From 669821a64398dbe779282da1644863be7244180b Mon Sep 17 00:00:00 2001
From: tanshu <git@tanshu.com>
Date: Sat, 20 Mar 2021 08:05:50 +0530
Subject: [PATCH] Using Half-Round-Even rounding in the bill amounts as this is
 what python round uses. When the bill amounts were Odd number + .5, payment
 could not be received as javascript rounded it up, but python rounded it
 down. We are now using the python rounding (Half Round Even / Banker's
 Rounding) in the bill service.

---
 bookie/src/app/sales/bill.service.ts  | 17 ++++++++++-------
 bookie/src/app/shared/math.service.ts | 12 +++++++++++-
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/bookie/src/app/sales/bill.service.ts b/bookie/src/app/sales/bill.service.ts
index 3af4bce..fa5a51b 100644
--- a/bookie/src/app/sales/bill.service.ts
+++ b/bookie/src/app/sales/bill.service.ts
@@ -1,7 +1,6 @@
 import { SelectionModel } from '@angular/cdk/collections';
 import { Injectable } from '@angular/core';
 import { MatDialog } from '@angular/material/dialog';
-import { round } from 'mathjs';
 import { BehaviorSubject, throwError } from 'rxjs';
 import { Observable } from 'rxjs/internal/Observable';
 import { tap } from 'rxjs/operators';
@@ -14,9 +13,9 @@ import { SaleCategory } from '../core/sale-category';
 import { Table } from '../core/table';
 import { ToasterService } from '../core/toaster.service';
 import { ModifierCategoryService } from '../modifier-categories/modifier-category.service';
+import { MathService } from '../shared/math.service';
 
 import { Bill } from './bills/bill';
-import { BillSelectionItem } from './bills/bill-selection-item';
 import { Inventory } from './bills/inventory';
 import { Kot } from './bills/kot';
 import { VoucherType } from './bills/voucher-type';
@@ -39,6 +38,7 @@ export class BillService {
   constructor(
     private dialog: MatDialog,
     private toaster: ToasterService,
+    private math: MathService,
     private ser: VoucherService,
     private modifierCategoryService: ModifierCategoryService,
   ) {
@@ -75,7 +75,10 @@ export class BillService {
               productId: i.product.id,
               isHappyHour: i.isHappyHour,
               isPrinted: !!k.id,
-              info: `${i.product.name} @ ${i.price} - ${round(i.discount * 100, 2)}%`,
+              info: `${i.product.name} @ ${i.price} - ${this.math.halfRoundEven(
+                i.discount * 100,
+                2,
+              )}%`,
               quantity: i.quantity,
               modifiers: i.modifiers,
             }),
@@ -284,7 +287,7 @@ export class BillService {
 
   updateAmounts() {
     this.netAmount.next(
-      round(
+      this.math.halfRoundEven(
         this.bill.kots.reduce(
           (t, k) =>
             k.inventories.reduce((a, c) => a + (c.isHappyHour ? 0 : c.price) * c.quantity, 0) + t,
@@ -293,7 +296,7 @@ export class BillService {
       ),
     );
     this.discountAmount.next(
-      round(
+      this.math.halfRoundEven(
         this.bill.kots.reduce(
           (t, k) =>
             k.inventories.reduce(
@@ -305,7 +308,7 @@ export class BillService {
       ),
     );
     this.taxAmount.next(
-      round(
+      this.math.halfRoundEven(
         this.bill.kots.reduce(
           (t, k) =>
             k.inventories.reduce(
@@ -318,7 +321,7 @@ export class BillService {
       ),
     );
     this.amountBs.next(
-      round(
+      this.math.halfRoundEven(
         this.bill.kots.reduce(
           (t, k) =>
             k.inventories.reduce(
diff --git a/bookie/src/app/shared/math.service.ts b/bookie/src/app/shared/math.service.ts
index 83117e7..df37ee2 100644
--- a/bookie/src/app/shared/math.service.ts
+++ b/bookie/src/app/shared/math.service.ts
@@ -5,7 +5,6 @@ import { evaluate, round } from 'mathjs';
   providedIn: 'root',
 })
 export class MathService {
-  // eslint-disable-next-line class-methods-use-this
   parseAmount(amount: string = '', rounding: number = 2): number {
     const cleaned = `${amount}`.replace(new RegExp('(₹[s]*)|(,)|(s)', 'g'), '');
     if (cleaned === '') {
@@ -13,4 +12,15 @@ export class MathService {
     }
     return round(evaluate(cleaned), rounding);
   }
+
+  halfRoundEven(x: number, n = 0): number {
+    const fraction = Math.round(x * Math.pow(10, n + 8)) % Math.pow(10, 8);
+    if (fraction > 50000000 - 1 && fraction < 50000000 + 1) {
+      // To compensate for floating point rounding errors
+      const floor = Math.floor(x * Math.pow(10, n));
+      return floor % 2 === 0 ? floor / Math.pow(10, n) : (floor + 1) / Math.pow(10, n);
+    } else {
+      return round(x, n);
+    }
+  }
 }