typespec 0.14.0

// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT License.

//! Interfaces for working with errors.

#[cfg(feature = "http")]
use crate::http::{RawResponse, StatusCode};
use std::borrow::Cow;
use std::fmt::{Debug, Display};

/// A convenience alias for `Result` where the error type is hard coded to [`Error`].
pub type Result<T> = std::result::Result<T, Error>;

/// The kind of error.
///
/// The classification of error is intentionally fairly coarse.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum ErrorKind {
    /// An HTTP status code that was not expected.
    #[cfg(feature = "http")]
    HttpResponse {
        /// An HTTP status code.
        status: StatusCode,
        /// An error code returned by the service, or a friendly description of the `status`.
        error_code: Option<String>,
        /// The raw response returned by the service.
        raw_response: Option<Box<RawResponse>>,
    },
    /// A connection to the server could not be established.
    ///
    /// The request was never sent, so it is safe to retry both reads and writes.
    Connection,
    /// An error performing IO.
    Io,
    /// An error converting data.
    DataConversion,
    /// An error getting an API credential token.
    Credential,
    /// A catch all for other kinds of errors.
    Other,
}

impl ErrorKind {
    /// Consumes the `ErrorKind` and converts to an [`Error`].
    pub fn into_error(self) -> Error {
        Error {
            context: Repr::Simple(self),
        }
    }
}

impl Display for ErrorKind {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            #[cfg(feature = "http")]
            ErrorKind::HttpResponse {
                status, error_code, ..
            } => f
                .debug_tuple("HttpResponse")
                .field(status)
                .field(&error_code.as_deref().unwrap_or("(unknown error code)"))
                .finish(),
            ErrorKind::Connection => f.write_str("Connection"),
            ErrorKind::Io => f.write_str("Io"),
            ErrorKind::DataConversion => f.write_str("DataConversion"),
            ErrorKind::Credential => f.write_str("Credential"),
            ErrorKind::Other => f.write_str("Other"),
        }
    }
}

/// An error encountered when communicating with the service.
#[derive(Debug)]
pub struct Error {
    context: Repr,
}

impl Error {
    /// Create a new `Error` based on an [`ErrorKind`] and an underlying error cause.
    pub fn new<E>(kind: ErrorKind, error: E) -> Self
    where
        E: Into<Box<dyn std::error::Error + Send + Sync>>,
    {
        Self {
            context: Repr::Custom(Custom {
                kind,
                error: error.into(),
            }),
        }
    }

    /// Create a new `Error` based on an [`ErrorKind`], an underlying error cause, and a message.
    #[must_use]
    pub fn with_error<E, C>(kind: ErrorKind, error: E, message: C) -> Self
    where
        E: Into<Box<dyn std::error::Error + Send + Sync>>,
        C: Into<Cow<'static, str>>,
    {
        Self {
            context: Repr::CustomMessage(
                Custom {
                    kind,
                    error: error.into(),
                },
                message.into(),
            ),
        }
    }

    /// Create a new `Error` based on an [`ErrorKind`], an underlying error cause, and a function that returns a message.
    #[must_use]
    pub fn with_error_fn<E, F, C>(kind: ErrorKind, error: E, f: F) -> Self
    where
        E: Into<Box<dyn std::error::Error + Send + Sync>>,
        F: FnOnce() -> C,
        C: Into<Cow<'static, str>>,
    {
        Self::with_error(kind, error, f())
    }

    /// Create an `Error` based on an [`ErrorKind`] and a message.
    #[must_use]
    pub fn with_message<C>(kind: ErrorKind, message: C) -> Self
    where
        C: Into<Cow<'static, str>>,
    {
        Self {
            context: Repr::SimpleMessage(kind, message.into()),
        }
    }

    /// Creates an `Error` based on an [`ErrorKind`] and a function that returns a message.
    #[must_use]
    pub fn with_message_fn<F, C>(kind: ErrorKind, f: F) -> Self
    where
        F: FnOnce() -> C,
        C: Into<Cow<'static, str>>,
    {
        Self::with_message(kind, f())
    }

    /// Wrap this error with an additional message.
    #[must_use]
    pub fn with_context<C>(self, message: C) -> Self
    where
        C: Into<Cow<'static, str>>,
    {
        Self::with_error(self.kind().clone(), self, message)
    }

    /// Wrap this error with an additional message returned from a function.
    #[must_use]
    pub fn with_context_fn<F, C>(self, f: F) -> Self
    where
        F: FnOnce() -> C,
        C: Into<Cow<'static, str>>,
    {
        self.with_context(f())
    }

    /// Get the [`ErrorKind`] of this `Error`.
    pub fn kind(&self) -> &ErrorKind {
        match &self.context {
            Repr::Simple(kind)
            | Repr::SimpleMessage(kind, ..)
            | Repr::Custom(Custom { kind, .. })
            | Repr::CustomMessage(Custom { kind, .. }, _) => kind,
        }
    }

