在 C# 與 .NET 使用匯率

// Program.cs
using System.Net.Http.Headers;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddHttpClient<FxClient>(client =>
{
    var key = builder.Configuration["EXCHANGERATE_API_KEY"]
        ?? throw new InvalidOperationException("EXCHANGERATE_API_KEY is missing");

    client.BaseAddress = new Uri("https://api.exchangerate.dev/v1/");
    client.DefaultRequestHeaders.Authorization =
        new AuthenticationHeaderValue("Bearer", key);
    client.Timeout = TimeSpan.FromSeconds(5);
});

// FxClient.cs
using System.Net.Http.Json;
using System.Text.Json.Serialization;

public sealed record LatestRates(
    string Base,
    string Source,
    [property: JsonPropertyName("market_session")] string MarketSession,
    [property: JsonPropertyName("data_updated_at")] DateTimeOffset DataUpdatedAt,
    Dictionary<string, decimal> Rates
);

public sealed class FxClient(HttpClient http)
{
    public async Task<LatestRates> GetLatestAsync(
        string baseCurrency,
        CancellationToken cancellationToken)
    {
        using var response = await http.GetAsync(
            $"latest/{baseCurrency}?symbols=EUR,GBP",
            cancellationToken);

        response.EnsureSuccessStatusCode();

        return await response.Content.ReadFromJsonAsync<LatestRates>(
            cancellationToken: cancellationToken)
            ?? throw new InvalidOperationException("Empty FX response");
    }
}

var app = builder.Build();

app.MapGet("/fx", async (
    FxClient fx,
    CancellationToken cancellationToken) =>
{
    var rates = await fx.GetLatestAsync("USD", cancellationToken);

    return Results.Ok(new {
        eur = rates.Rates["EUR"],
        rates.Source,
        rates.MarketSession,
        rates.DataUpdatedAt,
    });
});

app.Run();