matchWidth = false,
-		items,
-		required = false,
-		invalidMessage,
-		label,
-		placeholder,
-		notFoundMessage = 'No results found',
-		onvalidate,
-		onchange
-	}: {
-		name: string;
+	interface Props {
+		name?: string;
 		value?: ComboboxItem;
-		highlighted?: ComboboxItem;
 		open?: boolean;
 		usePreview?: boolean | 'auto';
 		matchWidth?: boolean;
-		items: ComboboxItem[];
+		options: ComboboxItem[];
 		required?: boolean;
 		invalidMessage?: string;
 		label?: string;
@@ -58,7 +44,25 @@
 		notFoundMessage?: string;
 		onvalidate?: (e: InputValidatorEvent) => void;
 		onchange?: (e: ComboboxChangeEvent) => void;
-	} = $props();
+	}
+
+	let {
+		name,
+		value = $bindable<ComboboxItem | undefined>(undefined),
+		open = $bindable(false),
+		usePreview = 'auto',
+		matchWidth = false,
+		options,
+		required = false,
+		invalidMessage,
+		label,
+		placeholder,
+		notFoundMessage = 'No results found',
+		onvalidate,
+		onchange
+	}: Props = $props();
+
+	let id = $derived(generateIdentifier('combobox', name));
 
 	let valid = $state(true);
 	let searchValue = $state('');
@@ -71,8 +75,8 @@
 
 	const filteredItems = $derived(
 		searchValue === ''
-			? items
-			: items.filter((item) => getLabel(item).toLowerCase().includes(searchValue.toLowerCase()))
+			? options
+			: options.filter((item) => getLabel(item).toLowerCase().includes(searchValue.toLowerCase()))
 	);
 
 	let highlighted = $derived.by((): ComboboxItem | undefined => {
@@ -95,15 +99,15 @@
 		return filteredItems.findIndex((item) => item.value === highlighted?.value);
 	};
 
-	const minWidth: Action<HTMLDivElement, { items: ComboboxItem[] }> = (container, buildOpts) => {
+	const minWidth: Action<HTMLDivElement, { options: ComboboxItem[] }> = (container, buildOpts) => {
 		const f = (opts: typeof buildOpts) => {
 			if (matchWidth && searchInput) {
 				container.style.width = searchInput.scrollWidth + 'px';
 				return;
 			}
 
-			const items = opts.items;
-			const avg = items.reduce((acc, item) => acc + getLabel(item).length, 0) / items.length;
+			const options = opts.options;
+			const avg = options.reduce((acc, item) => acc + getLabel(item).length, 0) / options.length;
 			container.style.width = `${avg * 2.5}ch`;
 			console.log(`minWidth: ${avg * 2.5}ch`);
 		};
@@ -139,13 +143,15 @@
 		const outerMargin = 24;
 
 		if (availableSpaceBelow < availableSpaceAbove) {
-			overlay.style.bottom = `${window.innerHeight - targetRect.top}px`;
+			// overlay should be above the target
+			overlay.style.bottom = `${window.innerHeight - targetRect.top - window.scrollY}px`;
 			overlay.style.top = 'auto';
 			overlay.style.maxHeight = `${availableSpaceAbove - outerMargin}px`;
 			pickerPosition = 'top';
 			overlay.dataset.side = 'top';
 		} else {
-			overlay.style.top = `${targetRect.bottom}px`;
+			// 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';
@@ -197,7 +203,7 @@
 	}
 
 	// when the picker is opened, update its position
-	// when the picker is closed, clear any search value (next time it opens, all items will be shown)
+	// when the picker is closed, clear any search value (next time it opens, all options will be shown)
 	// when the picker is closed, reset highlighted to the currently selected value (if any)
 	$effect(() => {
 		if (open) {
@@ -253,7 +259,7 @@
 				open && pickerPosition === 'top' && 'mb-[var(--outer-gap)]',
 				open && pickerPosition === 'bottom' && 'mt-[var(--outer-gap)]'
 			]}
-			use:minWidth={{ items: items }}
+			use:minWidth={{ options: options }}
 			bind:this={pickerContainer}
 			transition:scale={{ duration: 200 }}
 			role="listbox"
@@ -272,7 +278,7 @@
 					aria-label={getLabel(item)}
 					aria-disabled={item.disabled}
 					class={[
-						'picker-item mb-0.5 flex min-h-10 flex-wrap items-center py-2.5 pr-1.5 pl-5',
+						'picker-item options-center mb-0.5 flex min-h-10 flex-wrap py-2.5 pr-1.5 pl-5',
 						'rounded-sm text-sm capitalize outline-hidden select-none',
 						'hover:bg-accent-500/30 dark:hover:bg-accent-700/30',
 						item.value === highlighted?.value && 'bg-accent-500/80 dark:bg-accent-700/80'
@@ -321,12 +327,13 @@
 <div>
 	<!-- Combobox Label -->
 	{#if label}
-		<Label for={name}>{label}</Label>
+		<Label for={id}>{label}</Label>
 	{/if}
 
 	<!-- Hidden input stores currently selected value -->
 	<input
 		{name}
+		{id}
 		value={value?.value ?? ''}
 		class="hidden"
 		use:validate={validateOpts}
@@ -344,7 +351,7 @@
 	<!-- Error message if invalid -->
 	{#if invalidMessage}
 		<div class={['opacity-0 transition-opacity', !valid && 'opacity-100']}>
-			<Label for={name} error>{invalidMessage}</Label>
+			<Label for={id} error>{invalidMessage}</Label>
 		</div>
 	{/if}
 </div>