    /// If this error is an HTTP response error, return the associated status code.
    #[cfg(feature = "http")]
    pub fn http_status(&self) -> Option<StatusCode> {
        match &self.kind() {
            ErrorKind::HttpResponse { status, .. } => Some(*status),
            _ => None,
        }
    }

    /// Consumes the `Error`, returning its inner error, if any.
    pub fn into_inner(self) -> std::result::Result<Box<dyn std::error::Error + Send + Sync>, Self> {
        match self.context {
            Repr::Custom(Custom { error, .. }) | Repr::CustomMessage(Custom { error, .. }, _) => {
                Ok(error)
            }
            _ => Err(self),
        }
    }

    /// Consumes the error, attempting to downcast the inner error as the type provided.
    ///
    /// Returns `Err(self)` if the downcast is not possible.
    pub fn into_downcast<T: std::error::Error + 'static>(self) -> std::result::Result<T, Self> {
        if self.downcast_ref::<T>().is_none() {
            return Err(self);
        }
        // Unwrapping is ok here since we already check above that the downcast will work
        Ok(*self.into_inner()?.downcast().expect("downcast is Some(T)"))
    }

    /// Returns a reference to the inner error wrapped by this error, if any.
    pub fn get_ref(&self) -> Option<&(dyn std::error::Error + Send + Sync + 'static)> {
        match &self.context {
            Repr::Custom(Custom { error, .. }) | Repr::CustomMessage(Custom { error, .. }, _) => {
                Some(error.as_ref())
            }
            _ => None,
        }
    }

    /// Returns a reference to the inner error, if any, downcast to the type provided.
    pub fn downcast_ref<T: std::error::Error + 'static>(&self) -> Option<&T> {
        self.get_ref()?.downcast_ref()
    }

    /// Returns a mutable reference to the inner error wrapped by this error, if any.
    pub fn get_mut(&mut self) -> Option<&mut (dyn std::error::Error + Send + Sync + 'static)> {
        match &mut self.context {
            Repr::Custom(Custom { error, .. }) | Repr::CustomMessage(Custom { error, .. }, _) => {
                Some(error.as_mut())
            }
            _ => None,
        }
    }

    /// Returns a mutable reference to the inner error, if any, downcasting to the type provided.
    pub fn downcast_mut<T: std::error::Error + 'static>(&mut self) -> Option<&mut T> {
        self.get_mut()?.downcast_mut()
    }
}

impl std::error::Error for Error {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match &self.context {
            Repr::Custom(Custom { error, .. }) | Repr::CustomMessage(Custom { error, .. }, _) => {
                Some(&**error)
            }
            _ => None,
        }
    }
}

impl From<ErrorKind> for Error {
    fn from(kind: ErrorKind) -> Self {
        Self {
            context: Repr::Simple(kind),
        }
    }
}

impl From<std::io::Error> for Error {
    fn from(error: std::io::Error) -> Self {
        Self::new(ErrorKind::Io, error)
    }
}

impl From<std::str::ParseBoolError> for Error {
    fn from(error: std::str::ParseBoolError) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

impl From<std::num::ParseIntError> for Error {
    fn from(error: std::num::ParseIntError) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

impl From<base64::DecodeError> for Error {
    fn from(error: base64::DecodeError) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

#[cfg(feature = "json")]
impl From<serde_json::Error> for Error {
    fn from(error: serde_json::Error) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

impl From<std::string::FromUtf8Error> for Error {
    fn from(error: std::string::FromUtf8Error) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

impl From<std::str::Utf8Error> for Error {
    fn from(error: std::str::Utf8Error) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

impl From<url::ParseError> for Error {
    fn from(error: url::ParseError) -> Self {
        Self::new(ErrorKind::DataConversion, error)
    }
}

impl From<core::convert::Infallible> for Error {
    fn from(_: core::convert::Infallible) -> Self {
        panic!("no error")
    }
}

impl Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match &self.context {
            Repr::Simple(kind) => std::fmt::Display::fmt(&kind, f),
            Repr::SimpleMessage(_, message) => f.write_str(message),
            Repr::Custom(Custom { error, .. }) => std::fmt::Display::fmt(&error, f),
            Repr::CustomMessage(_, message) => f.write_str(message),
        }
    }
}

/// An extension to the [`Result`] type that easy allows creating [`Error`] values from existing errors.
///
/// This trait cannot be implemented on custom types and is meant for usage with `Result`.
pub trait ResultExt<T>: private::Sealed {
    /// Creates a new error with the specified [`ErrorKind`].
    fn with_kind(self, kind: ErrorKind) -> Result<T>
    where
        Self: Sized;

