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Issue fix for Bug andrewagain#16 - Support for operator precedence
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@brindhavenkatesan
brindhavenkatesan committed Jul 23, 2020
1 parent 37b5607 commit 1d6cf81
Showing 1 changed file with 128 additions and 120 deletions.
248 changes: 128 additions & 120 deletions src/logic/calculate.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2,133 +2,141 @@ import Big from "big.js";

import operate from "./operate";
import isNumber from "./isNumber";

/**
* Given a button name and a calculator data object, return an updated
* calculator data object.
*
* Calculator data object contains:
* total:String the running total
* next:String the next number to be operated on with the total
* operation:String +, -, etc.
*/
export default function calculate(obj, buttonName) {
if (buttonName === "AC") {
return {
total: null,
next: null,
operation: null,
};
}

if (isNumber(buttonName)) {
if (buttonName === "0" && obj.next === "0") {
return {};
}
// If there is an operation, update next
if (obj.operation) {
if (obj.next) {
return { next: obj.next + buttonName };
}
return { next: buttonName };
}
// If there is no operation, update next and clear the value
if (obj.next) {
const next = obj.next === "0" ? buttonName : obj.next + buttonName;
return {
next,
total: null,
};
}
return {
next: buttonName,
total: null,
};
}
Calculator data object contains:
numStack - Numbers that are yet to be processed are pushed to stack.
operStack - Operators that are yet to be processed are pushed to stack.
lastNumPressed - Last number pressed by the user.
lastOperPressed - Last operaator pressed by the user.
lastPressed : "number" | "operator" - Whether last pressed
displayValue: The value displayed in the display area.
*/
export default function calculate(obj, key) {
let numStack = obj.numStack || [];
let operStack = obj.operStack || [];
let lastNumPressed = obj.lastNumPressed;
let lastOperPressed = obj.lastOperPressed;
let lastPressed = obj.lastPressed;
let displayValue = obj.displayValue;

if (buttonName === "%") {
if (obj.operation && obj.next) {
const result = operate(obj.total, obj.next, obj.operation);
return {
total: Big(result)
.div(Big("100"))
.toString(),
next: null,
operation: null,
};
}
if (obj.next) {
return {
next: Big(obj.next)
.div(Big("100"))
.toString(),
};
}
return {};
let processSingleOperation = ()=>{
let secondNum = numStack.pop();
let firstNum = numStack.pop();
let result = operate(firstNum, secondNum, operStack.pop());
numStack.push(parseFloat(result));
displayValue = result;
}

if (buttonName === ".") {
if (obj.next) {
// ignore a . if the next number already has one
if (obj.next.includes(".")) {
return {};

let processStack = (processAll)=>{
if(numStack.length>1){
if(lastPressed === "operator"){
operStack.pop();
}
if(processAll){
while(numStack.length>1){
processSingleOperation();
}
}else{
processSingleOperation();
}
return { next: obj.next + "." };
}
return { next: "0." };
}

if (buttonName === "=") {
if (obj.next && obj.operation) {
return {
total: operate(obj.total, obj.next, obj.operation),
next: null,
operation: null,
};
} else {
// '=' with no operation, nothing to do
return {};
}
return displayValue;
}

if (buttonName === "+/-") {
if (obj.next) {
return { next: (-1 * parseFloat(obj.next)).toString() };
}
if (obj.total) {
return { total: (-1 * parseFloat(obj.total)).toString() };
let validCalcKeys = ["AC", "+/-", "%", "÷", "7", "8", "9", "x", "4", "5", "6", "-", "1", "2", "3", "+","0", ".", "=", "Backspace"];
if(validCalcKeys.includes(key)){
if(key === "AC"){
numStack = [];
operStack = [];
lastNumPressed = null;
lastOperPressed = null;
lastPressed = null;
displayValue = null;
lastPressed = key;
}else if(key === "="){
processStack(true);
lastPressed = key;
}else if(key === "+/-"){
lastNumPressed = parseFloat(displayValue) * -1;
displayValue = String(lastNumPressed);
numStack.pop();
numStack.push(lastNumPressed);
lastPressed = key;
}else if(key === "Backspace"){
/** Last character is removed when backspace is pressed */
displayValue = displayValue.slice(0, displayValue.length-1);
lastNumPressed = parseFloat(displayValue || 0);
numStack.pop();
numStack.push(lastNumPressed);
lastPressed = "number";
}else{
let isDecimalPt = key === ".";
if(isNumber(key) && (!isDecimalPt || !displayValue.includes("."))){
if(lastPressed === "number"){
displayValue = (displayValue === "0" && !isDecimalPt ? "" : displayValue) + key;
/* Since we are concating to the previous number, we need to replace the last pushed value */
numStack.pop();
}else{
/* On pressing (= (or) +/- (or) AC), the previous numbers are omitted.
*/
if(lastPressed === "=" || lastPressed === "+/-"){
numStack=[];
}
displayValue = isDecimalPt ? "0." : key;
}
lastNumPressed = parseFloat(displayValue || 0);
numStack.push(lastNumPressed)
lastPressed = "number";
}else{
if(key === '%'){
if(displayValue && displayValue !== "0"){
if(lastPressed === 'operator'){
operStack.pop();
}
let updatedNum = Big(displayValue).div(Big("100"));
numStack.pop();
numStack.push(updatedNum);
displayValue = String(updatedNum);
lastPressed = "number";
}
}else{
if(lastPressed){
if(lastPressed === "operator"){
/**
* If lastpressed key is an operator, it has to be replaced.
*/
operStack.pop();
}else{
/**
* Behavior implemented from Mac calculator.
* 1. If last pressed operator precedence is equalto / morethan the current operators hierachy, the previous operations are calculated before proceeding with the current one.
* 2. (x|÷|%) has high precedence than (+|-)
*/
let getPrecedence = (operator)=> ["x", "÷"].includes(operator);
let currentOperPrecedence = getPrecedence(key);
let prevOperPrecedence = getPrecedence(lastOperPressed);
if ((currentOperPrecedence === prevOperPrecedence) || (currentOperPrecedence<prevOperPrecedence)){
processStack();
lastNumPressed = parseFloat(displayValue);
}
}
}
if(!numStack.length){
numStack.push(0);
}
operStack.push(key);
lastPressed = "operator";
}
lastOperPressed = key;
}
}
return {};
}

// Button must be an operation

// When the user presses an operation button without having entered
// a number first, do nothing.
// if (!obj.next && !obj.total) {
// return {};
// }

// User pressed an operation button and there is an existing operation
if (obj.operation) {
return {
total: operate(obj.total, obj.next, obj.operation),
next: null,
operation: buttonName,
};
}

// no operation yet, but the user typed one

// The user hasn't typed a number yet, just save the operation
if (!obj.next) {
return { operation: buttonName };
return{
numStack,
operStack,
lastOperPressed,
lastNumPressed,
lastPressed,
displayValue: displayValue || "0"
}

// save the operation and shift 'next' into 'total'
return {
total: obj.next,
next: null,
operation: buttonName,
};
}
}

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