This makes the expense chart on the frontpage multi-currency.

app/Generator/Chart/Basic/ChartJsGenerator.php

@@ -39,6 +39,8 @@ class ChartJsGenerator implements GeneratorInterface
      *    'type' => bar or line, optional
      *    'yAxisID' => ID of yAxis, optional, will not be included when unused.
      *    'fill' => if to fill a line? optional, will not be included when unused.
+     *    'currency_symbol' => 'x',
+     *    'backgroundColor' => 'x',
      *    'entries' =>
      *        [
      *         'label-of-entry' => 'value'

app/Http/Controllers/Chart/AccountController.php

@@ -65,7 +65,7 @@ class AccountController extends Controller
 
 
     /**
-     * Shows the balances for all the user's expense accounts.
+     * Shows the balances for all the user's expense accounts (on the front page).
      *
      * @param AccountRepositoryInterface $repository
      *
@@ -86,23 +86,50 @@ class AccountController extends Controller
         }
         $start->subDay();
 
+        /** @var CurrencyRepositoryInterface $currencyRepos */
+        $currencyRepos = app(CurrencyRepositoryInterface::class);
+        $currencies    = [];
+        $chartData     = [
+            [
+                'label'           => (string)trans('firefly.spent'),
+                'type'            => 'bar',
+                'currency_symbol' => '¤',
+                'backgroundColor' => 'rgba(219, 68, 55, 0.5)', // red
+                'entries'         => [],
+            ],
+        ];
         $accounts      = $repository->getAccountsByType([AccountType::EXPENSE, AccountType::BENEFICIARY]);
-        $startBalances = app('steam')->balancesByAccounts($accounts, $start);
-        $endBalances   = app('steam')->balancesByAccounts($accounts, $end);
-        $chartData     = [];
+        $accountNames  = $this->extractNames($accounts);
+        $startBalances = app('steam')->balancesPerCurrencyByAccounts($accounts, $start);
+        $endBalances   = app('steam')->balancesPerCurrencyByAccounts($accounts, $end);
+        $tempData      = [];
 
-        foreach ($accounts as $account) {
-            $id           = $account->id;
-            $startBalance = $startBalances[$id] ?? '0';
-            $endBalance   = $endBalances[$id] ?? '0';
-            $diff         = bcsub($endBalance, $startBalance);
-            if (0 !== bccomp($diff, '0')) {
-                $chartData[$account->name] = $diff;
+
+        foreach ($endBalances as $accountId => $expenses) {
+            $accountId = (int)$accountId;
+            foreach ($expenses as $currencyId => $endAmount) {
+                $currencyId              = (int)$currencyId;
+                $startAmount             = $startBalances[$accountId][$currencyId] ?? '0';
+                $diff                    = bcsub($endAmount, $startAmount);
+                $currencies[$currencyId] = $currencies[$currencyId] ?? $currencyRepos->findNull($currencyId);
+                $title                   = (string)trans(
+                    'firefly.account_in_currency', ['account' => $accountNames[$accountId], 'currency' => $currencies[$currencyId]->name]
+                );
+                $tempData[$title]        = $diff;
             }
         }
+        arsort($tempData, SORT_NUMERIC);
 
-        arsort($chartData);
-        $data = $this->generator->singleSet((string)trans('firefly.spent'), $chartData);
+        foreach ($tempData as $label => $entry) {
+            if (0 !== bccomp($entry, '0')) {
+                $chartData[0]['entries'][$label] = $entry;
+            }
+        }
+        if (1 === \count($currencies)) {
+            $first                           = array_first($currencies);
+            $chartData[0]['currency_symbol'] = $first->symbol;
+        }
+        $data = $this->generator->multiSet($chartData);
         $cache->store($data);
 
         return response()->json($data);
@@ -507,4 +534,51 @@ class AccountController extends Controller
         return $data;
     }
 
