import 'package:flutter/material.dart';

void main() => runApp(const CalculatorApp());

class CalculatorApp extends StatelessWidget {
   const CalculatorApp({super.key});

   @override
   Widget build(BuildContext context) {
      return MaterialApp(
         title: 'Calculator',
         home: const CalculatorScreen(),
      );
   }
}

class CalculatorScreen extends StatefulWidget {
   const CalculatorScreen({super.key});

   @override
   State<CalculatorScreen> createState() => CalculatorScreenState();
}

class CalculatorScreenState extends State<CalculatorScreen> {
   String input = "0";
   String operand = "";
   String operator = "";
   String history = "";
  
 
   void buttonPressed(String text) {
      setState(() {
         if (text == "C") {
            input = "0";
            operand = "";
            operator = "";
            history = "";
      } else if (text == "=") {
         evaluateExpression();
      } else {
         history = history + text;
         if (text == "+" || text == "-" || text == "*" || text == "/") {
            operator = text;
            operand = input;
            input = "0";
         } else {
            input =  input == "0" ? text : input + text;
         }
      }
      });
   }

   void evaluateExpression() {
      double num1 = double.tryParse(operand) ?? 0;
      double num2 = double.tryParse(input) ?? 0;
      double result;

      switch (operator) {
         case "+": result = num1 + num2;
            break;
         case "-": result = num1 - num2;
            break;
         case "*": result = num1 * num2;
            break;
         case "/": result = num1 / num2;
            break;
         default: result = 0;
            break;
      }
      if (result == result.toInt()) { history = "$history = ${result.toInt()}\n"; }
      else { history = "$history = $result\n"; }
      input = "0";
      operand = "";
      operator = "";
   }
   
   Widget buildButton(String text, {Color? color}) {
      return Expanded(
         child: Container(
            padding: const EdgeInsets.all(8),
            child: TextButton(
               style: TextButton.styleFrom(
                  backgroundColor: color ?? Colors.grey[900],
                  foregroundColor: Colors.white,
                  padding: const EdgeInsets.symmetric(vertical: 20),
               ),
               onPressed: () => buttonPressed(text),
               child: Center( 
                  child: Text(text,
                     style: const TextStyle(fontSize: 40),
                  ),
               ),
            ),
         ),
      );
   }

   Widget buildButtonRow(List<Map<String, dynamic>> buttons) {
      return Row(
         children: buttons.map((btn) => buildButton(btn['label'], color: btn['color'],)).toList(),
      );
   }

   @override
   Widget build(BuildContext context) {
      return Scaffold(
         backgroundColor: Colors.black,
         body: Column(
            mainAxisAlignment: MainAxisAlignment.end,
            crossAxisAlignment: CrossAxisAlignment.start,
            children: [
               Text(history, style: const TextStyle(fontSize: 40, color: Colors.white)),
               Text(input, style: const TextStyle(fontSize: 56, color: Colors.white)),
               buildButtonRow([
                  {'label': '7'},
                  {'label': '8'},
                  {'label': '9'},
                  {'label': '/', 'color': Colors.orange},
               ]),
               buildButtonRow([
                  {'label': '4'},
                  {'label': '5'},
                  {'label': '6'},
                  {'label': '*', 'color': Colors.orange},
               ]),
               buildButtonRow([
                  {'label': '1'},
                  {'label': '2'},
                  {'label': '3'},
                  {'label': '-', 'color': Colors.orange},
               ]),
               buildButtonRow([
                  {'label': '0'},
                  {'label': 'C', 'color': Colors.red},
                  {'label': '=', 'color': Colors.green},
                  {'label': '+', 'color': Colors.orange},
               ]),
               const SizedBox(height: 30),
            ],
         ),
      );
  }
}