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use crate::{Date, InvalidDayOfMonth};

/// Extension for `Result<Date>` to round invalid dates.
pub trait DateResultExt {
	/// Get the date or the next valid date.
	///
	/// This function gives the first day of the next month for the invalid date.
	/// It ignores any excess days in the invalid date.
	fn or_next_valid(&self) -> Date;

	/// Get the date or the next valid date.
	///
	/// This function gives the last day of the current month for the invalid date.
	/// It ignores any excess days in the invalid date.
	fn or_prev_valid(&self) -> Date;
}

impl DateResultExt for Result<Date, InvalidDayOfMonth> {
	fn or_next_valid(&self) -> Date {
		self.unwrap_or_else(|e| e.next_valid())
	}

	fn or_prev_valid(&self) -> Date {
		self.unwrap_or_else(|e| e.prev_valid())
	}
}

#[cfg(test)]
mod test {
	use super::*;
	use assert2::assert;

	#[test]
	fn or_next_prev_valid() {
		assert!(Date::new(2020, 1, 31).unwrap().add_months(2).or_next_valid() == Date::new(2020, 3, 31).unwrap());
		assert!(Date::new(2020, 1, 31).unwrap().add_months(1).or_next_valid() == Date::new(2020, 3, 1).unwrap());
		assert!(Date::new(2020, 1, 31).unwrap().add_months(1).or_prev_valid() == Date::new(2020, 2, 29).unwrap());
	}
}