From e6ebe4c23c381862618b4246b3e2b3116b164ef0 Mon Sep 17 00:00:00 2001
From: Kasper Dissing Bargsteen <kb@concordium.com>
Date: Mon, 20 Mar 2023 15:49:11 +0100
Subject: [PATCH] Move `ExchangeRates` from concordium-std

---
 .../concordium-contracts-common/src/impls.rs  | 40 +++++++++++++++++++
 .../concordium-contracts-common/src/types.rs  | 31 ++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/smart-contracts/contracts-common/concordium-contracts-common/src/impls.rs b/smart-contracts/contracts-common/concordium-contracts-common/src/impls.rs
index 5c2df4194..321f6a673 100644
--- a/smart-contracts/contracts-common/concordium-contracts-common/src/impls.rs
+++ b/smart-contracts/contracts-common/concordium-contracts-common/src/impls.rs
@@ -301,6 +301,46 @@ impl Deserial for ExchangeRate {
     }
 }
 
+impl Serial for ExchangeRates {
+    fn serial<W: Write>(&self, out: &mut W) -> Result<(), W::Err> {
+        self.euro_per_energy.serial(out)?;
+        self.micro_ccd_per_euro.serial(out)?;
+        Ok(())
+    }
+}
+
+impl Deserial for ExchangeRates {
+    fn deserial<R: Read>(source: &mut R) -> ParseResult<Self> {
+        let bytes: [u8; 32] = source.read_array()?;
+        let chunks = unsafe { transmute::<[u8; 32], [[u8; 8]; 4]>(bytes) };
+
+        let euro_per_energy_numerator = u64::from_le_bytes(chunks[0]);
+        let euro_per_energy_denominator = u64::from_le_bytes(chunks[1]);
+        let micro_ccd_per_euro_numerator = u64::from_le_bytes(chunks[2]);
+        let micro_ccd_per_euro_denominator = u64::from_le_bytes(chunks[3]);
+
+        if euro_per_energy_numerator == 0
+            || euro_per_energy_denominator == 0
+            || micro_ccd_per_euro_numerator == 0
+            || micro_ccd_per_euro_denominator == 0
+        {
+            return Err(ParseError::default());
+        }
+
+        let euro_per_energy =
+            ExchangeRate::new_unchecked(euro_per_energy_numerator, euro_per_energy_denominator);
+        let micro_ccd_per_euro = ExchangeRate::new_unchecked(
+            micro_ccd_per_euro_numerator,
+            micro_ccd_per_euro_denominator,
+        );
+
+        Ok(Self {
+            euro_per_energy,
+            micro_ccd_per_euro,
+        })
+    }
+}
+
 impl Serial for ModuleReference {
     fn serial<W: Write>(&self, out: &mut W) -> Result<(), W::Err> { out.write_all(self.as_ref()) }
 }
diff --git a/smart-contracts/contracts-common/concordium-contracts-common/src/types.rs b/smart-contracts/contracts-common/concordium-contracts-common/src/types.rs
index 045b7c79c..7c596dd5c 100644
--- a/smart-contracts/contracts-common/concordium-contracts-common/src/types.rs
+++ b/smart-contracts/contracts-common/concordium-contracts-common/src/types.rs
@@ -1439,6 +1439,37 @@ impl ExchangeRate {
     pub fn denominator(&self) -> u64 { self.denominator }
 }
 
+/// The euro/NRG and microCCD/euro exchange rates.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ExchangeRates {
+    /// Euro per NRG exchange rate.
+    pub euro_per_energy:    ExchangeRate,
+    /// Micro CCD per Euro exchange rate.
+    pub micro_ccd_per_euro: ExchangeRate,
+}
+
+impl ExchangeRates {
+    /// Convert Euro cent to CCD using the current exchange rate.
+    /// This will round down to the nearest micro CCD.
+    pub fn convert_euro_cent_to_amount(&self, euro_cent: u64) -> Amount {
+        let numerator: u128 = self.micro_ccd_per_euro.numerator().into();
+        let denominator: u128 = self.micro_ccd_per_euro.denominator().into();
+        let euro_cent: u128 = euro_cent.into();
+        let result = numerator * euro_cent / (denominator * 100);
+        Amount::from_micro_ccd(result as u64)
+    }
+
+    /// Convert CCD to Euro cent using the current exchange rate.
+    /// This will round down to the nearest Euro cent.
+    pub fn convert_amount_to_euro_cent(&self, amount: Amount) -> u64 {
+        let numerator: u128 = self.micro_ccd_per_euro.numerator().into();
+        let denominator: u128 = self.micro_ccd_per_euro.denominator().into();
+        let micro_ccd: u128 = amount.micro_ccd().into();
+        let result = micro_ccd * 100 * denominator / numerator;
+        result as u64
+    }
+}
+
 /// Chain metadata accessible to both receive and init methods.
 #[cfg_attr(
     feature = "derive-serde",