feat(zoe): first transferable

packages/zoe/src/contracts/transferable-counter.js

@@ -0,0 +1,113 @@
+import { M } from '@endo/patterns';
+import { prepareExo, prepareExoClass } from '@agoric/vat-data';
+import { OfferHandlerI } from '../typeGuards.js';
+
+/** @typedef {import('@agoric/vat-data').Baggage} Baggage */
+
+const CounterDetails = harden({
+  count: M.bigint(),
+});
+
+const UseCounterI = M.interface('UseCounter', {
+  incr: M.call().returns(M.bigint()),
+  getDetails: M.call().returns(CounterDetails),
+  makeTransferInvitation: M.call().returns(M.promise()),
+});
+
+const ViewCounterI = M.interface('ViewCounter', {
+  view: M.call().returns(M.bigint()),
+});
+
+const TransferProposalShape = harden({
+  give: {},
+  want: {},
+  exit: {
+    onDemand: {},
+  },
+});
+
+/**
+ * @param {ZCF} zcf
+ * @param {{ count: bigint}} privateArgs
+ * @param {Baggage} instanceBaggage
+ */
+export const start = async (zcf, privateArgs, instanceBaggage) => {
+  const { count: startCount = 0n } = privateArgs;
+  assert.typeof(startCount, 'bigint');
+
+  // for use by upgraded versions.
+  const firstTime = !instanceBaggage.has('count');
+  if (firstTime) {
+    instanceBaggage.init('count', startCount);
+  }
+
+  let revokeUseCounter;
+
+  const makeUseCounter = prepareExoClass(
+    instanceBaggage,
+    'UseCounter',
+    UseCounterI,
+    count => {
+      assert(count === instanceBaggage.get('count'));
+      return harden({});
+    },
+    {
+      incr() {
+        const count = instanceBaggage.get('count') + 1n;
+        instanceBaggage.set(count);
+        return count;
+      },
+      getDetails() {
+        return harden({
+          count: instanceBaggage.get('count'),
+        });
+      },
+      makeTransferInvitation() {
+        const { self } = this;
+        const invitation = zcf.makeInvitation(
+          // eslint-disable-next-line no-use-before-define
+          transferHandler,
+          'transfer',
+          self.getDetails(),
+          TransferProposalShape,
+        );
+        revokeUseCounter(self);
+        return invitation;
+      },
+    },
+    {
+      getRevoker(revoke) {
+        revokeUseCounter = revoke;
+      },
+    },
+  );
+
+  const viewCounter = prepareExo(instanceBaggage, 'ViewCounter', ViewCounterI, {
+    view() {
+      return instanceBaggage.get('count');
+    },
+  });
+
+  const transferHandler = prepareExo(
+    instanceBaggage,
+    'TransferHandler',
+    OfferHandlerI,
+    {
+      /**
+       * @param {ZCFSeat} seat
+       */
+      handle(seat) {
+        const count = instanceBaggage.get('count');
+        // TODO assert(seat.getCustomDetails().count === count);
+        seat.exit();
+        return makeUseCounter(count);
+      },
+    },
+  );
+
+  return harden({
+    creatorFacet: makeUseCounter(startCount),
+    publicFacet: viewCounter,
+  });
+};
+harden(start);