whatwg-datetime 0.1.1

use crate::tokens::TOKEN_HYPHEN;
use crate::utils::{collect_ascii_digits, is_valid_month};
use crate::{collect_month_and_validate, parse_format};

/// A [proleptic-Gregorian date][proleptic-greg] consisting of a year and a month,
/// with no time-zone or date information.
///
/// # Examples
/// ```
/// use whatwg_datetime::{parse_month, YearMonth};
///
/// assert_eq!(parse_month("2011-11"), YearMonth::new_opt(2011, 11));
/// ```
///
/// [proleptic-greg]: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#proleptic-gregorian-date
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub struct YearMonth {
	pub(crate) year: i32,
	pub(crate) month: u32,
}

impl YearMonth {
	pub(crate) const fn new(year: i32, month: u32) -> Self {
		Self { year, month }
	}

	/// Creates a new `YearMonth` from a year and a month number.
	///
	/// This asserts that:
	/// - the year is greater than 0
	/// - that the month number is between 1 and 12, inclusive
	///
	/// # Examples
	/// ```
	/// use whatwg_datetime::YearMonth;
	///
	/// assert!(YearMonth::new_opt(2011, 11).is_some());
	/// assert!(YearMonth::new_opt(2011, 0).is_none()); // Month number must be at least 1
	/// assert!(YearMonth::new_opt(0, 1).is_none()); // Year number must be greater than 0
	/// ```
	pub fn new_opt(year: i32, month: u32) -> Option<Self> {
		if year == 0 {
			return None;
		}

		if !is_valid_month(&month) {
			return None;
		}

		Some(Self::new(year, month))
	}

	/// A year component. This is a number greater than 0.
	///
	/// # Examples
	/// ```
	/// use whatwg_datetime::YearMonth;
	///
	/// let year_month = YearMonth::new_opt(2011, 11).unwrap();
	/// assert_eq!(year_month.year(), 2011);
	/// ```
	#[inline]
	pub const fn year(&self) -> i32 {
		self.year
	}

	/// A month component. This is a number from 1 to 12, inclusive.
	///
	/// # Examples
	/// ```
	/// use whatwg_datetime::YearMonth;
	///
	/// let year_month = YearMonth::new_opt(2011, 11).unwrap();
	/// assert_eq!(year_month.month(), 11);
	/// ```
	#[inline]
	pub const fn month(&self) -> u32 {
		self.month
	}
}

/// Parse a [proleptic-Gregorian date][proleptic-greg] consisting of a year and a month,
/// with no time-zone or date information
///
/// This follows the rules for [parsing a month string][whatwg-html-parse]
/// per [WHATWG HTML Standard § 2.3.5.1 Months][whatwg-html-months].
///
/// # Examples
/// ```
/// use whatwg_datetime::{parse_month, YearMonth};
///
/// assert_eq!(parse_month("2011-11"), YearMonth::new_opt(2011, 11));
/// ```
///
/// [proleptic-greg]: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#proleptic-gregorian-date
/// [whatwg-html-months]: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#months
/// [whatwg-html-parse]: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-month-string
#[inline]
pub fn parse_month(s: &str) -> Option<YearMonth> {
	parse_format(s, parse_month_component)
}

/// Low-level function for parsing an individual month component at a given position
///
/// This follows the rules for [parsing a month component][whatwg-html-parse]
/// per [WHATWG HTML Standard § 2.3.5.1 Months][whatwg-html-months].
///
/// > **Note**:
/// > This function exposes a lower-level API than [`parse_month`]. More than likely,
/// > you will want to use [`parse_month`] instead.
///
/// # Examples
/// ```
/// use whatwg_datetime::{parse_month_component, YearMonth};
///
/// let mut position = 0usize;
/// let date = parse_month_component("2011-11", &mut position);
///
/// assert_eq!(date, YearMonth::new_opt(2011, 11));
/// ```
///
/// [whatwg-html-months]: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#months
/// [whatwg-html-parse]: https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#parse-a-month-component
pub fn parse_month_component(s: &str, position: &mut usize) -> Option<YearMonth> {
	let parsed_year = collect_ascii_digits(s, position);
	if parsed_year.len() < 4 {
		return None;
	}

	let year = parsed_year.parse::<i32>().ok()?;
	if year == 0 {
		return None;
	}

	if *position > s.len() || s.chars().nth(*position) != Some(TOKEN_HYPHEN) {
		return None;
	} else {
		*position += 1;
	}

	let month = collect_month_and_validate(s, position)?;
	Some(YearMonth::new(year, month))
}

#[cfg(test)]
mod tests {
	use super::{parse_month, parse_month_component, YearMonth};

	#[test]
	fn test_parse_month_string() {
		let parsed = parse_month("2004-12");
		assert_eq!(parsed, Some(YearMonth::new(2004, 12)));
	}

	#[test]
	fn test_parse_month_string_fails_invalid_month() {
		let parsed = parse_month("2004-2a");
		assert_eq!(parsed, None);
	}

	#[test]
	fn test_parse_month_string_fails() {
		let parsed = parse_month("2004-13");
		assert_eq!(parsed, None);
	}

	#[test]
	fn test_parse_month_component() {
		let mut position = 0usize;
		let parsed = parse_month_component("2004-12", &mut position);

		assert_eq!(parsed, Some(YearMonth::new(2004, 12)));
	}

	#[test]
	fn test_parse_month_component_fails_year_lt_4_digits() {
		let mut position = 0usize;
		let parsed = parse_month_component("200-12", &mut position);

		assert_eq!(parsed, None);
	}

	#[test]
	fn test_parse_month_component_fails_invalid_month_lower_bound() {
		let mut position = 0usize;
		let parsed = parse_month_component("2004-0", &mut position);

		assert_eq!(parsed, None);
	}

	#[test]
	fn test_parse_month_component_fails_invalid_month_upper_bound() {
		let mut position = 0usize;
		let parsed = parse_month_component("2004-13", &mut position);

		assert_eq!(parsed, None);
	}

	#[test]
	fn test_parse_month_component_fails_invalid_month_syntax() {
		let mut position = 0usize;
		let parsed = parse_month_component("2004-1a", &mut position);

		assert_eq!(parsed, None);
	}

	#[test]
	fn test_parse_month_component_fails_invalid_separator() {
		let mut position = 0usize;
		let parsed = parse_month_component("2004/12", &mut position);

		assert_eq!(parsed, None);
	}
}