//! Scheduling for events to run at certain intervals in the future

use chrono::{
    Date, DateTime, Datelike, Duration as CDuration, Local, NaiveDateTime, NaiveTime, TimeZone,
    Weekday,
};
use serde::{Deserialize, Serialize};
use std::cmp;
use std::iter::FromIterator;

/// A set of times of day (for [Schedule](struct.Schedule.html))
pub type TimeSet = Vec<NaiveTime>;
/// A set of days of week (for [Schedule](struct.Schedule.html))
pub type WeekdaySet = Vec<Weekday>;

/// Returns a [`WeekdaySet`](type.WeekdaySet.html) of every day of the week
#[allow(dead_code)]
pub fn every_day() -> WeekdaySet {
    WeekdaySet::from_iter(
        [
            Weekday::Mon,
            Weekday::Tue,
            Weekday::Wed,
            Weekday::Thu,
            Weekday::Fri,
            Weekday::Sat,
            Weekday::Sun,
        ]
        .iter()
        .cloned(),
    )
}

/// Represents the different types of date-time bounds that can be on a schedule
#[allow(dead_code)]
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DateTimeBound {
    /// There is no bound (ie. the Schedule extends with no limit)
    None,
    /// There is a bound that repeats every year (ie. the year is set to the current year)
    Yearly(NaiveDateTime),
    /// There is a definite bound on the schedule
    Definite(NaiveDateTime),
}

impl Default for DateTimeBound {
    fn default() -> DateTimeBound {
        DateTimeBound::None
    }
}

impl DateTimeBound {
    /// Resolves this bound into an optional `DateTime`. If there is no bound or the bound could
    /// not be resolved, None is returned.
    ///
    /// `reference` is the reference that is used to resolve a `Yearly` bound.
    pub fn resolve_from<Tz: TimeZone>(&self, reference: &DateTime<Tz>) -> Option<DateTime<Tz>> {
        match *self {
            DateTimeBound::None => None,
            DateTimeBound::Yearly(date_time) => {
                date_time.with_year(reference.year()).and_then(|date_time| {
                    reference
                        .timezone()
                        .from_local_datetime(&date_time)
                        .single()
                })
            }
            DateTimeBound::Definite(date_time) => reference
                .timezone()
                .from_local_datetime(&date_time)
                .single(),
        }
    }
}

/// A schedule that determines when an event will occur.
#[derive(Default, Debug, Clone, Serialize, Deserialize)]
pub struct Schedule {
    #[serde(
        serialize_with = "ser::serialize_times",
        deserialize_with = "ser::deserialize_times"
    )]
    pub times: TimeSet,
    #[serde(
        serialize_with = "ser::serialize_weekdays",
        deserialize_with = "ser::deserialize_weekdays"
    )]
    pub weekdays: WeekdaySet,
    pub from: DateTimeBound,
    pub to: DateTimeBound,
}

mod ser {
    use super::{DateTimeBound, TimeSet, WeekdaySet};
    use chrono::{NaiveDate, NaiveTime, Weekday};
    use serde::{Deserialize, Deserializer, Serialize, Serializer};
    use std::{convert::TryInto, fmt};

    #[derive(Default, Debug, Clone, Serialize, Deserialize)]
    struct TimeOfDay {
        hour: u32,
        minute: u32,
        second: u32,
        #[serde(default)]
        millisecond: u32,
    }

    impl From<&NaiveTime> for TimeOfDay {
        fn from(time: &NaiveTime) -> Self {
            use chrono::Timelike;
            Self {
                hour: time.hour(),
                minute: time.minute(),
                second: time.second(),
                millisecond: time.nanosecond() / 1_000_000_u32,
            }
        }
    }

    #[derive(Copy, Clone, Debug)]
    struct InvalidTimeOfDay;

    impl fmt::Display for InvalidTimeOfDay {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            "invalid time of day".fmt(f)
        }
    }

    impl TryInto<NaiveTime> for TimeOfDay {
        type Error = InvalidTimeOfDay;
        fn try_into(self) -> Result<NaiveTime, Self::Error> {
            NaiveTime::from_hms_milli_opt(self.hour, self.minute, self.second, self.millisecond)
                .ok_or(InvalidTimeOfDay)
        }
    }

