crontab 0.2.0

A lightweight crontab parser.
Documentation 
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use time::Tm;

/// Advance the year, but leave all other fields untouched.
/// This can result in an invalid day-of-month, day-of-year, or day-of-week!
pub (crate) fn adv_year(time: &mut Tm) {
  time.tm_year += 1;
}

/// Advance the day, but leave the day (and hour, minute, second) untouched.
/// This can result in an invalid day-of-month!
pub (crate) fn adv_month(time: &mut Tm) {
  time.tm_mon += 1;
  if time.tm_mon > 11 {
    time.tm_mon = 0;
    adv_year(time);
  }
}

/// Advance the day, but leave the hour, minute, and second untouched.
pub (crate) fn adv_day(time: &mut Tm) {
  time.tm_wday = (time.tm_wday + 1) % 7; // day of week
  time.tm_mday += 1; // day of month

  let is_leap_year = {
    let year = time.tm_year + 1900;
    if year % 400 == 0
        || (year % 4 == 0 && year % 100 != 0) {
      true
    } else {
      false
    }
  };

  let days_in_year = if is_leap_year { 366 } else { 365 };

  time.tm_yday = (time.tm_yday + 1) % days_in_year; // day of year

  match time.tm_mon {
    0 | 2 | 4 | 6 | 7 | 9 | 11 => {
      if time.tm_mday > 31 {
        time.tm_mday = 1;
        adv_month(time);
      }
    },
    3 | 5 | 8 | 10 => {
      if time.tm_mday > 30 {
        time.tm_mday = 1;
        adv_month(time);
      }
    },
    1 => {
      let mdays = if is_leap_year { 29 } else { 28 };

      if time.tm_mday > mdays {
        time.tm_mday = 1;
        adv_month(time);
      }
    },
    _ => {}, // bad user input
  }
}

/// Advance the hour, but leave the minute and second untouched.
pub (crate) fn adv_hour(time: &mut Tm) {
  time.tm_hour += 1;
  if time.tm_hour > 23 {
    time.tm_hour = 0;
    adv_day(time);
  }
}

/// Advance the minute, but leave the second untouched.
pub (crate) fn adv_minute(time: &mut Tm) {
  time.tm_min += 1;
  if time.tm_min > 59 {
    time.tm_min = 0;
    adv_hour(time);
  }
}

#[cfg(test)]
mod tests {
  use super::*;
  use expectest::prelude::*;
  use test_helpers::get_tm;
  use test_helpers::normal;
  use time::{Timespec, at_utc};

  #[test]
  pub fn test_adv_year() {
    let mut tm = get_tm(2017, 10, 6, 12, 24, 0);
    adv_year(&mut tm);
    expect!(normal(&tm)).to(be_equal_to(get_tm(2018, 10, 6, 12, 24, 0)));
  }

  #[test]
  pub fn test_adv_month() {
    // January
    let mut tm = get_tm(2017, 1, 1, 12, 0, 0);
    adv_month(&mut tm);
    expect!(normal(&tm)).to(be_equal_to(get_tm(2017, 2, 1, 12, 0, 0)));

    // December
    let mut tm = get_tm(2017, 12, 1, 0, 0, 0);
    adv_month(&mut tm);
    expect!(normal(&tm)).to(be_equal_to(get_tm(2018, 1, 1, 0, 0, 0)));
  }

  #[test]
  pub fn test_adv_day_on_mday() {
    // 2017-01-01 00:00 UTC, a non-leap year starting on a Sunday (tm_wday=0).
    let timespec = Timespec::new(1483228800, 0);
    let mut tm = at_utc(timespec);

    // 2017 to 2019 are not leap years
    let days_in_months = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

    // 2017 is (tm_year=117)
    for tm_year in 117 .. 120 {
      expect!(tm.tm_year).to(be_equal_to(tm_year));

      for days_in_month in days_in_months.iter() {
        let bound = days_in_month + 1; // 1-indexed
        for expected_day in 1..bound {
          expect!(tm.tm_mday).to(be_equal_to(expected_day));
          adv_day(&mut tm);
        }
      }
    }

    expect!(tm.tm_year).to(be_equal_to(120));

    // 2020 is a leap-year
    let days_in_months = [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

    for days_in_month in days_in_months.iter() {
      let bound = days_in_month + 1; // 1-indexed
      for expected_day in 1..bound {
        expect!(tm.tm_mday).to(be_equal_to(expected_day));
        adv_day(&mut tm);
      }
    }

    expect!(tm.tm_year).to(be_equal_to(121));
  }

  #[test]
  pub fn test_adv_day_on_wday() {
    // 2017-01-01 00:00 UTC, a non-leap year starting on a Sunday (tm_wday=0).
    let timespec = Timespec::new(1483228800, 0);
    let mut tm = at_utc(timespec);

    // First week.
    expect!(tm.tm_wday).to(be_equal_to(0));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(1));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(2));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(3));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(4));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(5));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(6));
    adv_day(&mut tm);
    expect!(tm.tm_wday).to(be_equal_to(0)); // Back to sunday!

    // Four more years...
    let mut expected = 0;
    for _ in 0 .. 1460 {
      expected = (expected + 1) % 7;
      adv_day(&mut tm);
      expect!(tm.tm_wday).to(be_equal_to(expected));
    }

    // Reset.
    let mut tm = at_utc(timespec);

    expect!(tm.tm_year).to(be_equal_to(117)); // 2017
    expect!(tm.tm_wday).to(be_equal_to(0)); // Starts on a Sunday

    // Entire year.
    for _ in 0 .. 365 {
      adv_day(&mut tm);
    }

    // Now it's 2018-01-01
    expect!(tm.tm_year).to(be_equal_to(118)); // 2018
    expect!(tm.tm_wday).to(be_equal_to(1)); // Starts on a Monday
  }

  #[test]
  pub fn test_adv_day_on_yday() {
    // 2017-01-01 00:00 UTC, a non-leap year starting on a Sunday (tm_wday=0).
    let timespec = Timespec::new(1483228800, 0);
    let mut tm = at_utc(timespec);

    // First day of 2017. (tm_year=117)
    expect!(tm.tm_year).to(be_equal_to(117));
    expect!(tm.tm_yday).to(be_equal_to(0));

    // 2017 passes...
    for expected_day in 0 .. 365 {
      expect!(tm.tm_year).to(be_equal_to(117)); // 2017
      expect!(tm.tm_yday).to(be_equal_to(expected_day));
      adv_day(&mut tm);
    }

    // First day of 2018.
    expect!(tm.tm_year).to(be_equal_to(118));
    expect!(tm.tm_yday).to(be_equal_to(0));

    // 2018 and 2019 pass... (Also not leap years.)
    for year in 118 .. 120 {
      for expected_day in 0 .. 365 {
        expect!(tm.tm_year).to(be_equal_to(year));
        expect!(tm.tm_yday).to(be_equal_to(expected_day));
        adv_day(&mut tm);
      }
    }

    // First day of 2020.
    expect!(tm.tm_year).to(be_equal_to(120));
    expect!(tm.tm_yday).to(be_equal_to(0));

    // This is a leap year!
    for expected_day in 0 .. 366 {
      expect!(tm.tm_year).to(be_equal_to(120));
      expect!(tm.tm_yday).to(be_equal_to(expected_day));
      adv_day(&mut tm);
    }

    // First day of 2021.
    expect!(tm.tm_year).to(be_equal_to(121));
    expect!(tm.tm_yday).to(be_equal_to(0));
  }
}