Two-pane list and detail

Working through a queue with the list and the item visible at once. Keyboard movement through the list is what makes it a queue rather than a pair of panels.

npx shadcn@latest add button

Tokens this needs: --card, --card-foreground, --muted, --muted-foreground, --border, --ring, --chart-1

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// ListDetail.tsx
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import { useState, type KeyboardEvent } from "react";
import { Button } from "@/components/ui/button";
import { cn } from "@/lib/utils";
import { Sparkline } from "../sparkline/Sparkline";

export type Item = {
  id: string;
  title: string;
  /** The second line in the list: count and age. */
  meta: string;
  /** Events over the window, drawn in the detail pane. */
  events: number[];
  stats: [label: string, value: string][];
  body: string;
  /** The full-width view this pane hands over to when the content is wider
   *  than the pane. */
  href: string;
};

type Props = {
  items: Item[];
  /** Arrived since the list was drawn. Held behind the "n new" chip until
   *  asked for, because a queue that inserts under someone makes them skip. */
  incoming: Item[];
  onReveal: () => void;
  defaultSelectedId?: string;
  onSelect?: (id: string) => void;
};

export function ListDetail({ items, incoming, onReveal, defaultSelectedId, onSelect }: Props) {
  const [selectedId, setSelectedId] = useState(defaultSelectedId ?? items[0]?.id);
  const index = Math.max(0, items.findIndex((i) => i.id === selectedId));
  const item = items[index];
  const select = (i: number) => {
    const next = items[Math.min(items.length - 1, Math.max(0, i))];
    if (!next) return;
    setSelectedId(next.id);
    onSelect?.(next.id);
  };
  // Up and down through the list, detail following. This is the whole
  // productivity argument, so it lives on the list rather than on a shortcut.
  const onKeyDown = (e: KeyboardEvent<HTMLUListElement>) => {
    if (e.key === "ArrowDown") { e.preventDefault(); select(index + 1); }
    if (e.key === "ArrowUp") { e.preventDefault(); select(index - 1); }
  };

  return (
    <div className="grid grid-cols-[0.8fr_1.4fr] gap-4">
      <div className="overflow-hidden rounded-lg border bg-card">
        {incoming.length > 0 && (
          <Button variant="ghost" onClick={onReveal} className="h-auto w-full justify-start gap-2 rounded-none border-b bg-chart-1/10 px-3 py-1.5 text-[11px] text-chart-1 hover:bg-chart-1/20 hover:text-chart-1">
            <span className="size-1.5 rounded-full bg-chart-1" />
            {incoming.length} new
          </Button>
        )}
        <ul className="divide-y outline-none focus-visible:ring-1 focus-visible:ring-ring" tabIndex={0} role="listbox" aria-activedescendant={item?.id} onKeyDown={onKeyDown}>
          {items.map((i, n) => (
            <li
              key={i.id}
              id={i.id}
              role="option"
              aria-selected={n === index}
              onClick={() => select(n)}
              className={cn("cursor-pointer px-3 py-2 text-[11px]", n === index ? "bg-muted/60 text-card-foreground" : "text-muted-foreground")}
            >
              <p className="truncate">{i.title}</p>
              <p className="truncate text-[10px] text-muted-foreground">{i.meta}</p>
            </li>
          ))}
        </ul>
      </div>

      {item && (
        <div className="rounded-lg border bg-muted p-4">
          <p className="border-b pb-2 text-sm text-card-foreground">{item.title}</p>
          <div className="mt-3 grid grid-cols-2 gap-3">
            <div className="rounded border bg-card p-2 text-muted-foreground">
              <p className="text-[10px]">events, last hour</p>
              <Sparkline values={item.events} width={150} height={24} />
            </div>
            <dl className="rounded border bg-card p-2 text-[10px]">
              {item.stats.map(([label, value]) => (
                <div key={label} className="flex justify-between gap-2">
                  <dt className="text-muted-foreground">{label}</dt>
                  <dd className="tabular-nums text-card-foreground">{value}</dd>
                </div>
              ))}
            </dl>
          </div>
          <p className="mt-3 font-mono text-[10px] leading-relaxed text-card-foreground">{item.body}</p>
          <div className="mt-4 flex items-center gap-3 border-t pt-2.5 text-[10px] text-muted-foreground">
            <kbd className="rounded border px-1.5 py-0.5">↑</kbd><kbd className="rounded border px-1.5 py-0.5">↓</kbd>
            <span>move the selection</span>
            <a className="ml-auto rounded border px-2 py-0.5 text-card-foreground" href={item.href}>full page</a>
          </div>
        </div>
      )}
    </div>
  );
}

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// demo.tsx
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import { useState } from "react";
import { ListDetail, type Item } from "./ListDetail";

const alert = (id: string, title: string, meta: string, events: number[], users: number, body: string): Item => ({
  id, title, meta, events, body, href: `/issues/${id}`,
  stats: [["first seen", "3d ago"], ["last seen", meta.split(" · ")[1]], ["users", String(users)]],
});

const QUEUE: Item[] = [
  alert("i-4182", "ConnectionReset · payments-worker", "8 events · 11m ago", [1, 0, 2, 1, 3, 1], 6, "ConnectionResetError: [Errno 104] Connection reset by peer at psycopg2.connect (worker.py:88)"),
  alert("i-4183", "TimeoutError · checkout-api", "142 events · 2m ago", [6, 9, 8, 19, 24, 31, 45], 412, "TimeoutError: request to inventory-svc exceeded 3000ms at fetchStock (checkout/cart.ts:214), retried 2 times, gave up"),
  alert("i-4179", "NullPointerException · catalog-svc", "3 events · 26m ago", [1, 1, 0, 0, 1, 0], 3, "java.lang.NullPointerException: product.variants is null at CatalogMapper.toDto (CatalogMapper.java:57)"),
  alert("i-4175", "RateLimitExceeded · search-api", "51 events · 40m ago", [12, 14, 9, 8, 5, 3], 51, "RateLimitExceeded: 429 from provider after 1,000 req/min at SearchClient.query (search.ts:41)"),
  alert("i-4171", "DeadlineExceeded · notifications", "12 events · 1h ago", [4, 3, 2, 2, 1, 0], 12, "DeadlineExceeded: push delivery took 12.4s, budget 10s at Dispatcher.send (dispatch.go:133)"),
];

const INCOMING: Item[] = [
  alert("i-4184", "TimeoutError · checkout-api", "9 events · 1m ago", [2, 3, 4], 9, "TimeoutError: request to pricing-svc exceeded 3000ms at fetchQuote (checkout/quote.ts:72)"),
  alert("i-4185", "ECONNREFUSED · image-resizer", "2 events · 1m ago", [1, 1], 2, "Error: connect ECONNREFUSED 10.0.4.12:9000 at TCPConnectWrap.afterConnect (net.js:1148)"),
  alert("i-4186", "ValidationError · signup-api", "1 event · now", [1], 1, "ValidationError: email must be a valid address at SignupSchema.parse (signup.ts:19)"),
];

/**
 * Five issues with the second selected and three more waiting behind the
 * chip. Arrow keys walk the list once it has focus; the chip merges the
 * three in at the top, and only then.
 */
export default function Demo() {
  const [items, setItems] = useState(QUEUE);
  const [incoming, setIncoming] = useState(INCOMING);
  const reveal = () => {
    setItems([...incoming, ...items]);
    setIncoming([]);
  };
  return <ListDetail items={items} incoming={incoming} onReveal={reveal} defaultSelectedId="i-4183" />;
}