    #[allow(clippy::ptr_arg)]
    pub fn serialize_times<S>(times: &TimeSet, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        serializer.collect_seq(times.iter().map(TimeOfDay::from))
    }

    pub fn deserialize_times<'de, D>(deserializer: D) -> Result<TimeSet, D::Error>
    where
        D: Deserializer<'de>,
    {
        use serde::de::{Error, SeqAccess, Visitor};

        struct TimeSetVisitor;

        impl<'de> Visitor<'de> for TimeSetVisitor {
            type Value = TimeSet;
            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("a sequence of time of days")
            }

            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
            where
                A: SeqAccess<'de>,
            {
                let mut times = TimeSet::with_capacity(seq.size_hint().unwrap_or(0));
                while let Some(value) = seq.next_element::<TimeOfDay>()? {
                    let time: NaiveTime = value.try_into().map_err(A::Error::custom)?;
                    times.push(time);
                }
                Ok(times)
            }
        }

        deserializer.deserialize_seq(TimeSetVisitor)
    }

    #[allow(clippy::ptr_arg)]
    pub fn serialize_weekdays<S>(weekdays: &WeekdaySet, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: Serializer,
    {
        let iter = weekdays
            .iter()
            .map(|weekday| weekday.num_days_from_sunday());
        serializer.collect_seq(iter)
    }

    #[derive(Copy, Clone, Debug)]
    struct InvalidWeekday;

    impl fmt::Display for InvalidWeekday {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            "weekday out of range 0 to 6".fmt(f)
        }
    }

    fn weekday_from_days_from_sunday(days: u32) -> Result<Weekday, InvalidWeekday> {
        Ok(match days {
            0 => Weekday::Sun,
            1 => Weekday::Mon,
            2 => Weekday::Tue,
            3 => Weekday::Wed,
            4 => Weekday::Thu,
            5 => Weekday::Fri,
            6 => Weekday::Sat,
            _ => return Err(InvalidWeekday),
        })
    }

    pub fn deserialize_weekdays<'de, D>(deserializer: D) -> Result<WeekdaySet, D::Error>
    where
        D: Deserializer<'de>,
    {
        use serde::de::{Error, SeqAccess, Visitor};

        struct WeekdaySetVisitor;

        impl<'de> Visitor<'de> for WeekdaySetVisitor {
            type Value = WeekdaySet;
            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
                formatter.write_str("a sequence of integers representing weekdays")
            }

            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
            where
                A: SeqAccess<'de>,
            {
                let mut weekdays = WeekdaySet::with_capacity(seq.size_hint().unwrap_or(0));
                while let Some(value) = seq.next_element::<u32>()? {
                    let weekday = weekday_from_days_from_sunday(value).map_err(A::Error::custom)?;
                    weekdays.push(weekday);
                }
                Ok(weekdays)
            }
        }

        deserializer.deserialize_seq(WeekdaySetVisitor)
    }

    #[derive(Clone, Debug, Serialize, Deserialize)]
    struct DateAndYear {
        year: i32,
        month: u32,
        day: u32,
    }

    impl From<NaiveDate> for DateAndYear {
        fn from(date: NaiveDate) -> Self {
            use chrono::Datelike;
            Self {
                year: date.year(),
                month: date.month(),
                day: date.day(),
            }
        }
    }

