frontend-svelte/src/widgets/SampleList/ui/SampleList/SampleList.svelte

<!--
    Component: SampleList
    Renders a list of fonts in a virtualized list to improve performance.
    - Includes pagination with auto-loading when scrolling near the bottom.
    - Provides a typography menu for font setup.
-->
<script lang="ts">
import {
    FontVirtualList,
    appliedFontsManager,
    createFontRowSizeResolver,
    fontStore,
} from '$entities/Font';
import { FontSampler } from '$features/DisplayFont';
import {
    TypographyMenu,
    typographySettingsStore,
} from '$features/SetupFont';
import { throttle } from '$shared/lib/utils';
import { Skeleton } from '$shared/ui';
import { layoutManager } from '../../model';

// FontSampler chrome heights — derived from Tailwind classes in FontSampler.svelte.
// Header: py-3 (12+12px padding) + ~32px content row ≈ 56px.
// Only the header is counted; the mobile footer (md:hidden) is excluded because
// on desktop, where container widths are wide and estimates matter most, it is invisible.
// Over-estimating chrome is safe (row is slightly taller than text needs, never cut off).
const SAMPLER_CHROME_HEIGHT = 56;

// p-4 = 16px per side = 32px total horizontal padding in FontSampler's content area.
// Using the smallest breakpoint (mobile) ensures contentWidth is never over-estimated:
// wider actual padding → more text wrapping → pretext height ≥ rendered height → safe.
const SAMPLER_CONTENT_PADDING_X = 32;

// Fallback row height used when the font has not loaded yet.
// Matches the previous hardcoded itemHeight={220} value to avoid regressions.
const SAMPLER_FALLBACK_HEIGHT = 220;

let text = $state('The quick brown fox jumps over the lazy dog...');
let wrapper = $state<HTMLDivElement | null>(null);
// Binds to the actual window height
let innerHeight = $state(0);
// Is the component above the middle of the viewport?
let isAboveMiddle = $state(false);
// Inner width of the wrapper div — updated by bind:clientWidth on mount and resize.
let containerWidth = $state(0);

const checkPosition = throttle(() => {
    if (!wrapper) return;

    const rect = wrapper.getBoundingClientRect();
    const viewportMiddle = innerHeight / 2;

    isAboveMiddle = rect.top < viewportMiddle;
}, 100);

// Resolver recreated when typography values change. The returned closure reads
// appliedFontsManager.statuses (a SvelteMap) on every call, so any font status
// change triggers a full offsets recompute in createVirtualizer — no DOM snap.
const fontRowHeight = $derived.by(() =>
    createFontRowSizeResolver({
        getFonts: () => fontStore.fonts,
        getWeight: () => typographySettingsStore.weight,
        getPreviewText: () => text,
        getContainerWidth: () => containerWidth,
        getFontSizePx: () => typographySettingsStore.renderedSize,
        getLineHeightPx: () => typographySettingsStore.height * typographySettingsStore.renderedSize,
        getStatus: key => appliedFontsManager.statuses.get(key),
        contentHorizontalPadding: SAMPLER_CONTENT_PADDING_X,
        chromeHeight: SAMPLER_CHROME_HEIGHT,
        fallbackHeight: SAMPLER_FALLBACK_HEIGHT,
    })
);
</script>

{#snippet skeleton()}
    <div class="flex flex-col gap-3 sm:gap-4 p-3 sm:p-4">
        {#each Array(5) as _, i}
            <div class="flex flex-col gap-1.5 sm:gap-2 p-3 sm:p-4 border rounded-lg sm:rounded-xl border-border-subtle bg-background-40">
                <div class="flex items-center justify-between mb-3 sm:mb-4">
                    <Skeleton class="h-6 sm:h-8 w-1/3" />
                    <Skeleton class="h-6 sm:h-8 w-6 sm:w-8 rounded-full" />
                </div>
                <Skeleton class="h-24 sm:h-32 w-full" />
            </div>
        {/each}
    </div>
{/snippet}

<svelte:window
    bind:innerHeight
    onscroll={checkPosition}
    onresize={checkPosition}
/>

<div bind:this={wrapper} bind:clientWidth={containerWidth}>
    <FontVirtualList
        itemHeight={fontRowHeight}
        useWindowScroll={true}
        weight={typographySettingsStore.weight}
        columns={layoutManager.columns}
        gap={layoutManager.gap}
        {skeleton}
    >
        {#snippet children({ item: font, index })}
            <FontSampler bind:text {font} {index} />
        {/snippet}
    </FontVirtualList>

    <TypographyMenu
        class="fixed bottom-4 sm:bottom-5 right-4 sm:left-1/2 sm:right-[unset] sm:-translate-x-1/2 z-50"
        hidden={!isAboveMiddle}
    />
</div>