pub trait Validation {
    fn validate(&self) -> Result<(), ValidationError>;
}

#[derive(Debug)]
pub struct ValidationError {
    messages: Vec<String>,
}

impl std::fmt::Display for ValidationError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        for msg in &self.messages {
            write!(f, "{}\n", msg)?;
        }
        Ok(())
    }
}

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

pub fn add_results(first: Result<(), ValidationError>, second: Result<(), ValidationError>) -> Result<(), ValidationError> {
    if first.is_ok() && second.is_ok() {
        Ok(())
    } else if first.is_ok() && second.is_err() {
        second
    } else if first.is_err() && second.is_ok() {
        first
    } else {
        let mut first = first.err().unwrap();
        let mut second = second.err().unwrap();
        first.messages.append(&mut second.messages);

        Err( ValidationError{ messages:  first.messages } )
    }
}