wallet-core: Add function to sum the balance for phoenix notes

Resolves #2117

wallet-core/Cargo.toml

@@ -12,5 +12,7 @@ rand_chacha = { version = "0.3", default-features = false }
 sha2 = { version = "0.10", default-features = false }
 
 [dev-dependencies]
+rand = "0.8"
+ff = { version = "0.13", default-features = false }
 
 [features]

wallet-core/src/lib.rs

@@ -4,14 +4,54 @@
 //
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
-//! Types used for interacting with Dusk's transfer and stake contracts.
+//! Implementations of basic wallet functionalities.
 
 #![cfg_attr(target_family = "wasm", no_std)]
 #![deny(missing_docs)]
 #![deny(rustdoc::broken_intra_doc_links)]
 #![deny(clippy::pedantic)]
 
+extern crate alloc;
+
 pub mod keys;
 
 /// Length of the seed of the generated rng.
 pub const RNG_SEED: usize = 64;
+
+// The maximum amount of input notes that can be spend in one
+// phoenix-transaction
+const MAX_INPUT_NOTES: usize = 4;
+
+use alloc::vec::Vec;
+
+use execution_core::transfer::phoenix::{Note, ViewKey as PhoenixViewKey};
+
+/// Calculate the sum for all the given [`Note`]s that belong to the given
+/// [`PhoenixViewKey`].
+pub fn phoenix_balance(
+    phoenix_vk: &PhoenixViewKey,
+    notes: impl AsRef<[Note]>,
+) -> BalanceInfo {
+    let mut values: Vec<u64> = Vec::new();
+    notes.as_ref().iter().for_each(|note| {
+        values.push(note.value(Some(phoenix_vk)).unwrap_or_default())
+    });
+
+    values.sort_by(|a, b| b.cmp(a));
+
+    BalanceInfo {
+        value: values.iter().sum(),
+        spendable: values[..MAX_INPUT_NOTES].iter().sum(),
+    }
+}
+
+/// Information about the balance of a particular key.
+#[derive(Debug, Default, Hash, Clone, Copy, PartialEq, Eq)]
+pub struct BalanceInfo {
+    /// The total value of the balance.
+    pub value: u64,
+    /// The maximum _spendable_ value in a single transaction. This is
+    /// different from `value` since there is a maximum number of notes one can
+    /// spend.
+    pub spendable: u64,
+}

wallet-core/tests/balance.rs

@@ -0,0 +1,72 @@
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this
+// file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+// Copyright (c) DUSK NETWORK. All rights reserved.
+
+use ff::Field;
+use rand::rngs::StdRng;
+use rand::SeedableRng;
+
+use execution_core::{
+    transfer::phoenix::{
+        Note, PublicKey as PhoenixPublicKey, SecretKey as PhoenixSecretKey,
+    },
+    JubJubScalar,
+};
+
+use wallet_core::{phoenix_balance, BalanceInfo};
+
+#[test]
+fn test_balance() {
+    let mut rng = StdRng::seed_from_u64(0xdab);
+
+    let owner_sk = PhoenixSecretKey::random(&mut rng);
+    let owner_pk = PhoenixPublicKey::from(&owner_sk);
+    let sender_pk = PhoenixPublicKey::from(&PhoenixSecretKey::random(&mut rng));
+
+    let mut notes = Vec::new();
+
+    // create the notes
+    for value in 0..=10 {
+        let value_blinder = JubJubScalar::random(&mut rng);
+        let sender_blinder = [
+            JubJubScalar::random(&mut rng),
+            JubJubScalar::random(&mut rng),
+        ];
+
+        // we want to test with a mix of transparent and obfuscated notes so we
+        // make every 10th note transparent
+        let note = if value % 10 == 0 {
+            Note::transparent(
+                &mut rng,
+                &sender_pk,
+                &owner_pk,
+                value,
+                sender_blinder,
+            )
+        } else {
+            Note::obfuscated(
+                &mut rng,
+                &sender_pk,
+                &owner_pk,
+                value,
+                value_blinder,
+                sender_blinder,
+            )
+        };
+        notes.push(note);
+    }
+
+    // the sum of these notes should be 5 * 11 = 55
+    // and the spendable notes are 7 + 8 + 9 + 10 = 34
+    let expected_balance = BalanceInfo {
+        value: 55,
+        spendable: 34,
+    };
+
+    assert_eq!(
+        phoenix_balance(&(&owner_sk).into(), notes),
+        expected_balance
+    );
+}

wallet-core/tests/keys_derive.rs → wallet-core/tests/keys.rs

@@ -5,6 +5,7 @@
 // Copyright (c) DUSK NETWORK. All rights reserved.
 
 use dusk_bytes::Serializable;
+
 use wallet_core::keys::{
     derive_bls_sk, derive_phoenix_pk, derive_phoenix_sk, derive_phoenix_vk,
 };