Calculator

lib/widgets/components/calculator/calculator-button.dart

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+import 'package:flutter/material.dart';
+
+typedef void CalculatorButtonTapCallback({String buttonText});
+
+class CalculatorButton extends StatelessWidget {
+  CalculatorButton({this.text, @required this.onTap});
+
+  final String text;
+  final CalculatorButtonTapCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    return Expanded(
+        child: Container(
+            decoration: BoxDecoration(
+              border: Border.all(
+                color: Color.fromRGBO(0, 0, 0, 0.1),
+                width: 0.5,
+              ),
+            ),
+            child: FlatButton(
+              onPressed: () => onTap(buttonText: text),
+              child: Text(
+                text,
+                style: TextStyle(fontSize: 18, fontWeight: FontWeight.w500),
+              ),
+              padding: EdgeInsets.all(30),
+              highlightColor: Colors.blueGrey[100],
+              splashColor: Colors.blueAccent[100],
+            )));
+  }
+}

lib/widgets/components/calculator/calculator-buttons.dart

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+import 'package:flutter/material.dart';
+import 'calculator.dart';
+import 'calculator-button.dart';
+import 'calculator-row.dart';
+
+class CalculatorButtons extends StatelessWidget {
+  CalculatorButtons({@required this.onTap});
+
+  final CalculatorButtonTapCallback onTap;
+  final calculatorButtonRows = [
+    ['7', '8', '9', Calculations.DIVIDE],
+    ['4', '5', '6', Calculations.MULTIPLY],
+    ['1', '2', '3', Calculations.SUBTRACT],
+    [Calculations.PERIOD, '0', '00', Calculations.ADD],
+    [Calculations.CLEAR, Calculations.EQUAL]
+  ];
+
+  @override
+  Widget build(BuildContext context) {
+    return Column(
+      children: calculatorButtonRows.map((calculatorRowButtons) {
+        return CalculatorRow(
+          buttons: calculatorRowButtons,
+          onTap: onTap,
+        );
+      }).toList()
+    );
+  }
+}

lib/widgets/components/calculator/calculator-row.dart

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+import 'package:flutter/material.dart';
+import 'calculator-button.dart';
+
+class CalculatorRow extends StatelessWidget {
+  CalculatorRow({@required this.buttons, @required this.onTap });
+
+  final List<String> buttons;
+  final CalculatorButtonTapCallback onTap;
+
+  @override
+  Widget build(BuildContext context) {
+    return Row(
+      children: rowButtons(),
+      mainAxisAlignment: MainAxisAlignment.spaceAround,
+    );
+  }
+
+  List<Widget> rowButtons() {
+    List<Widget> rowButtons = [];
+
+    buttons.forEach((String buttonText) {
+      rowButtons.add(
+        CalculatorButton(
+          text: buttonText,
+          onTap: onTap,
+        ),
+      );
+    });
+
+    return rowButtons;
+  }
+}

lib/widgets/components/calculator/calculator.dart

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+import 'number-formatter.dart';
+
+class Calculations {
+  static const PERIOD = '.';
+  static const MULTIPLY = '*';
+  static const SUBTRACT = '-';
+  static const ADD = '+';
+  static const DIVIDE = '/';
+  static const CLEAR = 'CLEAR';
+  static const EQUAL = '=';
+  static const OPERATIONS = [
+    Calculations.ADD,
+    Calculations.MULTIPLY,
+    Calculations.SUBTRACT,
+    Calculations.DIVIDE,
+  ];
+
+  static double add(double a, double b) => a + b;
+  static double subtract(double a, double b) => a - b;
+  static double divide(double a, double b) => a / b;
+  static double multiply(double a, double b) => a  * b;
+}
+
+class Calculator {
+  static String parseString(String text) {
+    List<String> numbersToAdd;
+    double a, b, result;
+    if (text.contains(Calculations.ADD)) {
+      numbersToAdd = text.split(Calculations.ADD);
+      a = double.parse(numbersToAdd[0]);
+      b = double.parse(numbersToAdd[1]);
+
+      result = Calculations.add(a, b);
+    } else if (text.contains(Calculations.MULTIPLY)) {
+      numbersToAdd = text.split(Calculations.MULTIPLY);
+      a = double.parse(numbersToAdd[0]);
+      b = double.parse(numbersToAdd[1]);
+
+      result = Calculations.multiply(a, b);
+    } else if (text.contains(Calculations.DIVIDE)) {
+      numbersToAdd = text.split(Calculations.DIVIDE);
+      a = double.parse(numbersToAdd[0]);
+      b = double.parse(numbersToAdd[1]);
+
+      result = Calculations.divide(a, b);
+    } else if (text.contains(Calculations.SUBTRACT)) {
+      numbersToAdd = text.split(Calculations.SUBTRACT);
+      a = double.parse(numbersToAdd[0]);
+      b = double.parse(numbersToAdd[1]);
+
+      result = Calculations.subtract(a, b);
+    } else {
+      return text;
+    }
+
+    return NumberFormatter.format(result.toString());
+  }
+
+  static String addPeriod(String calculatorString) {
+    if (calculatorString.isEmpty) {
+      return calculatorString = '0${Calculations.PERIOD}';
+    }
+
+    RegExp exp = new RegExp(r"\d\.");
+    Iterable<Match> matches = exp.allMatches(calculatorString);
+    int maxMatches = Calculator.includesOperation(calculatorString) ? 2 : 1;
+
+    return matches.length == maxMatches
+        ? calculatorString
+        : calculatorString += Calculations.PERIOD;
+  }
+
+  static bool includesOperation(String calculatorString) {
+    for (var operation in Calculations.OPERATIONS) {
+      if (calculatorString.contains(operation)) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+}

lib/widgets/components/calculator/number-display.dart

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+import 'package:flutter/material.dart';
+
+class NumberDisplay extends StatelessWidget {
+  NumberDisplay({this.value: ''});
+
+  final String value;
+
+  @override
+  Widget build(BuildContext context) {
+    return Padding(
+        padding: EdgeInsets.all(20),
+        child: Row(
+          children: <Widget>[
+            Text(
+              value,
+              style: TextStyle(fontSize: 40, fontWeight: FontWeight.bold),
+            ),
+          ],
+          mainAxisAlignment: MainAxisAlignment.end,
+        ));
+  }
+}

lib/widgets/components/calculator/number-formatter.dart

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+class NumberFormatter {
+  static String format(String text) {
+    try {
+      double parsedNumber = double.parse(text);
+
+      if ((parsedNumber != double.infinity) && (parsedNumber == parsedNumber.floor())) {
+        return parsedNumber.truncate().toString();
+      }
+
+      return text;
+    } catch(err) {
+      return text;
+    }
+  }
+}