using System.Text.Json;

var builder = WebApplication.CreateBuilder(args);

// Add services to the container.
// Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
builder.Services.AddOpenApi();

var app = builder.Build();

// Configure the HTTP request pipeline.
if (app.Environment.IsDevelopment())
{
    app.MapOpenApi();
    app.UseSwaggerUI(options => options.SwaggerEndpoint("/openapi/v1.json", "Open API V1"));
}

List<string> gCurrencies = ["USD", "EUR", "GBP"];
var gHttpClient = new HttpClient();
var gJsonSerializerOptions = new JsonSerializerOptions(JsonSerializerDefaults.Web);
var gSemaphoreSlim = new SemaphoreSlim(1, 1);

// Add route and a function that serves the result.
app.MapGet("/rates/average", () => GetAverageRateAsync(gCurrencies)).WithOpenApi();

app.MapPost("/rates", async (string currency) =>
{
    gSemaphoreSlim.Wait();
        gCurrencies.Add(currency);
    gSemaphoreSlim.Release();
}).WithOpenApi();

app.MapDelete("/rates/{currency}", async (string currency) =>
{
    lock (gSemaphoreSlim)
        gCurrencies.Remove(currency);
}).WithOpenApi();

app.Run();

decimal ParsePrice(string json)
{
    var result = JsonSerializer.Deserialize<CurrencyExchangeRatesResult>(json, gJsonSerializerOptions);
    return result!.Data.Rates["CZK"];
}

async Task<decimal> GetAverageRateAsync(List<string> currencies)
{
    decimal sum = 0;
    gSemaphoreSlim.Wait();
    {
        foreach (var currency in currencies)
        {
            var json = await gHttpClient.GetStringAsync($"https://api.coinbase.com/v2/exchange-rates?currency={currency}");
            sum += ParsePrice(json);
        }
    }
    gSemaphoreSlim.Release();

    var avg = sum / currencies.Count;

    return avg;
}

public record CurrencyExchangeRatesResult(CurrencyExchangeRates Data);
public record CurrencyExchangeRates(string Currency, IReadOnlyDictionary<string, decimal> Rates);