// Program.cs — IHttpClientFactory 등록
builder.Services.AddHttpClient("weather", client =>
{
    client.BaseAddress = new Uri("https://api.weather.example.com/");
    client.DefaultRequestHeaders.Add("Accept", "application/json");
    client.Timeout = TimeSpan.FromSeconds(10);
});

// 서비스에서 사용
public class WeatherService(IHttpClientFactory httpFactory)
{
    public async Task<WeatherData?> GetAsync(string city, CancellationToken ct)
    {
        var client = httpFactory.CreateClient("weather");
        return await client.GetFromJsonAsync<WeatherData>($"current/{city}", ct);
    }
}

// ❌ 매 요청마다 new + Dispose — socket exhaustion 유발
public async Task<string> GetDataAsync(string url)
{
    using var client = new HttpClient(); // 소켓 낭비
    return await client.GetStringAsync(url);
}

// ❌ static 재사용으로 socket exhaustion은 해결했지만 DNS 갱신 문제 발생
private static readonly HttpClient _client = new();

public async Task<string> GetDataAsync(string url)
{
    // DNS가 바뀌어도 _client는 이전 연결을 계속 사용
    return await _client.GetStringAsync(url);
}

// Program.cs / DI 등록

// 1. 기명 클라이언트 — 이름으로 구분하여 설정
builder.Services.AddHttpClient("github", client =>
{
    client.BaseAddress = new Uri("https://api.github.com/");
    client.DefaultRequestHeaders.UserAgent.ParseAdd("MyApp/1.0");
});

// 2. 타입 지정 클라이언트 — 서비스 타입으로 바인딩 (권장)
builder.Services.AddHttpClient<GitHubService>(client =>
{
    client.BaseAddress = new Uri("https://api.github.com/");
    client.DefaultRequestHeaders.UserAgent.ParseAdd("MyApp/1.0");
});

// 타입 지정 클라이언트 구현
public class GitHubService(HttpClient client)
{
    public async Task<Repo[]?> GetReposAsync(string user, CancellationToken ct)
        => await client.GetFromJsonAsync<Repo[]>($"users/{user}/repos", ct);
}

// GET — JSON 응답을 직접 역직렬화
var user = await client.GetFromJsonAsync<UserDto>($"users/{id}", ct);

// POST — 객체를 JSON으로 직렬화하여 전송
var newUser = new CreateUserRequest { Name = "Mina", Email = "mina@example.com" };
var response = await client.PostAsJsonAsync("users", newUser, ct);
response.EnsureSuccessStatusCode();
var created = await response.Content.ReadFromJsonAsync<UserDto>(ct);

// PUT
await client.PutAsJsonAsync($"users/{id}", updateRequest, ct);

// DELETE
var delResponse = await client.DeleteAsync($"users/{id}", ct);
delResponse.EnsureSuccessStatusCode();

// 응답 상태 코드 확인이 필요할 때 — GetAsync 사용
using var res = await client.GetAsync($"users/{id}", ct);
if (res.StatusCode == HttpStatusCode.NotFound) return null;
res.EnsureSuccessStatusCode();
var dto = await res.Content.ReadFromJsonAsync<UserDto>(ct);

public async Task<WeatherData?> GetWeatherAsync(string city, CancellationToken externalCt)
{
    // 요청별 timeout: 5초
    using var timeoutCts = new CancellationTokenSource(TimeSpan.FromSeconds(5));

    // 외부 취소 신호(예: ASP.NET Core 요청 취소) + 요청 timeout 결합
    using var linkedCts  = CancellationTokenSource.CreateLinkedTokenSource(
        externalCt, timeoutCts.Token);

    try
    {
        return await _client.GetFromJsonAsync<WeatherData>(
            $"current/{city}", linkedCts.Token);
    }
    catch (OperationCanceledException) when (timeoutCts.IsCancellationRequested)
    {
        _logger.LogWarning("날씨 API 요청 시간 초과: {City}", city);
        return null;
    }
}