use std::error::Error as StdError;
use std::fmt;
use std::mem;
use std::result;

pub type StdResult<T> = result::Result<T, Box<dyn std::error::Error>>;
pub type Result<T> = result::Result<T, Error>;

#[derive(Debug)]
pub struct Error {
    repr: Repr,
}

enum Repr {
    Simple(ErrorKind),
    Custom(Box<Custom>),
}

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

#[derive(Debug, Clone)]
pub enum ErrorKind {
    MissedEnvVar(String),
}

impl fmt::Display for ErrorKind {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            ErrorKind::MissedEnvVar(ref name) => {
                write!(fmt, r#"Missed "{}" environment variable"#, name)
            }
        }
    }
}

impl PartialEq for ErrorKind {
    fn eq(&self, other: &Self) -> bool {
        mem::discriminant(self) == mem::discriminant(other)
    }
}

impl From<ErrorKind> for Error {
    #[inline]
    fn from(kind: ErrorKind) -> Error {
        Error {
            repr: Repr::Simple(kind),
        }
    }
}

impl Error {
    pub fn new<E>(kind: ErrorKind, error: E) -> Error
    where
        E: Into<Box<dyn StdError + Send + Sync>>,
    {
        Self::_new(kind, error.into())
    }

    fn _new(kind: ErrorKind, error: Box<dyn StdError + Send + Sync>) -> Error {
        Error {
            repr: Repr::Custom(Box::new(Custom { kind, error })),
        }
    }

    pub fn kind(&self) -> &ErrorKind {
        match &self.repr {
            Repr::Custom(ref c) => &c.kind,
            Repr::Simple(kind) => &kind,
        }
    }
}

impl fmt::Debug for Repr {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Repr::Custom(ref c) => fmt::Debug::fmt(&c, fmt),
            Repr::Simple(kind) => fmt.debug_tuple("Kind").field(&kind).finish(),
        }
    }
}

impl fmt::Display for Error {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self.repr {
            Repr::Custom(ref c) => c.error.fmt(fmt),
            Repr::Simple(kind) => write!(fmt, "{}", kind),
        }
    }
}

impl StdError for Error {
    fn source(&self) -> Option<&(dyn StdError + 'static)> {
        match self.repr {
            Repr::Simple(..) => None,
            Repr::Custom(ref c) => c.error.source(),
        }
    }
}