// This is a part of Chrono.

// See README.md and LICENSE.txt for details.

//! ISO 8601 week.

use core::fmt;

use super::internals::YearFlags;

#[cfg(any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"))]

use rkyv::{Archive, Deserialize, Serialize};

/// ISO 8601 week.

///

/// This type, combined with [`Weekday`](../enum.Weekday.html),

/// constitutes the ISO 8601 [week date](./struct.NaiveDate.html#week-date).

/// One can retrieve this type from the existing [`Datelike`](../trait.Datelike.html) types

/// via the [`Datelike::iso_week`](../trait.Datelike.html#tymethod.iso_week) method.

#[derive(PartialEq, Eq, PartialOrd, Ord, Copy, Clone, Hash)]

#[cfg_attr(

    any(feature = "rkyv", feature = "rkyv-16", feature = "rkyv-32", feature = "rkyv-64"),

    derive(Archive, Deserialize, Serialize),

    archive(compare(PartialEq, PartialOrd)),

    archive_attr(derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash))

)]

#[cfg_attr(feature = "rkyv-validation", archive(check_bytes))]

pub struct IsoWeek {

    // Note that this allows for larger year range than `NaiveDate`.

    // This is crucial because we have an edge case for the first and last week supported,

    // which year number might not match the calendar year number.

    ywf: i32, // (year << 10) | (week << 4) | flag

}

impl IsoWeek {

    /// Returns the corresponding `IsoWeek` from the year and the `Of` internal value.

    //

    // Internal use only. We don't expose the public constructor for `IsoWeek` for now

    // because the year range for the week date and the calendar date do not match, and

    // it is confusing to have a date that is out of range in one and not in another.

    // Currently we sidestep this issue by making `IsoWeek` fully dependent of `Datelike`.

    pub(super) fn from_yof(year: i32, ordinal: u32, year_flags: YearFlags) -> Self {

        let rawweek = (ordinal + year_flags.isoweek_delta()) / 7;

        let (year, week) = if rawweek < 1 {

            // previous year

            let prevlastweek = YearFlags::from_year(year - 1).nisoweeks();

            (year - 1, prevlastweek)

        } else {

            let lastweek = year_flags.nisoweeks();

            if rawweek > lastweek {

                // next year

                (year + 1, 1)

            } else {

                (year, rawweek)

            }

        };

        let flags = YearFlags::from_year(year);

        IsoWeek { ywf: (year << 10) | (week << 4) as i32 | i32::from(flags.0) }

    }

    /// Returns the year number for this ISO week.

    ///

    /// # Example

    ///

    /// ```

    /// use chrono::{Datelike, NaiveDate, Weekday};

    ///

    /// let d = NaiveDate::from_isoywd_opt(2015, 1, Weekday::Mon).unwrap();

    /// assert_eq!(d.iso_week().year(), 2015);

    /// ```

    ///

    /// This year number might not match the calendar year number.

    /// Continuing the example...

    ///

    /// ```

    /// # use chrono::{NaiveDate, Datelike, Weekday};

    /// # let d = NaiveDate::from_isoywd_opt(2015, 1, Weekday::Mon).unwrap();

    /// assert_eq!(d.year(), 2014);

    /// assert_eq!(d, NaiveDate::from_ymd_opt(2014, 12, 29).unwrap());

    /// ```

    #[inline]

    pub const fn year(&self) -> i32 {

        self.ywf >> 10

    }

    /// Returns the ISO week number starting from 1.

    ///

    /// The return value ranges from 1 to 53. (The last week of year differs by years.)

    ///

    /// # Example

    ///

    /// ```

    /// use chrono::{Datelike, NaiveDate, Weekday};

    ///

    /// let d = NaiveDate::from_isoywd_opt(2015, 15, Weekday::Mon).unwrap();

    /// assert_eq!(d.iso_week().week(), 15);

    /// ```

    #[inline]

    pub const fn week(&self) -> u32 {

        ((self.ywf >> 4) & 0x3f) as u32

    }

    /// Returns the ISO week number starting from 0.

    ///

    /// The return value ranges from 0 to 52. (The last week of year differs by years.)

    ///

    /// # Example

    ///

    /// ```

    /// use chrono::{Datelike, NaiveDate, Weekday};

    ///

    /// let d = NaiveDate::from_isoywd_opt(2015, 15, Weekday::Mon).unwrap();

    /// assert_eq!(d.iso_week().week0(), 14);

    /// ```

    #[inline]

    pub const fn week0(&self) -> u32 {

        ((self.ywf >> 4) & 0x3f) as u32 - 1

    }

}

/// The `Debug` output of the ISO week `w` is the same as

/// [`d.format("%G-W%V")`](../format/strftime/index.html)

/// where `d` is any `NaiveDate` value in that week.

