From 09aa8ebfc46c10981b0b8baf6dcf618f40d1e167 Mon Sep 17 00:00:00 2001
From: yancy <yancy@yancy.lol>
Date: Tue, 5 Nov 2024 12:22:34 -0600
Subject: [PATCH] Add sort_by

---
 src/coin_grinder.rs | 52 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 src/coin_grinder.rs

diff --git a/src/coin_grinder.rs b/src/coin_grinder.rs
new file mode 100644
index 0000000..bc856c2
--- /dev/null
+++ b/src/coin_grinder.rs
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: CC0-1.0
+//
+//! Coin Grinder.
+//!
+//! This module introduces the Coin Grinder selection Algorithm
+//!
+/// Coin Grinder is a DFS-based selection Algorithm which optimises for transaction weight.
+///
+/// # Parameters
+///
+/// * target: Target spend `Amount`
+/// * change_target: A bound on the `Amount` to increase target by with which to create a change
+/// output.
+/// * max_selection_weight: Maximum allowable selection weight. 
+/// * weighted_utxos: The candidate Weighted UTXOs from which to choose a selection from
+
+use crate::WeightedUtxo;
+use bitcoin::Amount;
+use bitcoin::FeeRate;
+use bitcoin::SignedAmount;
+
+pub fn coin_grinder<Utxo: WeightedUtxo>(
+    target: Amount,
+    cost_of_change: Amount,
+    fee_rate: FeeRate,
+    long_term_fee_rate: FeeRate,
+    weighted_utxos: &[Utxo],
+) -> Option<std::vec::IntoIter<&Utxo>> {
+
+    // Creates a tuple of (effective_value, weighted_utxo)
+    let mut w_utxos: Vec<(Amount, &Utxo)> = weighted_utxos
+        .iter()
+        // calculate effective_value and waste for each w_utxo.
+        .map(|wu| (wu.effective_value(fee_rate), wu))
+        // remove utxos that either had an error in the effective_value or waste calculation.
+        .filter(|(eff_val, _)| eff_val.is_some())
+        // unwrap the option type since we know they are not None (see previous step).
+        .map(|(eff_val, wu)| (eff_val.unwrap(), wu))
+        // filter out all effective_values that are negative.
+        .filter(|(eff_val, _)| eff_val.is_positive())
+        // all utxo effective_values are now positive (see previous step) - cast to unsigned.
+        .map(|(eff_val, wu)| (eff_val.to_unsigned().unwrap(), wu))
+        .collect();
+
+    // decending sort by effective_value using weight as tie breaker.
+    w_utxos.sort_by(|a, b| { 
+        b.0.cmp(&a.0)
+            .then(b.1.satisfaction_weight().cmp(&a.1.satisfaction_weight()))
+    });
+
+    None
+}