refactor: extract rate formatting logic to RateService and add tests

app/Services/RateService.php

@@ -0,0 +1,51 @@
+<?php
+
+namespace App\Services;
+
+use App\Models\City;
+use App\Models\Rate;
+
+class RateService
+{
+    public function getFormattedRates(): array
+    {
+        $supportedCities = City::query()
+            ->whereIn('name', City::supportedCities()) // Filter only supported cities
+            ->get()
+            ->sortByDesc(fn($city) => $city->name === 'sanaa') // Sort to put 'sanaa' first
+            ->values();  // Reset array keys to be sequential
+
+        // Get the latest exchange rates for each currency in each city
+        $latestRates = Rate::query()
+            ->with('currency', 'city')
+            ->orderBy('city_id', 'asc')
+            ->orderBy('currency_id', 'asc')
+            ->orderBy('date', 'desc')
+            ->get()
+            ->groupBy(fn($rate) => $rate->city_id . '-' . $rate->currency_id)
+            ->map(fn($group) => $group->first())
+            ->groupBy('city_id');
+
+
+        // Format the rates
+        $rates = $supportedCities->map(function ($city) use ($latestRates) {
+            $cityRates = $latestRates->get($city->id, collect())->map(function ($rate) {
+                return [
+                    'currency'    => $rate->currency->name,
+                    'buy_price'   => $rate->buy_price,
+                    'sell_price'  => $rate->sell_price,
+                    'date'        => $rate->date->toDateString(),
+                    'day'         => $rate->date->locale('ar')->isoFormat('dddd'),
+                    'last_update' => $rate->updated_at->diffForHumans(),
+                ];
+            })->values()->toArray();
+
+            return [
+                'city'  => $city->label ,
+                'rates' => $cityRates,
+            ];
+        })->toArray();
+
+        return $rates;
+    }
+}