use crate::Pronoun;

use time::{Date, Month, OffsetDateTime};

/// The start of the COVID-19 lockdowns
///
/// This is used as an epoch in order to convert from a given date to an integer seed.  This is
/// specified as part of the algorithm for randomly selecting from a weighted list.
pub const COVID_EPOCH: Date = match Date::from_calendar_date(2020, Month::January, 26) {
	Ok(d) => d,
	Err(_) => Date::MIN, // This never runs, but we can't unwrap, so this is what we're stuck with
};

/// A list of pronouns and their associated weights, used for random selection
///
/// Weights are typically representative of a user's preference towards a pronoun.  A pronoun with
/// a weight of 10 is twice as likely to be selected as a pronoun with a weight of 5.
///
/// This struct is use to represent these weights before they are used to randomly select a
/// pronoun.  Additional methods are provided to perform this random selection on a weighted list,
/// using as a seed both an arbitrary string of bytes and a Date.
pub struct WeightedTable<'a>(pub Vec<(&'a Pronoun, u8)>);

impl<'a> WeightedTable<'a> {

	/// A shorthand for calling [`WeightedTable::select_on_date()`] with today's date
	///
	/// The date is generated for the system's time and timezone
	pub fn select_today(&self, seed: &[u8]) -> &Pronoun {
		self.select_on_date(
			seed,
			OffsetDateTime::now_local()
				.unwrap_or_else(|_| OffsetDateTime::now_utc())
				.date()
		)
	}

	/// Randomly select a pronoun set for a given date and name.
	///
	/// Is a wrapper for calling [`WeightedTable::select`] with the given date mixed into the seed.
	pub fn select_on_date(&self, seed: &[u8], date: Date) -> &Pronoun {
		let mut new_seed: Vec<u8> = Vec::with_capacity(seed.len() + 4);
		new_seed.extend(
			(
				(date - COVID_EPOCH)
				.whole_days()
				as u32
			).to_le_bytes()
		);
		new_seed.extend(seed);
		self.select(seed.as_ref())
	}

	/// Randomly select a pronoun set for a given seed
	///
	/// This function is *pure*, and any randomness is produced internally using PRNG seeded with
	/// the given date and seed.  That is to say, for any given seed, this table must always
	/// produce the same pronoun set.
	pub fn select(&self, seed: &[u8]) -> &Pronoun {
		todo!()
	}

}