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use std::error;
use std::ffi::NulError;
use std::fmt;
use std::io;
use std::num::TryFromIntError;
use std::result;
use std::str::Utf8Error;

use milter_sys as sys;

/// A result type specialised for milter errors.
pub type Result<T> = result::Result<T, Error>;

/// Errors of different kinds specialised for milters, with source attached if
/// available.
#[derive(Debug)]
pub struct Error {
    kind: ErrorKind,
    error: Option<Box<dyn error::Error + Send + Sync>>,
}

impl Error {
    /// Constructs a new error with the given kind and source.
    pub fn new<E>(kind: ErrorKind, error: E) -> Self
    where
        E: Into<Box<dyn error::Error + Send + Sync>>,
    {
        Error {
            kind,
            error: Some(error.into()),
        }
    }

    /// Returns this error’s kind.
    pub fn kind(&self) -> ErrorKind {
        self.kind
    }
}

impl From<ErrorKind> for Error {
    fn from(kind: ErrorKind) -> Self {
        Error { kind, error: None }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use ErrorKind::*;

        match self.kind {
            SocketConfig => write!(f, "invalid socket configuration"),
            TimeoutConfig => write!(f, "invalid timeout configuration"),
            SocketBacklogConfig => write!(f, "invalid socket backlog configuration"),
            MilterRegistration => write!(f, "failed to register configuration with milter library"),
            MainFailureStatus => write!(f, "milter library main function returned failure status"),
            CallbackPanic => write!(f, "milter library main function exited after callback panic"),
            TypeConversion => write!(f, "failed to convert data type at FFI boundary"),
            FailureStatus => write!(f, "milter library function returned failure status"),
            DataAccess => write!(f, "invalid access of context data"),
            Io => write!(f, "I/O error"),
            _ => write!(f, "unspecified error"),
        }
    }
}

// TODO revisit
impl error::Error for Error {
    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
        Some(&**self.error.as_ref()?)
    }
}

/// Various kinds of errors that can occur in a milter.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub enum ErrorKind {
    /// The socket specification provided to the milter could not be used.
    SocketConfig,
    /// The timeout configuration parameter of `Milter` could not be used.
    TimeoutConfig,
    /// The socket backlog configuration parameter of `Milter` could not be
    /// used.
    SocketBacklogConfig,
    /// Registration of the milter’s configuration with the milter library
    /// failed.
    MilterRegistration,
    /// The milter library’s main event loop exited with a failure status.
    MainFailureStatus,
    /// The milter library’s main event loop exited due to a panic in a
    /// callback.
    CallbackPanic,

    /// Type conversion at the FFI boundary (Rust/C) failed.
    TypeConversion,
    /// A milter library function returned the failure status code.
    FailureStatus,
    /// Erroneous access of context data, such as violation of dynamic borrowing
    /// rules.
    DataAccess,

    /// An I/O error occurred (provided for convenience).
    Io,
    /// An unspecified error occurred (provided for convenience).
    Other,
}

impl From<NulError> for Error {
    fn from(error: NulError) -> Self {
        Error::new(ErrorKind::TypeConversion, error)
    }
}

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

impl From<TryFromIntError> for Error {
    fn from(error: TryFromIntError) -> Self {
        Error::new(ErrorKind::TypeConversion, error)
    }
}

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

// TODO StatusCode? consider renaming ... MilterStatus?

/// Status returned from calls to the milter library.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub(crate) enum StatusCode {
    Success,
    Failure,
}

impl From<i32> for StatusCode {
    fn from(status: i32) -> Self {
        match status {
            sys::MI_SUCCESS => Self::Success,
            sys::MI_FAILURE => Self::Failure,
            _ => panic!("unknown return status code {}", status),
        }
    }
}

impl From<StatusCode> for Result<()> {
    fn from(status_code: StatusCode) -> Self {
        match status_code {
            StatusCode::Success => Ok(()),
            StatusCode::Failure => Err(Error::from(ErrorKind::FailureStatus)),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::error::Error as EError;

    #[test]
    fn source_error() {
        let e = Error::from(ErrorKind::TypeConversion);

        assert!(e.source().is_none());
    }
}