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use std::io;
use std::borrow::Cow;
use std::fmt;
use std::error;
use std::str;

use util;
use common::{Position, TextPosition};

#[derive(Debug)]
pub enum ErrorKind {
    Syntax(Cow<'static, str>),
    Io(io::Error),
    Utf8(str::Utf8Error),
    UnexpectedEof,
}

/// An XML parsing error.
///
/// Consists of a 2D position in a document and a textual message describing the error.
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct Error {
    pos: TextPosition,
    kind: ErrorKind,
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{} {}", self.pos, self.msg())
    }
}

impl Position for Error {
    #[inline]
    fn position(&self) -> TextPosition { self.pos }
}

impl Error {
    /// Returns a reference to a message which is contained inside this error.
    #[inline]
    pub fn msg(&self) -> &str {
        use self::ErrorKind::*;
        match self.kind {
            UnexpectedEof => &"Unexpected EOF",
            Utf8(ref reason) => error_description(reason),
            Io(ref io_error) => error_description(io_error),
            Syntax(ref msg) => msg.as_ref(),
        }
    }

    pub fn kind(&self) -> &ErrorKind { &self.kind }
}

impl error::Error for Error {
    #[inline]
    fn description(&self) -> &str { self.msg() }
}

impl<'a, P, M> From<(&'a P, M)> for Error where P: Position, M: Into<Cow<'static, str>> {
    fn from(orig: (&'a P, M)) -> Self {
        Error{
            pos: orig.0.position(),
            kind: ErrorKind::Syntax(orig.1.into())
        }
    }
}

impl From<util::CharReadError> for Error {
    fn from(e: util::CharReadError) -> Self {
        use util::CharReadError::*;
        Error{
            pos: TextPosition::new(),
            kind: match e {
                UnexpectedEof => ErrorKind::UnexpectedEof,
                Utf8(reason) => ErrorKind::Utf8(reason),
                Io(io_error) => ErrorKind::Io(io_error),
            }
        }
    }
}

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

impl Clone for ErrorKind {
    fn clone(&self) -> Self {
        use self::ErrorKind::*;
        match *self {
            UnexpectedEof => UnexpectedEof,
            Utf8(ref reason) => Utf8(reason.clone()),
            Io(ref io_error) => Io(io::Error::new(io_error.kind(), error_description(io_error))),
            Syntax(ref msg) => Syntax(msg.clone()),
        }
    }
}
impl PartialEq for ErrorKind {
    fn eq(&self, other: &ErrorKind) -> bool {
        use self::ErrorKind::*;
        match (self, other) {
            (&UnexpectedEof, &UnexpectedEof) => true,
            (&Utf8(ref left), &Utf8(ref right)) => left == right,
            (&Io(ref left), &Io(ref right)) =>
                left.kind() == right.kind() &&
                error_description(left) == error_description(right),
            (&Syntax(ref left), &Syntax(ref right)) =>
                left == right,

            (_, _) => false,
        }
    }
}
impl Eq for ErrorKind {}

fn error_description(e: &error::Error) -> &str { e.description() }