///

/// # Example

///

/// ```

/// use chrono::{Datelike, NaiveDate};

///

/// assert_eq!(

///     format!("{:?}", NaiveDate::from_ymd_opt(2015, 9, 5).unwrap().iso_week()),

///     "2015-W36"

/// );

/// assert_eq!(format!("{:?}", NaiveDate::from_ymd_opt(0, 1, 3).unwrap().iso_week()), "0000-W01");

/// assert_eq!(

///     format!("{:?}", NaiveDate::from_ymd_opt(9999, 12, 31).unwrap().iso_week()),

///     "9999-W52"

/// );

/// ```

///

/// ISO 8601 requires an explicit sign for years before 1 BCE or after 9999 CE.

///

/// ```

/// # use chrono::{NaiveDate, Datelike};

/// assert_eq!(format!("{:?}", NaiveDate::from_ymd_opt(0, 1, 2).unwrap().iso_week()), "-0001-W52");

/// assert_eq!(

///     format!("{:?}", NaiveDate::from_ymd_opt(10000, 12, 31).unwrap().iso_week()),

///     "+10000-W52"

/// );

/// ```

impl fmt::Debug for IsoWeek {

    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

        let year = self.year();

        let week = self.week();

        if (0..=9999).contains(&year) {

            write!(f, "{year:04}-W{week:02}")

        } else {

            // ISO 8601 requires the explicit sign for out-of-range years

            write!(f, "{year:+05}-W{week:02}")

        }

    }

}

#[cfg(test)]

mod tests {

    #[cfg(feature = "rkyv-validation")]

    use super::IsoWeek;

    use crate::Datelike;

    use crate::naive::date::{self, NaiveDate};

    #[test]

    fn test_iso_week_extremes() {

        let minweek = NaiveDate::MIN.iso_week();

        let maxweek = NaiveDate::MAX.iso_week();

        assert_eq!(minweek.year(), date::MIN_YEAR);

        assert_eq!(minweek.week(), 1);

        assert_eq!(minweek.week0(), 0);

        #[cfg(feature = "alloc")]

        assert_eq!(format!("{minweek:?}"), NaiveDate::MIN.format("%G-W%V").to_string());

        assert_eq!(maxweek.year(), date::MAX_YEAR + 1);

        assert_eq!(maxweek.week(), 1);

        assert_eq!(maxweek.week0(), 0);

        #[cfg(feature = "alloc")]

        assert_eq!(format!("{maxweek:?}"), NaiveDate::MAX.format("%G-W%V").to_string());

    }

    #[test]

    fn test_iso_week_equivalence_for_first_week() {

        let monday = NaiveDate::from_ymd_opt(2024, 12, 30).unwrap();

        let friday = NaiveDate::from_ymd_opt(2025, 1, 3).unwrap();

        assert_eq!(monday.iso_week(), friday.iso_week());

    }

    #[test]

    fn test_iso_week_equivalence_for_last_week() {

        let monday = NaiveDate::from_ymd_opt(2026, 12, 28).unwrap();

        let friday = NaiveDate::from_ymd_opt(2027, 1, 1).unwrap();

        assert_eq!(monday.iso_week(), friday.iso_week());

    }

    #[test]

    fn test_iso_week_ordering_for_first_week() {

        let monday = NaiveDate::from_ymd_opt(2024, 12, 30).unwrap();

        let friday = NaiveDate::from_ymd_opt(2025, 1, 3).unwrap();

        assert!(monday.iso_week() >= friday.iso_week());

        assert!(monday.iso_week() <= friday.iso_week());

    }

    #[test]

    fn test_iso_week_ordering_for_last_week() {

        let monday = NaiveDate::from_ymd_opt(2026, 12, 28).unwrap();

        let friday = NaiveDate::from_ymd_opt(2027, 1, 1).unwrap();

        assert!(monday.iso_week() >= friday.iso_week());

        assert!(monday.iso_week() <= friday.iso_week());

    }

    #[test]

    #[cfg(feature = "rkyv-validation")]

    fn test_rkyv_validation() {

        let minweek = NaiveDate::MIN.iso_week();

        let bytes = rkyv::to_bytes::<_, 4>(&minweek).unwrap();

        assert_eq!(rkyv::from_bytes::<IsoWeek>(&bytes).unwrap(), minweek);

        let maxweek = NaiveDate::MAX.iso_week();

        let bytes = rkyv::to_bytes::<_, 4>(&maxweek).unwrap();

        assert_eq!(rkyv::from_bytes::<IsoWeek>(&bytes).unwrap(), maxweek);

    }

}