+    /**
+     * @param Collection $accounts
+     *
+     * @return array
+     */
+    private function extractNames(Collection $accounts): array
+    {
+        $return = [];
+        /** @var Account $account */
+        foreach ($accounts as $account) {
+            $return[$account->id] = $account->name;
+        }
+
+        return $return;
+    }
+
+    /**
+     * This method extracts the unique currency ID's from an array of balances.
+     *
+     * The given array is expected to be in this format:
+     *
+     * accountID1:
+     *  currencyID1: balance
+     *  currencyID2: balance
+     * accountID2:
+     *  currencyID1: balance
+     *  currencyID2: balance
+     *
+     *
+     * @param array $balances
+     *
+     * @return array
+     */
+    private function getCurrencyIDs(array $balances): array
+    {
+        $currencies = [];
+        /**
+         * @var int   $accountId
+         * @var array $info
+         */
+        foreach ($balances as $accountId => $info) {
+            $currencies = array_merge(array_keys($info));
+        }
+
+        return array_unique($currencies);
+    }
+
 }

app/Support/Steam.php

@@ -31,6 +31,7 @@ use FireflyIII\Repositories\Account\AccountRepositoryInterface;
 use Illuminate\Contracts\Encryption\DecryptException;
 use Illuminate\Support\Collection;
 use Log;
+use stdClass;
 
 /**
  * Class Steam.
@@ -211,6 +212,38 @@ class Steam
         return $balances;
     }
 
+    /**
+     * @param \FireflyIII\Models\Account $account
+     * @param \Carbon\Carbon             $date
+     *
+     * @return string
+     */
+    public function balancePerCurrency(Account $account, Carbon $date): array
+    {
+
+        // abuse chart properties:
+        $cache = new CacheProperties;
+        $cache->addProperty($account->id);
+        $cache->addProperty('balance-per-currency');
+        $cache->addProperty($date);
+        if ($cache->has()) {
+            return $cache->get(); // @codeCoverageIgnore
+        }
+        $query    = $account->transactions()
+                            ->leftJoin('transaction_journals', 'transaction_journals.id', '=', 'transactions.transaction_journal_id')
+                            ->where('transaction_journals.date', '<=', $date->format('Y-m-d 23:59:59'))
+                            ->groupBy('transactions.transaction_currency_id');
+        $balances = $query->get(['transactions.transaction_currency_id', DB::raw('SUM(transactions.amount) as sum_for_currency')]);
+        $return   = [];
+        /** @var stdClass $entry */
+        foreach ($balances as $entry) {
+            $return[(int)$entry->transaction_currency_id] = $entry->sum_for_currency;
+        }
+        $cache->store($return);
+
+        return $return;
+    }
+
     /**
      * This method always ignores the virtual balance.
      *
@@ -243,6 +276,38 @@ class Steam
         return $result;
     }
 
+    /**
+     * Same as above, but also groups per currency.
+     *
+     * @param \Illuminate\Support\Collection $accounts
+     * @param \Carbon\Carbon                 $date
+     *
+     * @return array
+     */
+    public function balancesPerCurrencyByAccounts(Collection $accounts, Carbon $date): array
+    {
+        $ids = $accounts->pluck('id')->toArray();
+        // cache this property.
+        $cache = new CacheProperties;
+        $cache->addProperty($ids);
+        $cache->addProperty('balances-per-currency');
+        $cache->addProperty($date);
+        if ($cache->has()) {
+            return $cache->get(); // @codeCoverageIgnore
+        }
+
+        // need to do this per account.
+        $result = [];
+        /** @var Account $account */
+        foreach ($accounts as $account) {
+            $result[$account->id] = $this->balancePerCurrency($account, $date);
+        }
+
+        $cache->store($result);
+
+        return $result;
+    }
+
     /**
      * @param int $isEncrypted
      * @param     $value

resources/lang/en_US/firefly.php

@@ -183,6 +183,7 @@ return [
     'scopes_will_be_able'                        => 'This application will be able to:',
     'button_authorize'                           => 'Authorize',
     'none_in_select_list'                        => '(none)',
+    'account_in_currency'                        => ':account in :currency',
 
     // check for updates:
     'update_check_title'                         => 'Check for updates',