Currency Conversion

Mix.install([
  {:jason, "~> 1.4"},
  {:kino, "~> 0.9", override: true},
  {:youtube, github: "brooklinjazz/youtube"},
  {:hidden_cell, github: "brooklinjazz/hidden_cell"}
])

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Currency Conversion

You are building an app which accepts payments. Originally, your app was built assuming it would only accept a single currency, however it expands to accept multiple currencies.

You are tasked with the assignment of converting one currency to another according to the following conversion rates.

• Canadian Dollar (:CAD): $1.00
• US Dollar (:USD): $1.29
• European Euro (:EUR): $1.39

While not a perfect solution, you may round currency conversions using round/1.

For example, 500 :EUR would become 360 :CAD.

round(500 / 1.39)

Remember that currency should not be stored in a float, instead money will be stored in a Money struct where :amount is stored as an integer of cents.

> “If I had a dime for every time I’ve seen someone use FLOAT to store currency, I’d have $999.997634” – Bill Karwin

• Create a Money struct with :amount and :currency.
• Create a convert/2 function to convert a money struct from one currency to another.
• Create an add/2 function to add one money struct of the same currency to another.
• Create a subtract/2 function to subtract one money struct of the same currency to another.
• Create a multiply function to multiply one money struct by a number.

Examples

five_eur = Money.new(500, :EUR)
%Money{amount: 500, currency: :EUR}

Money.convert(five_eur, :CAD)
%Money{amount: 695, currency: :EUR}

ten_eur = Money.add(five_eur, five_eur)
%Money{amount: 10_00, currency: :EUR}

hundred_eur = Money.multiply(ten_eur, 10)
%Money{amount: 100_00, currency: :EUR}

ninety_nine_eur = Money.subtract(hundred_eur, ten_eur)
%Money{amount: 90, currency: :EUR}

Money.add(%Money{amount: 500, :EUR}, %Money{amount: 500, :CAD})
** (FunctionClauseError) no function clause matching in Money.add/2

Enter your solution below.

defmodule Money do
  defstruct []

  @doc ~S"""
  Create a new `Money` struct with the given `amount` and `currency`.

  ## Examples

      iex> Money.new(500, :CAD)
      %Money{amount: 500, currency: :CAD}

  """
  def new(amount, currency) do
  end

  @doc ~S"""
  Converts a `Money` struct from its current currency to the given `currency`.

  ## Examples

      iex> Money.new(500, :CAD) |> Money.convert(:EUR)
      %Money{amount: 360, currency: :EUR}

  """
  def convert(money, currency) do
  end

  @doc ~S"""
  Adds two `Money` structs of the same currency to one another.

  ## Examples

      iex> Money.new(500, :CAD) |> Money.add(Money.new(500, :CAD))
      %Money{amount: 1000, currency: :CAD}

  """
  def add(money1, money2) do
  end

  @doc ~S"""
  Multiplies a `Money` struct by the given `multiplier`.

  ## Examples

      iex> Money.new(100, :CAD) |> Money.multiply(10)
      %Money{amount: 1000, currency: :CAD}

      iex> Money.new(100, :CAD) |> Money.multiply(1.1)
      %Money{amount: 110, currency: :CAD}

  """
  def multiply(money, multiplier) do
  end

  @doc ~S"""
  Subtracts `money2` from `money1` given they are `Money` structs with the same currency.

  ## Examples

      iex> Money.new(10_000, :USD) |> Money.subtract(Money.new(100, :USD)
      %Money{amount: 9900, currency: :USD}

  """
  def subtract(money1, money2) do
  end
end

This exercise is inspired by the Elixir Money library.

Mark As Completed

file_name = Path.basename(Regex.replace(~r/#.+/, __ENV__.file, ""), ".livemd")

progress_path = __DIR__ <> "/../progress.json"
existing_progress = File.read!(progress_path) |> Jason.decode!()

default = Map.get(existing_progress, file_name, false)

form =
  Kino.Control.form(
    [
      completed: input = Kino.Input.checkbox("Mark As Completed", default: default)
    ],
    report_changes: true
  )

Task.async(fn ->
  for %{data: %{completed: completed}} <- Kino.Control.stream(form) do
    File.write!(progress_path, Jason.encode!(Map.put(existing_progress, file_name, completed)))
  end
end)

form

Commit Your Progress

Run the following in your command line from the curriculum folder to track and save your progress in a Git commit. Ensure that you do not already have undesired or unrelated changes by running git status or by checking the source control tab in Visual Studio Code.

$ git checkout solutions
$ git checkout -b currency-conversion-exercise
$ git add .
$ git commit -m "finish currency conversion exercise"
$ git push origin currency-conversion-exercise

Create a pull request from your currency-conversion-exercise branch to your solutions branch. Please do not create a pull request to the DockYard Academy repository as this will spam our PR tracker.

DockYard Academy Students Only:

Notify your instructor by including @BrooklinJazz in your PR description to get feedback. You (or your instructor) may merge your PR into your solutions branch after review.

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