Calculator Example

Here are a few different versions of the Calculator application.

Basic Single Page Calculator

from bakery import assert_equal
from dataclasses import dataclass
from drafter import *


@dataclass
class State:
    """
    The application state has two numbers, which are actually stored as
    strings. Users can type anything they want into the boxes, and we want
    to remember the values they write, even if they are not valid numbers.
    We must remember to convert them before using them.

    The result stores the actual result to be shown to the user. Could also
    be an error message if something goes wrong.
    """
    first_number: str
    second_number: str
    result: str


@route
def index(state: State) -> Page:
    """
    In this version, the textboxes are on the front page, a there's
    a button to go to the page that actually adds the values together.
    Then, the bottom shows the latest result.
    """
    return Page(state, [
        "What is the first number?",
        TextBox("first", state.first_number),
        "What is the second number?",
        TextBox("second", state.second_number),
        Button("Add", add_page),
        "The result is",
        state.result
    ])


@route
def add_page(state: State, first: str, second: str) -> Page:
    """
    This is the page with the actual logic. The first and second textboxes
    values are sent here and stored in the state.
    If they are both composed of digits, then their sum is calculated.
    Otherwise, an error is stored in the result.
    Finally, we reuse the logic for showing the index page.
    """
    state.first_number = first
    state.second_number = second

    if first.isdigit() and second.isdigit():
        state.result = str(int(first) + int(second))
    else:
        state.result = "Invalid numbers!"

    return index(state)


# Test that the front page loads normally
assert_equal(index(State("0", "0", "")),
             Page(State("0", "0", ''),
                  ['What is the first number?',
                   TextBox('first', "0"),
                   'What is the second number?',
                   TextBox('second', "0"),
                   Button('Add', add_page),
                   'The result is',
                   '']))

# Test that the add page works with zeroes
assert_equal(add_page(State("0", "0", ""), "0", "0"),
             Page(State("0", "0", '0'),
                  ['What is the first number?',
                   TextBox('first', "0"),
                   'What is the second number?',
                   TextBox('second', '0'),
                   Button('Add', add_page),
                   'The result is',
                   '0']))

# Test that the add page can take more interesting numbers
# Keyword parameters can be used to make the values more explicit.
# Copying the body generated from the page may introduce them!
assert_equal(add_page(State("0", "0", ""), "5", "3"),
             Page(state=State(first_number="5", second_number="3", result='8'),
                  content=['What is the first number?',
                           TextBox(name='first', default_value="5"),
                           'What is the second number?',
                           TextBox(name='second', default_value="3"),
                           Button(text='Add', url=add_page),
                           'The result is',
                           '8']))

# Test that the add page can take more interesting numbers
# Keyword parameters can be used to make the values more explicit.
# Copying the body generated from the page may introduce them!
assert_equal(add_page(State("0", "0", ""), "five", "three"),
             Page(state=State(first_number="five", second_number="three",
                              result='Invalid numbers!'),
                  content=['What is the first number?',
                           TextBox(name='first', default_value="five"),
                           'What is the second number?',
                           TextBox(name='second', default_value="three"),
                           Button(text='Add', url=add_page),
                           'The result is',
                           'Invalid numbers!']))

# Default state for this application is two zeroes and no result.
start_server(State("0", "0", ""))