From 003fb34971cf63466184351b4db5f7c67df4f444 Mon Sep 17 00:00:00 2001
From: Florian Dold <florian.dold@gmail.com>
Date: Fri, 24 Aug 2018 17:30:47 +0200
Subject: [PATCH] coinsim

---
 contrib/coinsim.ts | 152 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 152 insertions(+)
 create mode 100644 contrib/coinsim.ts

diff --git a/contrib/coinsim.ts b/contrib/coinsim.ts
new file mode 100644
index 000000000..9b8e12d2e
--- /dev/null
+++ b/contrib/coinsim.ts
@@ -0,0 +1,152 @@
+/*
+ This file is part of GNU Taler
+ (C) 2018 GNUnet e.V.
+
+ GNU Taler is free software; you can redistribute it and/or modify it under the
+ terms of the GNU General Public License as published by the Free Software
+ Foundation; either version 3, or (at your option) any later version.
+
+ GNU Taler is distributed in the hope that it will be useful, but WITHOUT ANY
+ WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+ A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+
+ You should have received a copy of the GNU General Public License along with
+ GNU Taler; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+ */
+
+
+function getRandomInt(min, max) {
+  return Math.floor(Math.random() * (max - min + 1)) + min;
+}
+
+const denoms = [512, 256, 128, 64, 32, 16, 8, 4, 2, 1];
+
+// mapping from denomination index to count
+const wallet = denoms.map(() => 0);
+
+const trans_max = 1000;
+const trans_min = 2;
+
+const withdraw_max = 5000;
+
+const num_transactions = parseInt(process.argv[2]);
+
+// Refresh or withdraw operations
+let ops = 0;
+
+function withdraw(amount) {
+  while (amount != 0) {
+    for (let i = 0; i < denoms.length; i++) {
+      let d = denoms[i];
+      if (d <= amount) {
+        amount -= d;
+        wallet[i]++;
+        ops++;
+        break;
+      }
+    }
+  }
+}
+
+function spendSmallestFirst(cost) {
+  while (cost != 0) {
+    for (let j = 0; j < denoms.length; j++) {
+      const k = denoms.length - j - 1;
+      const d = denoms[k];
+      const w = wallet[k];
+      if (w == 0) {
+        continue;
+      }
+      if (d <= cost) {
+        // spend
+        wallet[k]--;
+        cost -= d;
+        ops++;
+        break;
+      }
+      // partially spend and then refresh
+      ops++;
+      let r = d - cost;
+      wallet[k]--;
+      withdraw(r);
+      cost = 0;
+    }
+  }
+}
+
+function spendLargestFirst(cost) {
+  while (cost != 0) {
+    for (let j = 0; j < denoms.length; j++) {
+      const d = denoms[j];
+      const w = wallet[j];
+      if (w == 0) {
+        continue;
+      }
+      if (d <= cost) {
+        // spend
+        wallet[j]--;
+        cost -= d;
+        ops++;
+        break;
+      }
+      // partially spend and then refresh
+      ops++;
+      let r = d - cost;
+      wallet[j]--;
+      withdraw(r);
+      cost = 0;
+    }
+  }
+}
+
+function spendHybrid(cost) {
+    for (let j = 0; j < denoms.length; j++) {
+      const k = denoms.length - j - 1;
+      const d = denoms[k];
+      const w = wallet[k];
+      if (w == 0) {
+        continue;
+      }
+      if (d < cost) {
+        continue;
+      }
+      // partially spend and then refresh
+      ops++;
+      let r = d - cost;
+      wallet[k]--;
+      withdraw(r);
+      cost = 0;
+    }
+
+  spendSmallestFirst(cost);
+}
+
+for (let i = 0; i < num_transactions; i++) {
+  // check existing wallet balance
+  let balance = 0;
+  for (let j = 0; j < denoms.length; j++) {
+    balance += wallet[j] * denoms[j]
+  }
+  // choose how much we want to spend
+  let cost = getRandomInt(trans_min, trans_max);
+  if (balance < cost) {
+    // we need to withdraw
+    let amount = getRandomInt(cost - balance, withdraw_max);
+    withdraw(amount);
+  }
+
+  // check that we now have enough balance
+  balance = 0;
+  for (let j = 0; j < denoms.length; j++) {
+    balance += wallet[j] * denoms[j]
+  }
+
+  if (balance < cost) {
+    throw Error("not enough balance");
+  }
+
+  // now we spend
+  spendHybrid(cost);
+}
+
+console.log(ops / num_transactions);