/// This trait allows a `Model` to be validated.
pub trait Validate {
    /// Validate the `Model`
    fn validate(&self) -> impl std::future::Future<Output = Result<(), String>> + Send;
}

/// Validate a value and return an Error if validation fails.
#[macro_export]
macro_rules! validate {
    ($val:expr) => {
        if let Err(err) = $val.validate().await {
            return Err(format!("{}: {}", stringify!($val), err));
        }
    };
}

#[macro_export]
macro_rules! count_items {
    // Base case: single item
    ($single:ident) => { 1 };
    // Recursive case: count each item
    ($head:ident, $($tail:ident),*) => {
        1 + mongod::count_items!($($tail),*)
    };
}

/// This macro checks for the type of a reference and is useful for validation.
/// It will check all supplied types and return `false` if none are matching.
///
/// # Example
/// ```ignore
/// fn validate(&self) -> bool {
///     assert_reference_of!(self.owner, Person);
///     true
/// }
/// ```
#[macro_export]
macro_rules! assert_reference_of {
    ($var:expr, $($struct_name:ident),+) => {
        let mut match_found = false;
        $(
            if $var.is_of_collection($struct_name::collection_name()) {
                match_found = true;
            }
        )*
        if !match_found {
            let possible_types: [&str; mongod::count_items!($($struct_name),*)] = [
                $(stringify!($struct_name)),*
            ];
            return Err(format!("{} is not of any type: {:?}", stringify!($var), possible_types));
        }
    };
}