From 994de053ff0cd8aebe367d6ba89d75a34df4b778 Mon Sep 17 00:00:00 2001
From: Stanislav Pirx <stanislav.pirx@gmail.com>
Date: Sun, 14 Nov 2021 19:36:29 +0300
Subject: [PATCH] fix redeeming zero aUST

Signed-off-by: Stanislav Pirx <stanislav.pirx@gmail.com>
---
 artifacts/basset_vault_basset_vault.wasm | Bin 466430 -> 466447 bytes
 artifacts/checksums.txt                  |   2 +-
 contracts/basset_vault/src/utils.rs      | 139 +++++++++++++++++++++--
 3 files changed, 133 insertions(+), 8 deletions(-)

diff --git a/artifacts/basset_vault_basset_vault.wasm b/artifacts/basset_vault_basset_vault.wasm
index 9235e32686ee1a546ec40cc7a04855db4c5c6af7..0a02217def9c1b9aed0537fdff77fdb432180094 100644
GIT binary patch
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diff --git a/artifacts/checksums.txt b/artifacts/checksums.txt
index a962b6a..e54e316 100644
--- a/artifacts/checksums.txt
+++ b/artifacts/checksums.txt
@@ -1,4 +1,4 @@
-3e90ee3bae93d3593e5c05aa955ec4724a87491833275f8c6f117b2d19655490  basset_vault_basset_vault.wasm
+6c48277bb8224903af5285c8adcae2d37aa85165b2851dd0be463ef6680ecaaf  basset_vault_basset_vault.wasm
 30ead7593851977b5279282ad2c60e8d899e5232d836dd1c311bd5bce45f817b  basset_vault_basset_vault_strategy.wasm
 5b24d8945b6884c49196cf7626e82a5f25f71f4b722594349774d8998f4252c5  basset_vault_nasset_config_holder.wasm
 5b6ba6875a09342fc2f8c4bcb3095197e30d0f5b200743c4dad8e5bcb99f622f  basset_vault_nasset_rewards.wasm
diff --git a/contracts/basset_vault/src/utils.rs b/contracts/basset_vault/src/utils.rs
index 87ae7df..adeff27 100644
--- a/contracts/basset_vault/src/utils.rs
+++ b/contracts/basset_vault/src/utils.rs
@@ -172,7 +172,11 @@ pub fn get_repay_loan_action(
     //on first try only selling aterra, cause with high probability we will repay loan
     //in 'reply' handler, so don't need to do that twice
     if is_first_try || repay_amount.is_zero() {
-        if aterra_value.is_zero() {
+        if aterra_value.is_zero() && repay_amount.is_zero() {
+            //impossible case, cause conditions already captured by code above, but for
+            //clarification I leave it
+            return RepayLoanAction::Nothing;
+        } else if aterra_value.is_zero() {
             return RepayLoanAction::RepayLoan {
                 amount: repay_amount,
             };
@@ -181,11 +185,17 @@ pub fn get_repay_loan_action(
 
             let aterra_to_sell =
                 tax_info.append_tax(stables_from_aterra_sell) / aterra_exchange_rate;
+
             //make sure that we do not redeem more then we have (in case if some issue with tax precision)
             let aterra_to_sell = aterra_to_sell.min(aterra_balance);
-            return RepayLoanAction::SellAterra {
-                amount: aterra_to_sell,
-            };
+
+            if aterra_to_sell.is_zero() {
+                return RepayLoanAction::Nothing;
+            } else {
+                return RepayLoanAction::SellAterra {
+                    amount: aterra_to_sell,
+                };
+            }
         }
     }
 
@@ -214,9 +224,16 @@ pub fn get_repay_loan_action(
             let aterra_to_sell = tax_info.append_tax(bounded_aterra_value) / aterra_exchange_rate;
             //make sure that we do not redeem more then we have (in case if some issue with tax precision)
             let aterra_to_sell = aterra_to_sell.min(aterra_balance);
-            RepayLoanAction::RepayLoanAndSellAterra {
-                aterra_amount_to_sell: aterra_to_sell,
-                repay_loan_amount: repay_amount,
+
+            if aterra_to_sell.is_zero() {
+                return RepayLoanAction::RepayLoan {
+                    amount: repay_amount,
+                };
+            } else {
+                RepayLoanAction::RepayLoanAndSellAterra {
+                    aterra_amount_to_sell: aterra_to_sell,
+                    repay_loan_amount: repay_amount,
+                }
             }
         }
     }
@@ -1186,6 +1203,114 @@ mod test {
         );
     }
 
