//! 传输层的错误类型。
//! Error type for the transport layer.

use std::fmt;

/// 传输层可能产生的错误。
/// Errors that can arise in the transport layer.
#[derive(Debug)]
pub enum TransportError {
    /// URL 格式非法或不被支持。
    /// The URL was malformed or unsupported.
    BadUrl(String),
    /// DNS 解析失败。
    /// DNS resolution failed.
    Dns(String),
    /// 网络 I/O 错误（TCP、TLS 或 HTTP）。
    /// A network I/O error (TCP, TLS, or HTTP).
    Io(String),
    /// TLS 握手失败。
    /// The TLS handshake failed.
    Tls(String),
    /// 服务器返回非 2xx 状态码或格式错误的响应。
    /// The server returned a non-2xx status or a malformed response.
    Http { status: u16, body: String },
    /// 请求超时。
    /// A timeout elapsed.
    Timeout,
}

impl fmt::Display for TransportError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            TransportError::BadUrl(m) => write!(f, "bad url: {}", m),
            TransportError::Dns(m) => write!(f, "dns error: {}", m),
            TransportError::Io(m) => write!(f, "io error: {}", m),
            TransportError::Tls(m) => write!(f, "tls error: {}", m),
            TransportError::Http { status, body } => {
                write!(f, "http error {}: {}", status, body)
            }
            TransportError::Timeout => write!(f, "request timed out"),
        }
    }
}

impl std::error::Error for TransportError {}

/// 将 std::io::Error 转换为传输层错误（归入 Io 变体）。
/// Convert a std::io::Error into a transport error (as the Io variant).
impl From<std::io::Error> for TransportError {
    fn from(e: std::io::Error) -> Self {
        TransportError::Io(e.to_string())
    }
}

/// 传输层操作的统一返回类型别名。
/// Standard Result alias for transport operations.
pub type TransportResult<T> = Result<T, TransportError>;