From c4818c4bc8a34e44ce856c92d217b6c981606c95 Mon Sep 17 00:00:00 2001
From: Christopher Jeffrey <chjjeffrey@gmail.com>
Date: Fri, 12 Feb 2016 02:44:11 -0800
Subject: [PATCH] add subtract fee option.

---
 lib/bcoin/tx.js | 78 +++++++++++++++++++++++++++++--------------------
 1 file changed, 46 insertions(+), 32 deletions(-)

diff --git a/lib/bcoin/tx.js b/lib/bcoin/tx.js
index f415d56a..08a666dc 100644
--- a/lib/bcoin/tx.js
+++ b/lib/bcoin/tx.js
@@ -1014,22 +1014,31 @@ TX.prototype.maxSize = function maxSize() {
 };
 
 TX.prototype.getInputs = function getInputs(unspent, address, fee) {
+  var self = this;
   var tx = this.clone();
-  var cost = tx.getOutputValue();
+  var outputValue = tx.getOutputValue();
   var totalkb = 1;
-  var total = cost.addn(constants.tx.minFee);
   var inputs = [];
   var lastAdded = 0;
-  var size, newkb, change;
-
-  if (fee)
-    total = cost.add(fee);
+  var minFee = constants.tx.minFee;
+  var dustThreshold = constants.tx.dustThreshold;
+  var i, size, newkb, change;
 
   // Oldest unspents first
   unspent = unspent.slice().sort(function(a, b) {
     return a.height - b.height;
   });
 
+  function total() {
+    if (self.subtractFee)
+      return outputValue;
+    return outputValue.add(fee);
+  }
+
+  function isFull() {
+    return tx.getInputValue().cmp(total()) >= 0;
+  }
+
   function addCoins() {
     var i, index;
 
@@ -1042,15 +1051,20 @@ TX.prototype.getInputs = function getInputs(unspent, address, fee) {
       lastAdded++;
 
       // Stop once we're full.
-      if (tx.getInputValue().cmp(total) >= 0)
+      if (isFull())
         break;
     }
   }
 
-  // Transfer `total` funds maximum.
-  addCoins();
+  if (fee) {
+    // Transfer `total` funds maximum.
+    addCoins();
+  } else {
+    fee = new bn(minFee);
+
+    // Transfer `total` funds maximum.
+    addCoins();
 
-  if (!fee) {
     // Add dummy output (for `change`) to
     // calculate maximum TX size.
     tx.addOutput({
@@ -1058,17 +1072,6 @@ TX.prototype.getInputs = function getInputs(unspent, address, fee) {
       value: new bn(0)
     });
 
-    // if (this.subtractFee) {
-    //   var f = new bn((Math.ceil(tx.maxSize() / 1024) - 1) * constants.tx.minFee);
-    //   for (var j = 0; j < this.outputs.length; j++) {
-    //     if (this.outputs[j].value.cmp(f.addn(constants.tx.dustThreshold)) >= 0) {
-    //       this.outputs[j].value = this.outputs[j].value.sub(f);
-    //       break;
-    //     }
-    //   }
-    //   total = tx.getInputValue();
-    // }
-
     // Change fee value if it is more than 1024
     // bytes (10000 satoshi for every 1024 bytes).
     do {
@@ -1076,30 +1079,42 @@ TX.prototype.getInputs = function getInputs(unspent, address, fee) {
       size = tx.maxSize();
 
       newkb = Math.ceil(size / 1024) - totalkb;
-      total.iaddn(newkb * constants.tx.minFee);
+      fee.iaddn(newkb * minFee);
       totalkb += newkb;
 
       // Failed to get enough funds, add more inputs.
-      if (tx.getInputValue().cmp(total) < 0)
+      if (!isFull())
         addCoins();
-    } while (tx.getInputValue().cmp(total) < 0 && lastAdded < unspent.length);
+    } while (!isFull() && lastAdded < unspent.length);
   }
 
-  if (tx.getInputValue().cmp(total) < 0) {
+  if (!isFull()) {
     // Still failing to get enough funds.
     inputs = null;
   } else {
     // How much money is left after filling outputs.
-    change = tx.getInputValue().sub(total);
+    change = tx.getInputValue().sub(total());
+
+    // Attempt to subtract fee.
+    if (this.subtractFee) {
+      for (i = 0; i < tx.outputs.length; i++) {
+        if (tx.outputs[i].value.cmp(fee.addn(dustThreshold)) >= 0) {
+          tx.outputs[i].value.isub(fee);
+          break;
+        }
+      }
+      // Could not subtract fee
+      if (i === tx.outputs.length)
+        inputs = null;
+    }
   }
 
   // Return necessary inputs and change.
   return {
     inputs: inputs,
     change: change,
-    cost: cost,
-    fee: total.sub(cost),
-    total: total,
+    fee: fee,
+    total: total(),
     kb: totalkb,
     unspent: unspent.slice(0, lastAdded)
   };
@@ -1144,6 +1159,8 @@ TX.prototype.fill = function fill(unspent, address, fee) {
     });
 
     this.changeIndex = this.outputs.length - 1;
+
+    assert.equal(this.getFee().toNumber(), result.fee.toNumber());
   }
 
   return result;
@@ -1209,9 +1226,6 @@ TX.prototype._recalculateFee = function recalculateFee() {
   real = Math.ceil(size / 1024) * constants.tx.minFee;
   fee = this.getFee().toNumber();
 
-  // if (this.hardFee)
-  //   real = this.hardFee;
-
   if (real === fee) {
     if (this.changeIndex === -1)
       this.outputs.pop();