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use chrono::{DateTime, Datelike, NaiveDate, TimeZone, Timelike};

use crate::Expr;

pub struct CronEvaluator<'a, Tz: TimeZone> {
  instant: &'a DateTime<Tz>,
}

pub struct Environment {
  now: u8,
  max: u8,
}

impl Environment {
  pub fn new(now: u8, max: u8) -> Self {
    Self { now, max }
  }
}

fn get_days_from_month(year: i32, month: u32) -> Option<i64> {
  NaiveDate::from_ymd_opt(
    match month {
      12 => year + 1,
      _ => year,
    },
    match month {
      12 => 1,
      _ => month + 1,
    },
    1,
  )
  .map(|d| {
    d.signed_duration_since(NaiveDate::from_ymd_opt(year, month, 1).unwrap())
      .num_days()
  })
}

impl<'a, Tz: TimeZone> CronEvaluator<'a, Tz> {
  pub fn new(instant: &'a DateTime<Tz>) -> Self {
    Self { instant }
  }

  pub fn eval(&self, ast: &Expr) -> bool {
    match ast {
      Expr::CronExpr {
        box mins,
        box hours,
        box months,
        box days,
        box day_of_weeks,
      } => {
        let last_day =
          get_days_from_month(self.instant.date_naive().year(), self.instant.date_naive().month()).unwrap();
        let fmins = self.visit0(&Environment::new(self.instant.time().minute() as u8, 59), mins);
        let fhours = self.visit0(&Environment::new(self.instant.time().hour() as u8, 23), hours);
        let fdays = self.visit0(
          &Environment::new(self.instant.date_naive().day() as u8, last_day as u8),
          days,
        );
        let fmonths = self.visit0(&Environment::new(self.instant.date_naive().month() as u8, 12), months);
        let fday_of_weeks = self.visit0(&Environment::new(self.instant.time().minute() as u8, 7), day_of_weeks);
        fmins && fhours && fdays && fmonths && fday_of_weeks
      }
      _ => false,
    }
  }

  fn visit1(&self, env: &Environment, ast: &Expr) -> bool {
    match ast {
      Expr::AnyValueExpr => true,
      Expr::LastValueExpr if env.now == env.max => true,
      Expr::ValueExpr(n) if env.now == *n => true,
      Expr::ListExpr(list) => list.iter().any(|e| self.visit0(env, e)),
      Expr::RangeExpr {
        from: box Expr::ValueExpr(start),
        to: box Expr::ValueExpr(end),
        per_option,
      } => match per_option {
        box Expr::NoOp if *start <= env.now && env.now <= *end => true,
        box Expr::ValueExpr(per) => (*start as usize..=*end as usize)
          .step_by(*per as usize)
          .into_iter()
          .any(|e| e == env.now as usize),
        _ => false,
      },
      Expr::PerExpr {
        digit: box Expr::AnyValueExpr,
        option: box Expr::ValueExpr(per),
      } => (0usize..=(env.max as usize))
        .step_by(*per as usize)
        .into_iter()
        .any(|e| e == env.now as usize),
      _ => false,
    }
  }

  fn visit0(&self, env: &Environment, ast: &Expr) -> bool {
    self.visit1(env, ast)
  }
}

#[cfg(test)]
mod tests {
  use chrono::{TimeZone, Utc};

  use crate::cron_evaluator::CronEvaluator;
  use crate::Expr;

  #[test]
  fn test_anytime() {
    let date_time = Utc.with_ymd_and_hms(2021, 1, 1, 1, 1, 1).unwrap();
    let cron_evaluator = CronEvaluator::new(&date_time);
    let expr = Expr::CronExpr {
      mins: Box::from(Expr::AnyValueExpr),
      hours: Box::from(Expr::AnyValueExpr),
      days: Box::from(Expr::AnyValueExpr),
      months: Box::from(Expr::AnyValueExpr),
      day_of_weeks: Box::from(Expr::AnyValueExpr),
    };
    let result = cron_evaluator.eval(&expr);
    assert!(result)
  }

  #[test]
  fn test_point_time() {
    let date_time = Utc.with_ymd_and_hms(2021, 1, 1, 1, 1, 1).unwrap();
    let cron_evaluator = CronEvaluator::new(&date_time);
    let expr = Expr::CronExpr {
      mins: Box::from(Expr::ValueExpr(1)),
      hours: Box::from(Expr::ValueExpr(1)),
      days: Box::from(Expr::ValueExpr(1)),
      months: Box::from(Expr::ValueExpr(1)),
      day_of_weeks: Box::from(Expr::AnyValueExpr),
    };
    let result = cron_evaluator.eval(&expr);
    assert!(result)
  }
}