From 9ab73d965b3a0d7859bb6e33490d4cb2d94c8f28 Mon Sep 17 00:00:00 2001
From: ignacio 'nacho' velazco <ignaciovelazco12@gmail.com>
Date: Fri, 19 Jun 2020 15:49:55 -0300
Subject: [PATCH] fix: support the sum of negative numbers (#11)

BREAKING CHANGE: sum negative numbers

* fix: support the sum of negative numbers

* test: add test for mixed amounts
---
 src/sum-prop.js      | 25 +++----------------------
 src/sum-prop.test.js | 27 ++++++++++++++-------------
 2 files changed, 17 insertions(+), 35 deletions(-)

diff --git a/src/sum-prop.js b/src/sum-prop.js
index 2988bce..7317974 100644
--- a/src/sum-prop.js
+++ b/src/sum-prop.js
@@ -1,23 +1,10 @@
 'use strict';
 
-const {
-  compose,
-  applyTo,
-  propOr,
-  reduce,
-  pair,
-  useWith,
-  identity,
-  sum,
-  when,
-  lt,
-  always,
-  gt
-} = require('ramda');
+const { compose, applyTo, propOr, reduce, pair, useWith, identity, sum } = require('ramda');
 const curryN = require('./curry-n');
 const castArray = require('./cast-array');
 const { rejectNilOrEmpty } = require('./reject-nil');
-const { MAX_MATH_DELTA, MIN_MATH_DELTA } = require('./utils/_math-constants');
+const round = require('./round');
 
 /**
  * Sums the values at `propName` present in each element of an array.
@@ -37,13 +24,7 @@ function sumProp(precision, propName, values) {
   return applyTo(
     values,
     compose(
-      // Round to two decimal places
-      total =>
-        Number.isFinite(total) ? +(Math.round(total + `e+${precision}`) + `e-${precision}`) : total,
-      // Coerce values higher than `Number.MAX_SAFE_INTEGER` to `Infinity`
-      when(lt(MAX_MATH_DELTA), always(Infinity)),
-      // Coerce values lower than `0.0000001` to `0`
-      when(gt(MIN_MATH_DELTA), always(0)),
+      round(precision),
       reduce(useWith(compose(sum, pair), [identity, compose(Number, propOr(0, propName))]), 0),
       rejectNilOrEmpty,
       castArray
diff --git a/src/sum-prop.test.js b/src/sum-prop.test.js
index bf3663d..64697bd 100644
--- a/src/sum-prop.test.js
+++ b/src/sum-prop.test.js
@@ -32,19 +32,20 @@ test('should ignore `undefined` elements in the array', () => {
   expect(sumProp(2, 'amount', [{ amount: 30 }, undefined, { amount: 12 }, undefined])).toBe(42);
 });
 
-test('should underflow total value to zero if sum is lower than `1e-7`', () => {
-  expect(
-    sumProp(1, 'amount', [
-      { amount: 85 },
-      { amount: -294.21 },
-      { amount: 294.21 },
-      { amount: -219.5 },
-      { amount: -85 },
-      { amount: -219.5 }
-    ])
-  ).toBe(0);
-});
-
 test('should overflow result to `Infinity` if sum goes above `MAX_SAFE_INTEGER`', () => {
   expect(sumProp(1, 'amount', [{ amount: Number.MAX_SAFE_INTEGER }, { amount: 1 }])).toBe(Infinity);
 });
+
+test('should underflow total value to zero if sum is betweem `1e-7` and `-1e-7`', () => {
+  expect(sumProp(2, 'foo', [{ foo: 0.00000000001 }, { foo: 0.00000000002 }])).toBe(0);
+
+  expect(sumProp(2, 'foo', [{ foo: -0.00000000001 }, { foo: -0.00000000002 }])).toBe(0);
+});
+
+test('should sum all negative numeric values present at the given property in the array', () => {
+  expect(sumProp(2, 'amount', [{ amount: -10 }, { amount: -20 }, { amount: -12 }])).toBe(-42);
+});
+
+test('should sum all numeric values ( negatives and positives ) present at the given property in the array', () => {
+  expect(sumProp(2, 'amount', [{ amount: -10 }, { amount: 20 }, { amount: -12 }])).toBe(-2);
+});