nachocss/stringcalculatordart

The following is a TDD + BLoC Kata, an enchanced version of the classic kata for Flutter.

String Calculator Kata for Flutter

The following is a TDD + BLoC Kata.

This classic kata guides you step by step through the implementation of a calculator that receives a String as input. It is a good exercise on refactoring and incremental implementation. It is also a good candidate for practising TDD.

First step

Create a function add that takes a String and returns a String:

String add(String number)

• The method can take 0, 1 or 2 numbers separated by comma, and returns their sum.
• An empty string will return “0”.
• Example of inputs: "", "1", "1.1,2.2".

Many numbers

Allow the add method to handle an unknow number of arguments.

Newline as separator

Allow the add method to handle newlines as separators:

• "1\n2,3" should return "6".
• "175.2,\n35" is invalid and should return the message "Number expected but '\n' found at position 6."

Missing number in last position

Don’t allow the input to end in a separator.

• "1,3," is invalid and should return the message Number expected but EOF found.

Custom separators

Allow the add method to handle a different delimiter. To change the delimiter, the beginning of the input will contain a separate line that looks like this:

//[delimiter]\n[numbers]

• "//;\n1;2" should return "3"
• "//|\n1|2|3" should return "6"
• "//sep\n2sep3" should return "5"
• "//|\n1|2,3" is invalid and should return the message "'|' expected but ',' found at position 3."

All existing scenarios should work as before.

Negative numbers

Calling add with negative numbers will return the message "Negative not allowed : " listing all negative numbers that were in the list of numbers.

• "-1,2" is invalid and should return the message "Negative not allowed : -1"
• "2,-4,-5" is invalid and should return the message "Negative not allowed : -4, -5"

Multiple errors

Calling add with multiple errors will return all error messages separated by newlines.

• "-1,,2" is invalid and return the message "Negative not allowed : -1\nNumber expected but ',' found at position 3."

Errors management

Introduce an internal add function returning a number instead of a String, and test many solutions for the error messages. - Exception - maybe and monad approch - POSIX return code with message managemement - tuple with error struct like in Go - etc.

Other operations

Write a function for multiply with same rules

From this point, the goal is to practice the BLoC pattern

Get user input by GUI

Create a Widget that contains an input text field. This Widget will add an Event to the Stream when pressing ENTER.

Process the new Event

When our new event is created, call the function add and get the result and print it through console.

Print the result in the GUI

Create a new Widget that will print the result of the function add.

Inform through a text field if anything went wrong

Tell the user what happened in case an error was found.

Create a Dialog that informs about the error

First, build a basic Dialog that just contains text. Then, add an Accept button to be able to close it.

Allow navigation between States

Add a BACK button that takes you from the final State to the Initial State

Support navigation using the phone's back button

In order to do this, you should check WillPopScope widget and its parameter onWillPop.

Support other operations

In the input State, let the user to choose the operation to be calculated.

Display a notification if the input is empty

Let the user know that he needs to insert the factors to calculate with. A good way to achieve this is by implementing a SnackBar.