Command menu

Two trigger characters doing two jobs. Slash opens verbs the product can execute; at-sign opens objects filtered by what the viewer is allowed to see. Both stay invisible until typed, which is what keeps them out of the way.

npx shadcn@latest add command
npm i cmdk

Tokens this needs: --background, --popover, --popover-foreground, --accent, --accent-foreground, --muted-foreground, --border, --chart-1

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// CommandMenu.tsx
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import { useRef, useState, type KeyboardEvent } from "react";
import { Command, CommandEmpty, CommandGroup, CommandItem, CommandList } from "@/components/ui/command";

/**
 * Two triggers, two jobs. A verb is a code path the product runs; an object is
 * a reference the prompt carries. They are separate lists with separate
 * handlers so the two never blur into one menu.
 */
export type Verb = { name: string };
export type Ref = { id: string; name: string };
/** The prompt is tokens rather than a string, so a mention stays a reference
 *  instead of decaying back into prose the model has to resolve. */
export type Token = { kind: "text"; text: string } | { kind: "mention"; ref: Ref };

type Props = {
  value: Token[];
  onChange: (value: Token[]) => void;
  verbs: Verb[];
  objects: Ref[];
  /** The picker reveals what exists, so it cannot mount without a permission
   *  filter. Pass the viewer's real check, never `() => true` in production. */
  canSee: (ref: Ref) => boolean;
  onCommand: (verb: Verb, prompt: Token[]) => void;
  onSend: (prompt: Token[]) => void;
};

/** A trigger counts at the start of the text or after a space. "3/4" and
 *  "mail@host" are ordinary typing and open nothing. */
const TRIGGER = /(?:^|\s)([/@])([^\s/@]*)$/;

export function CommandMenu({ value, onChange, verbs, objects, canSee, onCommand, onSend }: Props) {
  const listRef = useRef<HTMLDivElement>(null);
  // The trailing token is what the input edits; everything before it is set.
  const head = value.slice(0, -1);
  const tail = value[value.length - 1];
  const text = tail?.kind === "text" ? tail.text : "";
  const match = TRIGGER.exec(text);
  // Escape remembers where the trigger was, so the menu stays shut until a
  // new one is typed. The character itself is left in place.
  const [dismissed, setDismissed] = useState<number | null>(null);
  const at = match ? text.length - match[0].length + (match[0].length - match[1].length - match[2].length) : -1;
  const open = !!match && dismissed !== at;
  const mode = match?.[1] === "/" ? "verbs" : "objects";
  const query = (match?.[2] ?? "").toLowerCase();

  const setText = (t: string) => onChange([...head, { kind: "text", text: t }]);
  const beforeTrigger = () => text.slice(0, at);

  const pickVerb = (v: Verb) => {
    onCommand(v, [...head, { kind: "text", text: beforeTrigger() }]);
    setText(beforeTrigger());
  };
  const pickObject = (r: Ref) =>
    onChange([...head, { kind: "text", text: beforeTrigger() }, { kind: "mention", ref: r }, { kind: "text", text: " " }]);

  const onKeyDown = (e: KeyboardEvent<HTMLInputElement>) => {
    if (open && e.key === "Escape") { e.preventDefault(); setDismissed(at); return; }
    // The list owns arrow keys and Enter while it is open; focus stays here.
    if (open && ["ArrowUp", "ArrowDown", "Enter"].includes(e.key)) {
      e.preventDefault();
      listRef.current?.dispatchEvent(new KeyboardEvent("keydown", { key: e.key, bubbles: true }));
      return;
    }
    if (e.key === "Enter") { e.preventDefault(); onSend(value); return; }
    if (e.key === "Backspace" && text === "" && head.length) { e.preventDefault(); onChange(head.slice(0, -1)); }
  };

  return (
    <div className="relative">
      {open && (
        <Command ref={listRef} shouldFilter={false} className="absolute bottom-full mb-1 w-72 rounded-lg border shadow-md">
          <CommandList id="command-menu-list">
            <CommandEmpty>Nothing matches</CommandEmpty>
            {mode === "verbs" ? (
              <CommandGroup heading="/ verbs">
                {verbs.filter((v) => v.name.toLowerCase().startsWith(query)).map((v) => (
                  <CommandItem key={v.name} value={v.name} onSelect={() => pickVerb(v)}>
                    {v.name}
                  </CommandItem>
                ))}
              </CommandGroup>
            ) : (
              <CommandGroup heading="@ objects">
                {objects.filter(canSee).filter((r) => r.name.toLowerCase().includes(query)).map((r) => (
                  <CommandItem key={r.id} value={r.id} onSelect={() => pickObject(r)}>{r.name}</CommandItem>
                ))}
              </CommandGroup>
            )}
          </CommandList>
        </Command>
      )}

      <div className="flex flex-wrap items-center gap-1 rounded-lg border bg-background px-3 py-2 text-sm">
        {head.map((t, i) =>
          t.kind === "text" ? (
            <span key={i} className="whitespace-pre">{t.text}</span>
          ) : (
            <span key={i} className="rounded-md bg-chart-1/15 px-1.5 py-0.5 text-xs text-chart-1">@{t.ref.name}</span>
          ),
        )}
        <input
          value={text}
          onChange={(e) => setText(e.target.value)}
          onKeyDown={onKeyDown}
          aria-label="Message"
          aria-expanded={open}
          role="combobox"
          aria-controls="command-menu-list"
          placeholder={head.length ? "" : "Message. / for actions, @ for pages and people"}
          className="min-w-[8rem] flex-1 bg-transparent outline-none placeholder:text-muted-foreground"
        />
      </div>
    </div>
  );
}

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// demo.tsx
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import { useState } from "react";
import { CommandMenu, type Token, type Verb } from "./CommandMenu";

/**
 * Opens on the slash. The prompt already carries one mention, picked with @,
 * and the viewer is mid-way through typing a verb. Picking a verb runs it and
 * clears the trigger; picking an object drops a chip into the prompt.
 */
const VERBS: Verb[] = [{ name: "summarise" }, { name: "translate" }];
const OBJECTS = [
  { id: "doc-q3", name: "Q3 forecast", team: "finance" },
  { id: "doc-rivera", name: "Rivera account brief", team: "sales" },
  { id: "doc-comp", name: "Compensation bands", team: "people" },
];
const VIEWER_TEAMS = new Set(["finance", "sales"]);

export default function Demo() {
  const [prompt, setPrompt] = useState<Token[]>([
    { kind: "text", text: "Compare " },
    { kind: "mention", ref: { id: "doc-q3", name: "Q3 forecast" } },
    { kind: "text", text: " with /" },
  ]);
  const [ran, setRan] = useState<string | null>(null);

  return (
    <div className="pt-28">
      <CommandMenu
        value={prompt}
        onChange={setPrompt}
        verbs={VERBS}
        objects={OBJECTS}
        canSee={(r) => VIEWER_TEAMS.has(OBJECTS.find((o) => o.id === r.id)?.team ?? "")}
        onCommand={(v) => setRan(v.name)}
        onSend={() => setRan("sent")}
      />
      {ran && <p className="mt-2 text-xs text-muted-foreground">ran /{ran}</p>}
    </div>
  );
}