    #[derive(Copy, Clone, Debug)]
    struct InvalidDateAndYear;

    impl fmt::Display for InvalidDateAndYear {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            "invalid date or year".fmt(f)
        }
    }

    impl TryInto<NaiveDate> for DateAndYear {
        type Error = InvalidDateAndYear;
        fn try_into(self) -> Result<NaiveDate, Self::Error> {
            NaiveDate::from_ymd_opt(self.year, self.month, self.day).ok_or(InvalidDateAndYear)
        }
    }

    impl Serialize for DateTimeBound {
        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
        where
            S: Serializer,
        {
            match self {
                DateTimeBound::None => serializer.serialize_none(),
                DateTimeBound::Yearly(date_time) => {
                    // Discard time
                    let mut date_of_year: DateAndYear = date_time.date().into();
                    // Set year to 0 (since it is yearly)
                    date_of_year.year = 0;

                    date_of_year.serialize(serializer)
                }
                DateTimeBound::Definite(date_time) => {
                    // Discard time
                    let date_of_year: DateAndYear = date_time.date().into();

                    date_of_year.serialize(serializer)
                }
            }
        }
    }

    impl<'de> Deserialize<'de> for DateTimeBound {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: Deserializer<'de>,
        {
            use serde::de::Error;
            let date_of_year: Option<DateAndYear> = Deserialize::deserialize(deserializer)?;
            Ok(match date_of_year {
                Some(date_of_year) => {
                    let year = date_of_year.year;
                    let date: NaiveDate = date_of_year.try_into().map_err(D::Error::custom)?;
                    let date_time = date.and_hms(0, 0, 0);
                    if year == 0 {
                        DateTimeBound::Yearly(date_time)
                    } else {
                        DateTimeBound::Definite(date_time)
                    }
                }
                None => DateTimeBound::None,
            })
        }
    }
}

/// Gets the next date matching the `weekday` after `date`
fn next_weekday<Tz: TimeZone>(mut date: Date<Tz>, weekday: Weekday) -> Date<Tz> {
    while date.weekday() != weekday {
        date = date.succ();
    }
    date
}

#[allow(dead_code)]
impl Schedule {
    /// Creates a new Schedule.
    ///
    /// `times` is the times of day the event will be run. `weekdays` is the set of days of week
    /// the event will be run. `from` and `to` are restrictions on the end and beginning of event
    /// runs, respectively.
    pub fn new<T, W>(times: T, weekdays: W, from: DateTimeBound, to: DateTimeBound) -> Schedule
    where
        T: IntoIterator<Item = NaiveTime>,
        W: IntoIterator<Item = Weekday>,
    {
        Schedule {
            times: TimeSet::from_iter(times),
            weekdays: WeekdaySet::from_iter(weekdays),
            from,
            to,
        }
    }

    /// Gets the next `DateTime` the event should run after `reference`
    ///
    /// Returns `None` if the event will never run after `reference` (ie. must be a `from` bound)
    pub fn next_run_after<Tz: TimeZone>(&self, reference: &DateTime<Tz>) -> Option<DateTime<Tz>> {
        let mut to = self.to.resolve_from(reference);
        let mut from = self.from.resolve_from(reference);
        if let (Some(from), Some(to)) = (&mut from, &mut to) {
            // We must handle the case where yearly bounds cross a year boundary
            if to < from {
                if reference < to {
                    // Still in the bounds overlapping the previous year boundary
                    *from = from.with_year(from.year() - 1).unwrap();
                } else {
                    // Awaiting (or in) next years bounds
                    *to = to.with_year(to.year() + 1).unwrap();
                }
            }
        }
        let from = match (from, &to) {
            (Some(from), Some(to)) if &from > to => from.with_year(from.year() + 1),
            (from, _) => from,
        };
        let reference = match &from {
            Some(from) if from > reference => from,
            _ => reference,
        }
        .clone();
        let mut next_run: Option<DateTime<Tz>> = None;
        for weekday in &self.weekdays {
            for time in &self.times {
                let candidate = next_weekday(reference.date(), *weekday)
                    .and_time(*time)
                    .map(|date| {
                        if date < reference {
                            date + CDuration::weeks(1)
                        } else {
                            date
                        }
                    });
                let candidate = match (candidate, &to) {
                    (Some(date), Some(to)) if &date > to => None,
                    (date, _) => date,
                };
                next_run = match (next_run, candidate) {
                    // return whichever is first if there are 2 candidates
                    (Some(d1), Some(d2)) => Some(cmp::min(d1, d2)),
                    // otherwise return whichever isn't None (or None if both are)
                    (o1, o2) => o1.or(o2),
                }
            }
        }
        next_run
    }

