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/// The error type for operations in Gurobi Rust API
#[derive(Debug, Eq, PartialEq)]
pub enum Error {
    /// An error returned from Gurobi C API.  Contains the message and the error code.
    FromAPI(String, i32),
    /// Conversion to a C-style null-termined string failed.  Contains the underlying [`std::ffi::NulError`].
    NulError(std::ffi::NulError),
    /// Query/modifying a removed variable or constraint
    ModelObjectRemoved,
    /// Model object hasn't been updated yet.  A call to [`Model::update`](crate::Model::update) is needed.
    ModelObjectPending,
    /// Model object comes from a different model
    ModelObjectMismatch,
    /// A call to [`Model::update`](crate::Model::update) is required before this operation
    ModelUpdateNeeded,
    /// Modelling errors caused by the user, usually by providing quadratic expressions to methods that expect
    /// linear terms such as [`Model::add_constr`](crate::Model::add_constr).
    AlgebraicError(String),
    /// Gurobi feature not yet supported by this crate. Currently for internal use only.
    NotYetSupported(String),
}

impl From<std::ffi::NulError> for Error {
    fn from(err: std::ffi::NulError) -> Error {
        Error::NulError(err)
    }
}

impl std::fmt::Display for Error {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            Error::FromAPI(message, code) => write!(f, "Error from API: {} ({})", message, code),
            Error::NulError(err) => f.write_fmt(format_args!("NulError: {}", err)),
            Error::ModelObjectRemoved => {
                f.write_str("Variable or constraint has been removed from the model")
            }
            Error::ModelObjectPending => {
                f.write_str("Variable or constraint is awaiting model update")
            }
            Error::ModelObjectMismatch => {
                f.write_str("Variable or constraint is part of a different model")
            }
            Error::ModelUpdateNeeded => f.write_str(
                "Variables or constraints have been added/removed.  Call model.update() first.",
            ),
            Error::AlgebraicError(s) => f.write_fmt(format_args!("Algebraic error: {}", s)),
            Error::NotYetSupported(s) => f.write_fmt(format_args!("Not yet supported: {}", s)),
        }
    }
}

impl std::error::Error for Error {}

/// A specialized [`std::result::Result`] for library errors
pub type Result<T> = std::result::Result<T, Error>;