error.rs

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use std::fmt;


#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Error {
    pub message: String,
    pub position: usize,
    pub in_font: bool,
}


impl Error {
    pub fn new(message: impl Into<String>, position: usize) -> Error {
        Error {message: message.into(), position, in_font: false}
    }

    pub fn font(message: impl Into<String>, position: usize) -> Error {
        Error {message: message.into(), position, in_font: true}
    }
}


impl fmt::Display for Error {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        let unit = if self.in_font {"byte"} else {"character"};

        write!(formatter, "{} ({unit} {})", self.message, self.position + 1)
    }
}


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


#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn a_font_error_counts_bytes() {
        assert_eq!(Error::new("mistake", 3).to_string(), "mistake (character 4)");
        assert_eq!(Error::font("mistake", 3).to_string(), "mistake (byte 4)");
    }
}