From 1251681cfdb2528477602c32194bdcac1f8314e9 Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <tobin@coblox.tech>
Date: Fri, 16 Oct 2020 12:42:47 +1100
Subject: [PATCH] Calculate amounts from BTC

---
 swap/src/alice.rs | 39 ++++++++++++++++++++++++++++++---------
 swap/src/lib.rs   |  8 ++++++--
 2 files changed, 36 insertions(+), 11 deletions(-)

diff --git a/swap/src/alice.rs b/swap/src/alice.rs
index 80ddc09c..aebd9b3f 100644
--- a/swap/src/alice.rs
+++ b/swap/src/alice.rs
@@ -13,7 +13,7 @@ mod messenger;
 
 use self::messenger::*;
 use crate::{
-    monero,
+    bitcoin, monero,
     network::{
         peer_tracker::{self, PeerTracker},
         request_response::{AliceToBob, TIMEOUT},
@@ -31,14 +31,8 @@ pub async fn swap(listen: Multiaddr) -> Result<()> {
         match swarm.next().await {
             BehaviourOutEvent::Request(messenger::BehaviourOutEvent::Btc { btc, channel }) => {
                 debug!("Got request from Bob to swap {}", btc);
-                let params = SwapParams {
-                    btc,
-                    // TODO: Do a real calculation.
-                    xmr: monero::Amount::from_piconero(10),
-                };
-
-                let msg = AliceToBob::Amounts(params);
-                swarm.send(channel, msg);
+                let p = calculate_amounts(btc);
+                swarm.send(channel, AliceToBob::Amounts(p));
             }
             other => panic!("unexpected event: {:?}", other),
         }
@@ -137,3 +131,30 @@ impl Default for Alice {
         }
     }
 }
+
+fn calculate_amounts(btc: bitcoin::Amount) -> SwapParams {
+    const XMR_PER_BTC: u64 = 100; // TODO: Get this from an exchange.
+
+    // XMR uses 12 zerose BTC uses 8.
+    let picos = (btc.as_sat() * 10000) * XMR_PER_BTC;
+    let xmr = monero::Amount::from_piconero(picos);
+
+    SwapParams { btc, xmr }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const ONE_BTC: u64 = 100_000_000;
+    const HUNDRED_XMR: u64 = 100_000_000_000_000;
+
+    #[test]
+    fn one_bitcoin_equals_a_hundred_moneroj() {
+        let btc = bitcoin::Amount::from_sat(ONE_BTC);
+        let want = monero::Amount::from_piconero(HUNDRED_XMR);
+
+        let SwapParams { xmr: got, .. } = calculate_amounts(btc);
+        assert_eq!(got, want);
+    }
+}
diff --git a/swap/src/lib.rs b/swap/src/lib.rs
index f9ba9a32..11f688d6 100644
--- a/swap/src/lib.rs
+++ b/swap/src/lib.rs
@@ -43,7 +43,7 @@ pub mod monero {
     use serde::{Deserialize, Serialize};
     use std::fmt;
 
-    #[derive(Copy, Clone, Debug, Serialize, Deserialize)]
+    #[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq)]
     pub struct Amount(u64);
 
     impl Amount {
@@ -76,7 +76,7 @@ pub mod bitcoin {
     use serde::{Deserialize, Serialize};
     use std::fmt;
 
-    #[derive(Copy, Clone, Debug, Serialize, Deserialize)]
+    #[derive(Copy, Clone, Debug, Serialize, Deserialize, PartialEq)]
     pub struct Amount(u64);
 
     impl Amount {
@@ -92,6 +92,10 @@ pub mod bitcoin {
         pub fn from_sat(satoshi: u64) -> Amount {
             Amount(satoshi)
         }
+
+        pub fn as_sat(&self) -> u64 {
+            self.0
+        }
     }
 
     impl fmt::Display for Amount {