# CurrencyConversion

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Convert Money Amounts between currencies. This library uses an OTP worker to save current conversion rates.

## Installation

The package can be installed by adding `currency_conversion` to your list of dependencies in `mix.exs`:

def deps do
    {:currency_conversion, "~> 0.3"},
    {:jason, "~> 1.1"}, # When usig Fixer / Exchange Rates API,
    {:httpotion, "~> 3.1"}, # When usig Fixer / Exchange Rates API

## Setup

`CurrencyConversion` is a wrapper around the currency conversion. We can define an
implementation as follows:

defmodule MyApp.CurrencyConversion do
  use CurrencyConversion, otp_app: :my_app

If your application was generated with a supervisor (by passing `--sup` to `mix new`)
you will have a `lib/my_app/application.ex` file containing the application start
callback that defines and starts your supervisor. You just need to edit the `start/2`
function to start the converter as a supervisor on your application's supervisor:

def start(_type, _args) do
  children = [
    {MyApp.CurrencyConversion, []}
  opts = [strategy: :one_for_one, name: MyApp.Supervisor]
  Supervisor.start_link(children, opts)

## Configuration

- `source` - Configure which Data Source Should Be Used.
  * Type: `atom`
  * Default: `CurrencyConversion.Source.ExchangeRatesApi`
  * Restrictions: Must implement `CurrencyConversion.Source` behaviour
  * Given Implementations:
    - `CurrencyConversion.Source.Fixer` - [Fixer](
    - `CurrencyConversion.Source.ExchangeRatesApi` - [Exchange Rates API](
    - `CurrencyConversion.Source.Test` - Test Source
- `base_currency` - Change the base currency that is requested when fetching rates
  * Type: `atom`
  * Default: `:EUR`
- `refresh_interval` - Configure how often the data should be refreshed (in ms) or turn auto-refresh off.
  * Type: `integer | :manual`
  * Default: `86_400_000` (Once per Day)
  * `:manual` turns auto-refresh off, do refresh yourself
- `seed` - Deliver the rates data manually.
  * Type: `(Keyword.t() -> {:ok, CurrencyConversion.Rates.t()} | {:error, binary}) | {module :: atom, function :: atom, arity :: 1}`
  * Default: Load from `source`
- `test_rates` - Configure rates for `CurrencyConversion.Source.Test` source
  * Type: `{atom, %{atom: float}}`
  * Default: see `CurrencyConversion.Source.Test.@default_rates`
  * Example: `{:EUR, %{CHF: 7.0}}`

config :my_app, MyApp.CurrencyConversion,
  source: CurrencyConversion.Source.Fixer,
  source_api_key: "FIXER_ACCESS_KEY",
  # defaults to http since free access key only supports http
  source_protocol: "https",
  refresh_interval: 86_400_000

## Custom Source

A custom source can be implemented by using the behaviour `CurrencyConversion.Source` and reconfiguring the `source` config.

It only has to implement the function `load/0`, which produces a struct of type `%CurrencyConversion.Rates{}`.

## Test

To prevent HTTP calls in the Tests, configure the Test Source. (See the configuration `test_rates` for custom test rates.)

config :my_app, MyApp.CurrencyConversion,
  source: CurrencyConversion.Source.Test,
  refresh_interval: 86_400_000

## Usage

Only the callbacks from `CurrencyConversion` are exposed to the user. The library
[money]( is used to represent money amounts.

### Example

Change 7 swiss franks to dollars:

iex> MyApp.CurrencyConversion.convert(, :CHF), :USD)
%Money{amount: 10_50, currency: :USD}

Get supported currencies:

iex> MyApp.CurrencyConversion.get_currencies()
[:EUR, :USD, :CHF, ...]

Manually refresh exchange rates:

iex> MyApp.CurrencyConversion.refresh_rates()