Converting BRL to BTC and BTC to BRL using the public orderbook from FOXBIT Exchange

foxbit-convert-values.php

<?php

/**
 * Converting BRL to BTC and BTC to BRL using the public orderbook from FOXBIT Exchange
 *
 * NOTE
 * - use CURL to get the orderbook
 * - use BCMath for arithmetic
 */

function getOrderbook()
{
    // Foxbit public orderbook
    $orderbookPublicUrl = 'https://api.blinktrade.com/api/v1/BRL/orderbook';

    $curl = curl_init();
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl, CURLOPT_URL, $orderbookPublicUrl);

    // JSON to array
    $orderbook = json_decode(curl_exec($curl), true);

    curl_close($curl);

    return $orderbook;
}

function convertBrlToBtc($brlValue)
{
    // BCMath precision
    bcscale(8);

    // Assert using string because of BCMath
    $brlValue = strval($brlValue);

    // Copy $brlValue to calculate average later
    $brlValueCopy = $brlValue;

    $btcAmount = "0";
    $orderbook = getOrderbook();
    $len = sizeof($orderbook['asks']);
    $i = 0;

    while (bccomp($brlValue, "0") === 1 && $i < $len) {
        $unitPrice = strval($orderbook['asks'][$i][0]);
        $amount    = strval($orderbook['asks'][$i][1]);

        $portion = bcmul($unitPrice, $amount);

        if (bccomp($brlValue, $portion) === -1) {
            $btcAmount = bcadd($btcAmount, bcdiv($brlValue, $unitPrice));
            $brlValue  = "0";
        } else {
            $brlValue  = bcsub($brlValue, $portion);
            $btcAmount = bcadd($btcAmount, $amount);
        }

        $i++;
    }

    return array(
        'amount'  => $btcAmount,
        'left'    => $brlValue,
        'average' => bcdiv(bcsub($brlValueCopy, $brlValue), $btcAmount)
    );
}

function convertBtcToBrl($btcValue)
{
    // BCMath precision
    bcscale(8);

    // Assert using string because of BCMath
    $btcValue = strval($btcValue);

    // Copy $btcValue to calculate average later
    $btcValueCopy = $btcValue;

    $brlAmount = "0";
    $orderbook = getOrderbook();
    $len = sizeof($orderbook['bids']);
    $i = 0;

    while (bccomp($btcValue, "0") === 1 && $i < $len) {
        $unitPrice = strval($orderbook['bids'][$i][0]);
        $amount    = strval($orderbook['bids'][$i][1]);

        $portion = bcmul($unitPrice, $amount);

        if (bccomp($btcValue, $amount) === -1) {
            $brlAmount = bcadd($brlAmount, bcmul($unitPrice, $btcValue));
            $btcValue  = "0";
        } else {
            $btcValue  = bcsub($btcValue, $amount);
            $brlAmount = bcadd($brlAmount, $portion);
        }

        $i++;
    }

    return array(
        'amount'  => $brlAmount,
        'left'    => $btcValue,
        'average' => bcdiv($brlAmount, bcsub($btcValueCopy, $btcValue))
    );
}

$brlValue = "1234.89";
echo "Converting R$ ".$brlValue." to BTC:\n";
print_r(convertBrlToBtc($brlValue));

echo "\n";

$btcValue = "0.87983321";
echo "Converting ".$btcValue." BTC to R$:\n";
print_r(convertBtcToBrl($btcValue));