Coin Flip

import { init } from "@zendfi/appkit";

const zend = init();
const me = await zend.identity.get();
let id = zend.launch.interaction;

// "Flip again" on a result card: start a new flip with the same people.
if (!id && zend.launch.start === "flip" && zend.launch.from) {
  const prev = await zend.interaction.get(zend.launch.from);
  const others = prev.participants
    .filter((p) => p.appUserId !== me.appUserId)
    .map((p) => p.appUserId);
  id = (await zend.interaction.create({ type: "flip", participants: others })).id;
}

async function flip() {
  const i = await zend.interaction.get(id);
  // Same order on both phones, so a draw of 0 or 1 names the same person for everyone.
  const people = [...i.participants].sort((a, b) => a.appUserId.localeCompare(b.appUserId));

  // Drawn by Zend and recorded once for this flip. Nobody can flip again until they like it.
  const r = await zend.random({ interactionId: id, label: "flip", kind: "int", n: 2 });
  const winner = people[r.value[0]].name;

  await zend.interaction.update(id, {
    state: "resolved",
    data: { winner, draw: { label: r.label, transactionId: r.transactionId } },
    idempotencyKey: `${id}:end`,
  });

  await zend.postCard({
    interactionId: id,
    template: "result",
    placement: "chat",
    idempotencyKey: `${id}:card`,
    slots: {
      title: `${winner} won the coin flip`,
      emoji: "🪙",
      check: true, // Zend shows "Result checked ✓" because the result came from a recorded draw
      buttons: [{ label: "Flip again", action: "start_interaction", type: "flip" }],
    },
  });

  setTimeout(() => zend.close({ winner }), 1500);
}