Greenfield: Add store rates api (#4550)

* Add store rates api

* Improve doc

---------

Co-authored-by: nicolas.dorier <nicolas.dorier@gmail.com>

BTCPayServer/Controllers/GreenField/GreenfieldStoreRatesController.cs

@@ -0,0 +1,84 @@
+#nullable enable
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using BTCPayServer.Abstractions.Constants;
+using BTCPayServer.Client;
+using BTCPayServer.Client.Models;
+using BTCPayServer.Data;
+using BTCPayServer.Rating;
+using BTCPayServer.Services.Rates;
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.Mvc;
+
+namespace BTCPayServer.Controllers.GreenField
+{
+    [ApiController]
+    [Route("api/v1/stores/{storeId}/rates")]
+    [Authorize(AuthenticationSchemes = AuthenticationSchemes.Greenfield)]
+    public class GreenfieldStoreRatesController : ControllerBase
+    {
+        private readonly RateFetcher _rateProviderFactory;
+        private readonly BTCPayNetworkProvider _btcPayNetworkProvider;
+
+        public GreenfieldStoreRatesController(
+            RateFetcher rateProviderFactory,
+            BTCPayNetworkProvider btcPayNetworkProvider)
+        {
+            _rateProviderFactory = rateProviderFactory;
+            _btcPayNetworkProvider = btcPayNetworkProvider;
+        }
+      
+        [HttpGet("")]
+        [Authorize(Policy = Policies.CanViewStoreSettings, AuthenticationSchemes = AuthenticationSchemes.Greenfield)]
+        public async Task<IActionResult> GetStoreRates([FromQuery] string[]? currencyPair)
+        {
+            var data = HttpContext.GetStoreData();
+            var blob = data.GetStoreBlob();
+            var parsedCurrencyPairs = new HashSet<CurrencyPair>();
+
+            if (currencyPair?.Any() is true)
+            {
+                foreach (var pair in currencyPair)
+                {
+                    if (!CurrencyPair.TryParse(pair, out var currencyPairParsed))
+                    {
+                        ModelState.AddModelError(nameof(currencyPair),
+                            $"Invalid currency pair '{pair}' (it should be formatted like BTC_USD,BTC_CAD)");
+                        break;
+                    }
+
+                    parsedCurrencyPairs.Add(currencyPairParsed);
+                }
+            }
+            else
+            {
+                parsedCurrencyPairs = blob.DefaultCurrencyPairs.ToHashSet();
+            }
+            
+
+            var rules = blob.GetRateRules(_btcPayNetworkProvider);
+
+
+            var rateTasks = _rateProviderFactory.FetchRates(parsedCurrencyPairs, rules, CancellationToken.None);
+            await Task.WhenAll(rateTasks.Values);
+            var result = new List<StoreRateResult>();
+            foreach (var rateTask in rateTasks)
+            {
+                var rateTaskResult = rateTask.Value.Result;
+
+                result.Add(new StoreRateResult()
+                {
+                    CurrencyPair = rateTask.Key.ToString(),
+                    Errors = rateTaskResult.Errors.Select(errors => errors.ToString()).ToList(),
+                    Rate = rateTaskResult.Errors.Any() ? null : rateTaskResult.BidAsk.Bid
+                });
+            }
+
+            return Ok(result);
+        }
+
+    }
+}