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use std::{error::Error as StdError, fmt, io};

use crate::SharedString;

/// A boxed error
pub type BoxedError = Box<dyn std::error::Error + Send + Sync + 'static>;

#[derive(Debug)]
pub(crate) enum ErrorKind {
    /// An asset without extension was loaded.
    NoDefaultValue,

    /// An I/O error occured.
    Io(io::Error),

    /// The conversion from raw bytes failed.
    Conversion(BoxedError),

    /// Failed to load another asset
    Other(BoxedError),
}

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

impl From<BoxedError> for ErrorKind {
    fn from(err: BoxedError) -> Self {
        Self::Conversion(err)
    }
}

impl ErrorKind {
    pub fn or(self, other: Self) -> Self {
        use ErrorKind::*;

        match (self, other) {
            (NoDefaultValue, other) => other,
            (Io(_), other @ Conversion(_)) => other,
            (Io(err), other @ Io(_)) if err.kind() == io::ErrorKind::NotFound => other,
            (this, _) => this,
        }
    }
}

#[derive(Debug)]
struct NoDefaultValueError;

impl fmt::Display for NoDefaultValueError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str("the asset has neither extension nor default value")
    }
}

impl StdError for NoDefaultValueError {}

struct ErrorRepr {
    id: SharedString,
    kind: ErrorKind,
}

/// The error type which is used when loading an asset.
pub struct Error(Box<ErrorRepr>);

impl Error {
    #[cold]
    pub(crate) fn from_io(id: SharedString, err: io::Error) -> Self {
        Self::from_kind(id, ErrorKind::Io(err))
    }

    pub(crate) fn from_kind(id: SharedString, kind: ErrorKind) -> Self {
        Self(Box::new(ErrorRepr { id, kind }))
    }

    #[cold]
    pub(crate) fn new(id: SharedString, err: BoxedError) -> Self {
        Self::from_kind(id, ErrorKind::Other(err))
    }

    /// The id of the asset that was being loaded when the error happened.
    #[inline]
    pub fn id(&self) -> &SharedString {
        &self.0.id
    }

    /// Like `source`, but never fails
    pub fn reason(&self) -> &(dyn StdError + 'static) {
        match &self.0.kind {
            ErrorKind::Io(err) => err,
            ErrorKind::Conversion(err) | ErrorKind::Other(err) => &**err,
            ErrorKind::NoDefaultValue => &NoDefaultValueError,
        }
    }
}

impl fmt::Debug for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Error")
            .field("id", &self.0.id)
            .field("kind", &self.0.kind)
            .finish()
    }
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_fmt(format_args!("failed to load \"{}\"", self.id()))
    }
}

impl std::error::Error for Error {
    #[inline]
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        Some(self.reason())
    }
}