wallet: add SelectionResult::GetChange

1 files changed, 21 insertions, 0 deletions

diff --git a/src/wallet/coinselection.h b/src/wallet/coinselection.h
index d1038a117a..dd52241e2a 100644
--- a/src/wallet/coinselection.h
+++ b/src/wallet/coinselection.h
@@ -303,6 +303,8 @@ public:
     /** Get the sum of the input values */
     [[nodiscard]] CAmount GetSelectedValue() const;
 
+    [[nodiscard]] CAmount GetSelectedEffectiveValue() const;
+
     void Clear();
 
     void AddInput(const OutputGroup& group);
@@ -320,6 +322,25 @@ public:
 
     bool operator<(SelectionResult other) const;
 
+    /** Get the amount for the change output after paying needed fees.
+     *
+     * The change amount is not 100% precise due to discrepancies in fee calculation.
+     * The final change amount (if any) should be corrected after calculating the final tx fees.
+     * When there is a discrepancy, most of the time the final change would be slightly bigger than estimated.
+     *
+     * Following are the possible factors of discrepancy:
+     *  + non-input fees always include segwit flags
+     *  + input fee estimation always include segwit stack size
+     *  + input fees are rounded individually and not collectively, which leads to small rounding errors
+     *  - input counter size is always assumed to be 1vbyte
+     *
+     * @param[in]  min_viable_change  Minimum amount for change output, if change would be less then we forgo change
+     * @param[in]  change_fee         Fees to include change output in the tx
+     * @returns Amount for change output, 0 when there is no change.
+     *
+     */
+    CAmount GetChange(const CAmount min_viable_change, const CAmount change_fee) const;
+
     CAmount GetTarget() const { return m_target; }
 
     SelectionAlgorithm GetAlgo() const { return m_algo; }