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use core::fmt;

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum TryAddError {
    DegreeOutOfBounds,
    TooManyTerms,
    CanNotNegate,
}

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum TermFromStringError {
    MoreThanOneX,
    CoeffCouldNotBeParsed,
    UnexpectedChar(char),
    CaretWithoutXInFront,
    CaretWithoutDegree,
    MultipleCarets,
    DegreeCouldNotBeParsed,
}

#[derive(Debug, Copy, Clone, Eq, PartialEq)]
pub enum PolynomialFromStringError {
    TermFromString(TermFromStringError),
    AddingTerm(TryAddError),
    NoTermsFound,
}

impl fmt::Display for TermFromStringError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            TermFromStringError::MoreThanOneX => write!(f, "More than one occurance of 'x' in str"),
            TermFromStringError::CoeffCouldNotBeParsed => write!(f, "Coeff could not be parsed."),
            TermFromStringError::CaretWithoutXInFront => write!(f, "^ seen without x in front"),
            TermFromStringError::UnexpectedChar(c) => write!(
                f,
                "Unexpected char ({}) (legal characters include +, -, ., x, ^, 0..9).",
                c
            ),
            TermFromStringError::MultipleCarets => write!(f, "^ appears more than once."),
            TermFromStringError::CaretWithoutDegree => write!(f, "^ without ensuing degree!"),
            TermFromStringError::DegreeCouldNotBeParsed => write!(f, "Degree could not be parsed"),
        }
    }
}