use std::error;
use std::fmt;

/// An error that can occur in this crate.
///
/// Generally, this error corresponds to problems building a regular
/// expression, whether it's in parsing, compilation or a problem with
/// guaranteeing a configured optimization.
#[derive(Clone, Debug)]
pub struct Error {
    kind: ErrorKind,
}

impl Error {
    pub(crate) fn regex<E: error::Error>(err: E) -> Error {
        Error { kind: ErrorKind::Regex(err.to_string()) }
    }

    /// Return the kind of this error.
    pub fn kind(&self) -> &ErrorKind {
        &self.kind
    }
}

/// The kind of an error that can occur.
#[derive(Clone, Debug)]
pub enum ErrorKind {
    /// An error that occurred as a result of parsing a regular expression.
    /// This can be a syntax error or an error that results from attempting to
    /// compile a regular expression that is too big.
    ///
    /// The string here is the underlying error converted to a string.
    Regex(String),
    /// Hints that destructuring should not be exhaustive.
    ///
    /// This enum may grow additional variants, so this makes sure clients
    /// don't count on exhaustive matching. (Otherwise, adding a new variant
    /// could break existing code.)
    #[doc(hidden)]
    __Nonexhaustive,
}

impl error::Error for Error {
    fn description(&self) -> &str {
        match self.kind {
            ErrorKind::Regex(_) => "regex error",
            ErrorKind::__Nonexhaustive => unreachable!(),
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self.kind {
            ErrorKind::Regex(ref s) => write!(f, "{}", s),
            ErrorKind::__Nonexhaustive => unreachable!(),
        }
    }
}