wip: Add loop iteration limit

src/lib.rs

@@ -151,8 +151,19 @@ pub fn select_coins_bnb(
     _fee_rate: FeeRate,
     weighted_utxos: &mut [WeightedUtxo],
 ) -> Option<Vec<WeightedUtxo>> {
+    // Total_Tries in Core:
+    // https://github.com/bitcoin/bitcoin/blob/1d9da8da309d1dbf9aef15eb8dc43b4a2dc3d309/src/wallet/coinselection.cpp#L74
+    const ITERATION_LIMIT: i32 = 100_000;
+
+    let mut iteration = 0;
+    let mut index = 0;
+    let mut backtrack;
+
     let mut value = Amount::ZERO;
+    let waste = Amount::MAX_MONEY;
+
     let mut selection: Vec<WeightedUtxo> = vec![];
+    let mut best_selection: Vec<WeightedUtxo> = vec![];
     let available_value: Amount = weighted_utxos.iter().map(|u| u.utxo.value).sum();
 
     if available_value < target {
@@ -161,29 +172,67 @@ pub fn select_coins_bnb(
 
     weighted_utxos.sort_by(|a, b| b.utxo.value.cmp(&a.utxo.value));
 
-    for (_i, utxo) in weighted_utxos.iter().enumerate() {
+    while iteration < ITERATION_LIMIT {
+        backtrack = false;
+
         // backtrack
         //
         // There are three conditions for backtracking:
         //
-        // * value meets or exceeded target
-        // * leaf node (nothing left to explorer)
-        // * not enough value to make it to target
-        if value >= target
-            || available_value + value < target
-            || utxo == weighted_utxos.last().unwrap()
-        {
-            // backtrack
+        // * value meets or exceeded target.
+        // * leaf node (nothing left to explorer).
+        // * not enough value to make it to target.
+
+        // value meets or exceeds the target:
+        //
+        // For example:
+        //      o
+        //     /
+        //    4
+        //   /
+        //  3
+        //
+        // Transform to:
+        //      o
+        //     /
+        //    4
+        //   / \
+        //      3
+        if value >= target {
+            backtrack = true;
+            let current_waste = value - target;
+
+            if current_waste <= waste {
+                best_selection = selection.clone();
+                selection.pop();
+            }
+
+            index -= 1;
         }
 
+        //if index == selection.len() {
+        //}
+
+        //if available_value + value < target {
+        //}
+
+        if backtrack {
+            if selection.is_empty() {
+                return Some(best_selection);
+            }
+        }
         // proceed with depth first search.
         else {
+            let utxo = &weighted_utxos[index];
             selection.push(utxo.clone());
             value += utxo.utxo.value;
         }
+
+        index += 1;
+        iteration += 1;
     }
 
-    Some(selection)
+    Some(best_selection)
 }
 
 #[cfg(test)]
@@ -216,17 +265,82 @@ mod tests {
             },
         };
 
-        vec![utxo_one, utxo_two]
+        let utxo_three = WeightedUtxo {
+            satisfaction_weight: SATISFACTION_SIZE,
+            utxo: TxOut {
+                value: Amount::from_str("3 cBTC").unwrap(),
+                script_pubkey: ScriptBuf::new(),
+            },
+        };
+
+        let utxo_four = WeightedUtxo {
+            satisfaction_weight: SATISFACTION_SIZE,
+            utxo: TxOut {
+                value: Amount::from_str("4 cBTC").unwrap(),
+                script_pubkey: ScriptBuf::new(),
+            },
+        };
+
+        vec![utxo_one, utxo_two, utxo_three, utxo_four]
+    }
+
+    #[test]
+    fn one_solution_one_coin() {
+        let target = Amount::from_str("1 cBTC").unwrap();
+
+        let mut weighted_utxos = vec![WeightedUtxo {
+            satisfaction_weight: SATISFACTION_SIZE,
+            utxo: TxOut {
+                value: Amount::from_str("1 cBTC").unwrap(),
+                script_pubkey: ScriptBuf::new(),
+            },
+        }];
+
+        let utxo_match = select_coins_bnb(target, FEE_RATE, &mut weighted_utxos).unwrap();
+
+        let expected_utxos = vec![WeightedUtxo {
+            satisfaction_weight: SATISFACTION_SIZE,
+            utxo: TxOut {
+                value: Amount::from_str("1 cBTC").unwrap(),
+                script_pubkey: ScriptBuf::new(),
+            },
+        }];
+
+        assert_eq!(utxo_match, expected_utxos);
     }
 
     #[test]
-    fn find_solution_one_cbtc() {
-        let _target = Amount::from_str("1.5 cBTC").unwrap();
-        let _weighted_utxos: Vec<WeightedUtxo> = create_weighted_utxos();
+    fn one_solution_two_coins() {
+        let target = Amount::from_str("4 cBTC").unwrap();
+
+        let mut weighted_utxos = vec![
+            WeightedUtxo {
+                satisfaction_weight: SATISFACTION_SIZE,
+                utxo: TxOut {
+                    value: Amount::from_str("4 cBTC").unwrap(),
+                    script_pubkey: ScriptBuf::new(),
+                },
+            },
+            WeightedUtxo {
+                satisfaction_weight: SATISFACTION_SIZE,
+                utxo: TxOut {
+                    value: Amount::from_str("3 cBTC").unwrap(),
+                    script_pubkey: ScriptBuf::new(),
+                },
+            },
+        ];
+
+        let utxo_match = select_coins_bnb(target, FEE_RATE, &mut weighted_utxos).unwrap();
+
+        let expected_utxos = vec![WeightedUtxo {
+            satisfaction_weight: SATISFACTION_SIZE,
+            utxo: TxOut {
+                value: Amount::from_str("4 cBTC").unwrap(),
+                script_pubkey: ScriptBuf::new(),
+            },
+        }];
 
-        //let utxo_match = select_coins_bnb(target, FEE_RATE, &mut weighted_utxos);
-        //let expected_bool_vec = vec![false, false, false, true];
-        //assert_eq!(expected_bool_vec, utxo_match);
+        assert_eq!(utxo_match, expected_utxos);
     }
 
     //#[test]
@@ -299,8 +413,8 @@ mod tests {
     //}
 
     #[test]
-    fn select_coins_bnb_no_solution() {
-        let target: Amount = Amount::from_str("4 cBTC").unwrap();
+    fn select_coins_bnb_not_enough_value() {
+        let target: Amount = Amount::from_str("11 cBTC").unwrap();
         let mut weighted_utxos: Vec<WeightedUtxo> = create_weighted_utxos();
 
         let result = select_coins_bnb(target, FEE_RATE, &mut weighted_utxos);