+    #[test]
+    fn get_repay_loan_action_first_try_but_we_cant_repay_any_loan_cause_aterra_is_zero() {
+        let aterra_balance = Uint256::zero();
+        let stable_coin_balance = Uint256::zero();
+        let aterra_exchange_rate = Decimal256::from_str("1.2").unwrap();
+        let repay_amount = Uint256::from(1_000u64);
+        let aim_buffer_size = Uint256::from(100u64);
+        let tax_info = TaxInfo {
+            rate: Decimal256::zero(),
+            cap: Uint256::zero(),
+        };
+        let repay_action = get_repay_loan_action(
+            stable_coin_balance,
+            aterra_balance,
+            aterra_exchange_rate,
+            repay_amount,
+            aim_buffer_size,
+            &tax_info,
+            true,
+        );
+        assert_eq!(RepayLoanAction::Nothing, repay_action);
+    }
+
+    #[test]
+    fn get_repay_loan_action_first_try_but_we_cant_repay_any_loan_cause_cant_sell_zero_aterra() {
+        let aterra_balance = Uint256::one();
+        let stable_coin_balance = Uint256::zero();
+        let aterra_exchange_rate = Decimal256::from_str("1.2").unwrap();
+        let repay_amount = Uint256::from(1_000u64);
+        let aim_buffer_size = Uint256::from(100u64);
+        let tax_info = TaxInfo {
+            rate: Decimal256::zero(),
+            cap: Uint256::zero(),
+        };
+        let repay_action = get_repay_loan_action(
+            stable_coin_balance,
+            aterra_balance,
+            aterra_exchange_rate,
+            repay_amount,
+            aim_buffer_size,
+            &tax_info,
+            true,
+        );
+        assert_eq!(RepayLoanAction::Nothing, repay_action);
+    }
+
+    #[allow(non_snake_case)]
+    #[test]
+    fn get_repay_loan_action_sell_aterra_with_super_low_amount__nothing_as_result() {
+        let aterra_balance = Uint256::from(1_000u64);
+        let aterra_exchange_rate = Decimal256::from_str("1.2").unwrap();
+        let stable_coin_balance = Uint256::from(1_000u64);
+        let repay_amount = Uint256::zero();
+        let aim_buffer_size = stable_coin_balance + Uint256::one();
+        let tax_info = TaxInfo {
+            rate: Decimal256::zero(),
+            cap: Uint256::zero(),
+        };
+        let repay_action = get_repay_loan_action(
+            stable_coin_balance,
+            aterra_balance,
+            aterra_exchange_rate,
+            repay_amount,
+            aim_buffer_size,
+            &tax_info,
+            false,
+        );
+        // aim_buffer_size is stable_coin_balance + 1
+        // but aUST rate is 1.2, and 1/1.2 = 0
+        // and we cant sell 0 aUST, means - do Nothing
+        assert_eq!(RepayLoanAction::Nothing, repay_action);
+    }
+
+    #[allow(non_snake_case)]
+    #[test]
+    fn get_repay_loan_action_repay_loan_and_sell_aterra_super_low_amount__repay_loan_as_result() {
+        let aterra_balance = Uint256::from(300_000u64);
+        let aterra_exchange_rate = Decimal256::from_str("1.25").unwrap();
+        let stable_coin_balance = Uint256::from(100_000u64);
+        let repay_amount = Uint256::from(100_000u64);
+        let aim_buffer_size = Uint256::from(1u64);
+        let tax_info = TaxInfo {
+            rate: Decimal256::zero(),
+            cap: Uint256::zero(),
+        };
+        let repay_action = get_repay_loan_action(
+            stable_coin_balance,
+            aterra_balance,
+            aterra_exchange_rate,
+            repay_amount,
+            aim_buffer_size,
+            &tax_info,
+            false,
+        );
+        assert_eq!(
+            //need to repay: 100k
+            //stable_coin_balance: 100k
+            //stables_after_repaying: 100k - 100k = 0
+            //total_stables_needed = aim_buffer_size = 1
+            //means we need to sell aUST to get 1: 1/1.25 = 0
+            //we cant sell 0 aUST, means just RepayLoan, without selling aUST
+            RepayLoanAction::RepayLoan {
+                amount: Uint256::from(100_000u64), //minus 750 tax cap
+            },
+            repay_action
+        );
+    }
+
     #[test]
     fn calc_wanted_stablecoins_1() {
         let stable_coin_balance = Uint256::zero();