month_end.rs

use arrow::legacy::time_zone::Tz;
use chrono::NaiveDateTime;
use polars_core::prelude::*;
use polars_core::utils::arrow::temporal_conversions::{
    MILLISECONDS, SECONDS_IN_DAY, timestamp_ms_to_datetime, timestamp_ns_to_datetime,
    timestamp_us_to_datetime,
};

use crate::month_start::roll_backward;
#[cfg(feature = "timezones")]
use crate::utils::{try_localize_datetime, unlocalize_datetime};
use crate::windows::duration::Duration;

// roll forward to the last day of the month
fn roll_forward(
    t: i64,
    time_zone: Option<&Tz>,
    timestamp_to_datetime: fn(i64) -> NaiveDateTime,
    datetime_to_timestamp: fn(NaiveDateTime) -> i64,
    offset_fn: fn(&Duration, i64, Option<&Tz>) -> PolarsResult<i64>,
) -> PolarsResult<i64> {
    // Use Ambiguous::Latest to roll back to the start of the month. It doesn't matter
    // if that timestamp lands on an ambiguous time as we then add 1 month anyway, we
    // could just as well use Ambiguous::Earliest.
    let naive_t = match time_zone {
        #[cfg(feature = "timezones")]
        Some(tz) => datetime_to_timestamp(unlocalize_datetime(timestamp_to_datetime(t), tz)),
        _ => t,
    };
    let naive_month_start_t =
        roll_backward(naive_t, None, timestamp_to_datetime, datetime_to_timestamp)?;
    let naive_result = offset_fn(
        &Duration::parse("-1d"),
        offset_fn(&Duration::parse("1mo"), naive_month_start_t, None)?,
        None,
    )?;
    let result = match time_zone {
        #[cfg(feature = "timezones")]
        Some(tz) => datetime_to_timestamp(
            try_localize_datetime(
                timestamp_to_datetime(naive_result),
                tz,
                Ambiguous::Raise,
                NonExistent::Raise,
            )?
            .expect("we didn't use Ambiguous::Null or NonExistent::Null"),
        ),
        _ => naive_result,
    };
    Ok(result)
}

pub trait PolarsMonthEnd {
    fn month_end(&self, time_zone: Option<&Tz>) -> PolarsResult<Self>
    where
        Self: Sized;
}

impl PolarsMonthEnd for DatetimeChunked {
    fn month_end(&self, time_zone: Option<&Tz>) -> PolarsResult<Self> {
        let timestamp_to_datetime: fn(i64) -> NaiveDateTime;
        let datetime_to_timestamp: fn(NaiveDateTime) -> i64;
        let offset_fn: fn(&Duration, i64, Option<&Tz>) -> PolarsResult<i64>;
        match self.time_unit() {
            TimeUnit::Nanoseconds => {
                timestamp_to_datetime = timestamp_ns_to_datetime;
                datetime_to_timestamp = datetime_to_timestamp_ns;
                offset_fn = Duration::add_ns;
            },
            TimeUnit::Microseconds => {
                timestamp_to_datetime = timestamp_us_to_datetime;
                datetime_to_timestamp = datetime_to_timestamp_us;
                offset_fn = Duration::add_us;
            },
            TimeUnit::Milliseconds => {
                timestamp_to_datetime = timestamp_ms_to_datetime;
                datetime_to_timestamp = datetime_to_timestamp_ms;
                offset_fn = Duration::add_ms;
            },
        };
        Ok(self
            .phys
            .try_apply_nonnull_values_generic(|t| {
                roll_forward(
                    t,
                    time_zone,
                    timestamp_to_datetime,
                    datetime_to_timestamp,
                    offset_fn,
                )
            })?
            .into_datetime(self.time_unit(), self.time_zone().clone()))
    }
}

impl PolarsMonthEnd for DateChunked {
    fn month_end(&self, _time_zone: Option<&Tz>) -> PolarsResult<Self> {
        const MSECS_IN_DAY: i64 = MILLISECONDS * SECONDS_IN_DAY;
        let ret = self.phys.try_apply_nonnull_values_generic(|t| {
            let fwd = roll_forward(
                MSECS_IN_DAY * t as i64,
                None,
                timestamp_ms_to_datetime,
                datetime_to_timestamp_ms,
                Duration::add_ms,
            )?;
            PolarsResult::Ok((fwd / MSECS_IN_DAY) as i32)
        })?;
        Ok(ret.into_date())
    }
}