Empty state

EmptyPanel.tsxA closed union of the three kinds. The filtered kind names its filters, the zero carries its denominator.Copy

import { Button } from "@/components/ui/button";
import { Card } from "@/components/ui/card";

/**
 * Three kinds of nothing, as a closed union. A careless product renders them
 * identically, and they mean opposite things: one says the system is healthy,
 * one says you can't tell, one says nobody has wired this up yet. Each kind
 * carries the one thing its copy needs, so the panel cannot say "No data"
 * without saying which.
 */
export type Empty =
  /** Never received a sample. The next action is setup, not a filter. */
  | { kind: "never"; onConnect: () => void }
  /** Configured, but the query matched nothing. At least one filter, because the copy names them. */
  | { kind: "filtered"; filters: [string, ...string[]]; onClear: () => void }
  /** A real zero. It needs its denominator: zero out of two million is good news, zero out of zero is the first kind. */
  | { kind: "zero"; window: string; outOf: string };

const WORDS = ["no", "one", "two", "three", "four", "five"];
const count = (n: number, noun: string) => `${WORDS[n] ?? n} ${noun}${n === 1 ? "" : "s"}`;

export function EmptyPanel({ title, state }: { title: string; state: Empty }) {
  return (
    <Card className={`h-[150px] p-4 ${state.kind === "filtered" ? "border-2 border-chart-1" : ""}`}>
      <p className="text-[11px] uppercase tracking-wide text-muted-foreground">{title}</p>

      {state.kind === "never" && (
        <>
          <p className="mt-5 text-sm text-card-foreground">Nothing here yet</p>
          <p className="mt-1 text-[11px] text-muted-foreground">This panel has never received a sample.</p>
          <Button variant="outline" size="sm" className="mt-3 h-6 px-2 text-[10px]" onClick={state.onConnect}>connect a source</Button>
        </>
      )}

      {state.kind === "filtered" && (
        <>
          <p className="mt-5 text-sm text-card-foreground">No data</p>
          <p className="mt-1 text-[11px] text-muted-foreground">
            The query returned nothing for {state.filters.join(", ")}.
          </p>
          <Button variant="outline" size="sm" className="mt-3 h-6 px-2 text-[10px]" onClick={state.onClear}>
            clear {count(state.filters.length, "filter")}
          </Button>
        </>
      )}

      {state.kind === "zero" && (
        <>
          <p className="mt-4 text-4xl font-medium tabular-nums text-card-foreground">0</p>
          <p className="mt-2 text-[11px] tabular-nums text-muted-foreground">in the {state.window}, from {state.outOf}</p>
        </>
      )}
    </Card>
  );
}

demo.tsxHow it is called: the same panel in all three kinds. Clearing the filters turns the middle one into the real zero.Copy

import { useState } from "react";
import { EmptyPanel, type Empty } from "./EmptyPanel";

/**
 * The same panel three times, once per kind of empty. Clearing the two
 * filters on the middle one turns it into the real zero on the right, which
 * is the whole distinction: nothing matched, against nothing happened.
 */
export default function Demo() {
  const [middle, setMiddle] = useState<Empty>({
    kind: "filtered",
    filters: ["region = eu-west", "client = ios"],
    onClear: () => setMiddle({ kind: "zero", window: "last hour", outOf: "2.1M requests" }),
  });
  return (
    <div className="grid gap-5 sm:grid-cols-3">
      <EmptyPanel title="Checkout errors" state={{ kind: "never", onConnect: () => console.log("open the source picker") }} />
      <EmptyPanel title="Checkout errors" state={middle} />
      <EmptyPanel title="Checkout errors" state={{ kind: "zero", window: "last hour", outOf: "2.1M requests" }} />
    </div>
  );
}