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### Exchange
Everyone’s tasks are different and with the help of this functionality
you can add exchange rates to your wallets.
The wallet currency is set via meta. Example:
```php
$user->createWallet([
'name' => 'My USD Wallet',
'meta' => ['currency' => 'USD'],
]);
```
Service for working with currencies you need to write yourself or
use [library](https://github.com/bavix/laravel-wallet-swap).
#### Service for working with currency
We will write a simple service.
We will take the data from the array, and not from the database.
```php
use Bavix\Wallet\Internal\Service\MathServiceInterface;
use Bavix\Wallet\Services\ExchangeServiceInterface;
class MyExchangeService implements ExchangeServiceInterface
{
private array $rates = [
'USD' => [
'RUB' => 67.61,
],
];
private MathServiceInterface $mathService;
public function __construct(MathServiceInterface $mathService)
{
$this->mathService = $mathService;
foreach ($this->rates as $from => $rates) {
foreach ($rates as $to => $rate) {
if (empty($this->rates[$to][$from])) {
$this->rates[$to][$from] = $this->mathService->div(1, $rate);
}
}
}
}
/** @param float|int|string $amount */
public function convertTo(string $fromCurrency, string $toCurrency, $amount): string
{
return $this->mathService->mul($amount, $this->rates[$fromCurrency][$toCurrency] ?? 1);
}
}
```
#### Service Registration
The service you wrote must be registered, this is done in the file `config/wallet.php`.
```php
return [
// ...
'services' => [
'exchange' => MyExchangeService::class,
// ...
],
// ...
];
```
#### Exchange process
Create two wallets.
```php
$usd = $user->createWallet([
'name' => 'My Dollars',
'meta' => ['currency' => 'USD'],
]);
$rub = $user->createWallet([
'name' => 'My Ruble',
'meta' => ['currency' => 'RUB'],
]);
```
We replenish the ruble wallet with 100 rubles.
```php
$rub->deposit(10000);
```
We will exchange rubles into dollars.
```php
$transfer = $rub->exchange($usd, 10000);
$rub->balance; // 0
$usd->balance; // 147, это $1.47
```
Unfortunately, the world is not perfect. You will not get back your 100 rubles.
```php
$transfer = $usd->exchange($rub, $usd->balance);
$usd->balance; 0
$rub->balance; 9938
```
Due to conversion and mathematical rounding, you lost 62 kopecks.
You have 99 rubles 38 kopecks left.
---
It worked!