    /// Gets the next run after the current (local) time
    ///
    /// See [next_run_after](#method.next_run_after)
    pub fn next_run_local(&self) -> Option<DateTime<Local>> {
        self.next_run_after(&Local::now())
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use chrono::NaiveDate;

    #[test]
    fn test_date_time_bound() {
        use super::DateTimeBound::*;

        let cases: Vec<(DateTimeBound, Option<DateTime<Local>>)> = vec![
            (None, Option::None),
            (
                Definite(NaiveDate::from_ymd(2016, 11, 16).and_hms(10, 30, 0)),
                Some(Local.ymd(2016, 11, 16).and_hms(10, 30, 0)),
            ),
            (
                Yearly(NaiveDate::from_ymd(2016, 11, 16).and_hms(10, 30, 0)),
                Some(Local.ymd(2018, 11, 16).and_hms(10, 30, 0)),
            ),
            (
                Yearly(NaiveDate::from_ymd(2016, 1, 1).and_hms(0, 0, 0)),
                Some(Local.ymd(2018, 1, 1).and_hms(0, 0, 0)),
            ),
            (
                Yearly(NaiveDate::from_ymd(2016, 12, 31).and_hms(23, 59, 59)),
                Some(Local.ymd(2018, 12, 31).and_hms(23, 59, 59)),
            ),
            (
                Yearly(NaiveDate::from_ymd(2012, 2, 29).and_hms(0, 0, 0)),
                Option::None,
            ), /* leap day */
        ];
        let from = Local.ymd(2018, 1, 1).and_hms(0, 0, 0);

        for (bound, expected_result) in cases {
            let result = bound.resolve_from(&from);
            assert_eq!(result, expected_result);
        }
    }

    #[test]
    fn test_next_weekday() {
        use super::next_weekday;
        use chrono::Weekday;
        // (date, weekday, result)
        let cases: Vec<(Date<Local>, Weekday, Date<Local>)> = vec![
            (
                Local.ymd(2016, 11, 16),
                Weekday::Wed,
                Local.ymd(2016, 11, 16),
            ),
            (
                Local.ymd(2016, 11, 16),
                Weekday::Fri,
                Local.ymd(2016, 11, 18),
            ),
            (
                Local.ymd(2016, 11, 16),
                Weekday::Tue,
                Local.ymd(2016, 11, 22),
            ),
            (Local.ymd(2016, 12, 30), Weekday::Tue, Local.ymd(2017, 1, 3)),
            (
                Local.ymd(2016, 11, 16),
                Weekday::Tue,
                Local.ymd(2016, 11, 22),
            ),
        ];

        for (date, weekday, expected_result) in cases {
            let result = next_weekday(date, weekday);
            assert_eq!(result, expected_result);
        }
    }

    #[test]
    fn test_next_run_after() {
        use super::{DateTimeBound, Schedule};
        use chrono::{DateTime, Local, NaiveTime, TimeZone, Weekday};
        let schedule = Schedule::new(
            vec![NaiveTime::from_hms(10, 30, 0)],
            vec![Weekday::Wed],
            DateTimeBound::None,
            DateTimeBound::None,
        );
        let cases: Vec<(DateTime<Local>, Option<DateTime<Local>>)> = vec![
            (
                Local.ymd(2016, 11, 14).and_hms(10, 30, 0),
                Some(Local.ymd(2016, 11, 16).and_hms(10, 30, 0)),
            ),
            (
                Local.ymd(2016, 11, 16).and_hms(10, 20, 0),
                Some(Local.ymd(2016, 11, 16).and_hms(10, 30, 0)),
            ),
            (
                Local.ymd(2016, 11, 16).and_hms(10, 40, 0),
                Some(Local.ymd(2016, 11, 23).and_hms(10, 30, 0)),
            ),
        ];
        for (reference, expected_result) in cases {
            let result = schedule.next_run_after(&reference);
            assert_eq!(result, expected_result);
        }
    }