    /// Creates a new error with the specified [`ErrorKind`] and an additional message.
    fn with_context<C>(self, kind: ErrorKind, message: C) -> Result<T>
    where
        Self: Sized,
        C: Into<Cow<'static, str>>;

    /// Creates a new error with the specified [`ErrorKind`] and a function that returns an additional message.
    fn with_context_fn<F, C>(self, kind: ErrorKind, f: F) -> Result<T>
    where
        Self: Sized,
        F: FnOnce() -> C,
        C: Into<Cow<'static, str>>;
}

mod private {
    pub trait Sealed {}

    impl<T, E> Sealed for std::result::Result<T, E> where E: std::error::Error + Send + Sync + 'static {}
}

impl<T, E> ResultExt<T> for std::result::Result<T, E>
where
    E: std::error::Error + Send + Sync + 'static,
{
    fn with_kind(self, kind: ErrorKind) -> Result<T>
    where
        Self: Sized,
    {
        self.map_err(|e| Error::new(kind, e))
    }

    fn with_context<C>(self, kind: ErrorKind, message: C) -> Result<T>
    where
        Self: Sized,
        C: Into<Cow<'static, str>>,
    {
        self.map_err(|e| Error {
            context: Repr::CustomMessage(
                Custom {
                    error: Box::new(e),
                    kind,
                },
                message.into(),
            ),
        })
    }

    fn with_context_fn<F, C>(self, kind: ErrorKind, f: F) -> Result<T>
    where
        Self: Sized,
        F: FnOnce() -> C,
        C: Into<Cow<'static, str>>,
    {
        self.with_context(kind, f())
    }
}

#[derive(Debug)]
enum Repr {
    Simple(ErrorKind),
    SimpleMessage(ErrorKind, Cow<'static, str>),
    Custom(Custom),
    CustomMessage(Custom, Cow<'static, str>),
}

#[derive(Debug)]
struct Custom {
    kind: ErrorKind,
    error: Box<dyn std::error::Error + Send + Sync>,
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::io;

    #[allow(
        dead_code,
        unconditional_recursion,
        clippy::extra_unused_type_parameters
    )]
    fn ensure_send<T: Send>() {
        ensure_send::<Error>();
    }

    #[derive(thiserror::Error, Debug)]
    enum IntermediateError {
        #[error("second error")]
        Io(#[from] std::io::Error),
    }

    fn create_error() -> Error {
        // Create a nested std::io::Error
        let inner = io::Error::new(io::ErrorKind::BrokenPipe, "third error");
        let inner: IntermediateError = inner.into();
        let inner = io::Error::new(io::ErrorKind::ConnectionAborted, inner);

        // Wrap that io::Error in this crate's Error type
        Error::new(ErrorKind::Io, inner)
    }

    #[test]
    fn errors_display_properly() {
        let error = create_error();

        // Generate the display and error chain
        let mut error: &dyn std::error::Error = &error;
        let display = format!("{error}");
        let mut errors = vec![];
        while let Some(cause) = error.source() {
            errors.push(format!("{cause}"));
            error = cause;
        }

        assert_eq!(display, "second error");
        assert_eq!(errors.join(","), "second error,third error");

        let inner = io::Error::new(io::ErrorKind::BrokenPipe, "third error");
        let error: Result<()> = std::result::Result::<(), std::io::Error>::Err(inner)
            .with_context(ErrorKind::Io, "oh no broken pipe!");
        assert_eq!(format!("{}", error.unwrap_err()), "oh no broken pipe!");
    }

    #[test]
    fn downcasting_works() {
        let error = &create_error() as &dyn std::error::Error;
        assert!(error.is::<Error>());
        let downcasted = error
            .source()
            .unwrap()
            .downcast_ref::<std::io::Error>()
            .unwrap();
        assert_eq!(format!("{downcasted}"), "second error");
    }

    #[test]
    fn turn_into_inner_error() {
        let error = create_error();
        let inner = error.into_inner().unwrap();
        let inner = inner.downcast_ref::<std::io::Error>().unwrap();
        assert_eq!(format!("{inner}"), "second error");

        let error = create_error();
        let inner = error.get_ref().unwrap();
        let inner = inner.downcast_ref::<std::io::Error>().unwrap();
        assert_eq!(format!("{inner}"), "second error");

        let mut error = create_error();
        let inner = error.get_mut().unwrap();
        let inner = inner.downcast_ref::<std::io::Error>().unwrap();
        assert_eq!(format!("{inner}"), "second error");
    }

    #[test]
    fn set_result_kind() {
        let result = std::result::Result::<(), _>::Err(create_error());
        let result = result.with_kind(ErrorKind::Io);
        assert_eq!(&ErrorKind::Io, result.unwrap_err().kind());
    }
}