<script lang="ts" generics="T">
  import { ChevronLeft, ChevronRight } from 'lucide-svelte';
  import type { Snippet } from 'svelte';

  let {
    items,
    item,
    ariaLabel
  }: {
    items: T[];
    item?: Snippet<[T, number]>;
    ariaLabel?: string;
  } = $props();

  let scroller: HTMLElement | undefined = $state();
  let scrollLeft = $state(0);
  let scrollWidth = $state(0);
  let clientWidth = $state(0);

  const atStart = $derived(scrollLeft <= 1);
  const atEnd   = $derived(scrollLeft + clientWidth >= scrollWidth - 1);

  function refreshMetrics() {
    if (!scroller) return;
    scrollLeft  = scroller.scrollLeft;
    scrollWidth = scroller.scrollWidth;
    clientWidth = scroller.clientWidth;
  }

  function page(direction: -1 | 1) {
    if (!scroller) return;
    const delta = direction * scroller.clientWidth * 0.85;
    scroller.scrollBy({ left: delta, behavior: 'smooth' });
    setTimeout(refreshMetrics, 350);
  }

  $effect(() => { refreshMetrics(); });
</script>

<div class="row relative" aria-label={ariaLabel}>
  <button
    type="button"
    class="arrow arrow-left"
    aria-label="Scroll left"
    onclick={() => page(-1)}
    disabled={atStart}
  >
    <ChevronLeft size={16} strokeWidth={1} />
  </button>

  <div
    bind:this={scroller}
    onscroll={refreshMetrics}
    data-testid="scroll-container"
    class="scroller flex gap-4 overflow-x-auto"
  >
    {#each items as it, i (i)}
      {@render item?.(it, i)}
    {/each}
  </div>

  <button
    type="button"
    class="arrow arrow-right"
    aria-label="Scroll right"
    onclick={() => page(1)}
    disabled={atEnd}
  >
    <ChevronRight size={16} strokeWidth={1} />
  </button>
</div>

<style>
  .row { padding: 0 36px; }
  .scroller {
    scroll-snap-type: x mandatory;
    scrollbar-width: thin;
  }
  .scroller > :global(*) {
    flex-shrink: 0;
    scroll-snap-align: start;
  }
  .arrow {
    position: absolute;
    top: 50%;
    transform: translateY(-50%);
    width: 32px;
    height: 32px;
    border-radius: 9999px;
    background: var(--fs-iron);
    color: var(--fs-vellum);
    display: flex;
    align-items: center;
    justify-content: center;
    border: 1px solid var(--fs-pewter);
    z-index: 1;
  }
  .arrow:hover:not(:disabled) { color: var(--fs-parchment); }
  .arrow:disabled { opacity: 0.3; cursor: not-allowed; }
  .arrow-left  { left: 0; }
  .arrow-right { right: 0; }
  @media (hover: hover) {
    .arrow { opacity: 0; transition: opacity 150ms ease; }
    .row:hover .arrow { opacity: 1; }
  }
</style>