    #[test]
    fn test_next_run_after2() {
        use super::{DateTimeBound, Schedule};
        use chrono::{DateTime, Local, NaiveTime, TimeZone, Weekday};
        #[derive(Debug)]
        struct Case {
            schedule: Schedule,
            ref_time: DateTime<Local>,
            expected_result: Option<DateTime<Local>>,
        }
        impl Case {
            fn new(
                schedule: Schedule,
                ref_time: DateTime<Local>,
                expected_result: Option<DateTime<Local>>,
            ) -> Self {
                Self {
                    schedule,
                    ref_time,
                    expected_result,
                }
            }
        }
        let sched1 = Schedule::new(
            vec![NaiveTime::from_hms(8, 30, 0), NaiveTime::from_hms(20, 0, 0)],
            vec![Weekday::Thu, Weekday::Fri],
            DateTimeBound::None,
            DateTimeBound::None,
        );
        let sched2 = Schedule::new(
            vec![NaiveTime::from_hms(8, 30, 0), NaiveTime::from_hms(20, 0, 0)],
            vec![Weekday::Thu, Weekday::Fri],
            DateTimeBound::Definite(NaiveDate::from_ymd(2016, 5, 30).and_hms(0, 0, 0)),
            DateTimeBound::Definite(NaiveDate::from_ymd(2016, 6, 30).and_hms(0, 0, 0)),
        );
        let sched3 = Schedule::new(
            vec![NaiveTime::from_hms(8, 30, 0), NaiveTime::from_hms(20, 0, 0)],
            every_day(),
            DateTimeBound::Yearly(NaiveDate::from_ymd(0, 12, 15).and_hms(0, 0, 0)),
            DateTimeBound::Yearly(NaiveDate::from_ymd(0, 1, 15).and_hms(0, 0, 0)),
        );
        let cases: Vec<Case> = vec![
            Case::new(
                sched1.clone(),
                Local.ymd(2016, 5, 16).and_hms(0, 0, 0),
                Some(Local.ymd(2016, 5, 19).and_hms(8, 30, 0)),
            ),
            Case::new(
                sched1,
                Local.ymd(2016, 5, 20).and_hms(9, 0, 0),
                Some(Local.ymd(2016, 5, 20).and_hms(20, 0, 0)),
            ),
            Case::new(
                sched2.clone(),
                Local.ymd(2016, 6, 1).and_hms(0, 0, 0),
                Some(Local.ymd(2016, 6, 2).and_hms(8, 30, 0)),
            ),
            Case::new(
                sched2.clone(),
                Local.ymd(2016, 5, 1).and_hms(0, 0, 0),
                Some(Local.ymd(2016, 6, 2).and_hms(8, 30, 0)),
            ),
            Case::new(sched2, Local.ymd(2016, 7, 1).and_hms(0, 0, 0), None),
            Case::new(
                sched3.clone(),
                Local.ymd(2016, 11, 1).and_hms(0, 0, 0),
                Some(Local.ymd(2016, 12, 15).and_hms(8, 30, 0)),
            ),
            Case::new(
                sched3.clone(),
                Local.ymd(2017, 1, 1).and_hms(9, 0, 0),
                Some(Local.ymd(2017, 1, 1).and_hms(20, 0, 0)),
            ),
            Case::new(
                sched3,
                Local.ymd(2016, 1, 30).and_hms(0, 0, 0),
                Some(Local.ymd(2016, 12, 15).and_hms(8, 30, 0)),
            ),
        ];
        for case in cases {
            let result = case.schedule.next_run_after(&case.ref_time);
            assert_eq!(result, case.expected_result, "case failed: {:?}", case);
        }
    }

    #[test]
    fn test_serialize() {
        let sched = Schedule::new(
            vec![
                NaiveTime::from_hms_milli(0, 0, 0, 0),
                NaiveTime::from_hms_milli(23, 59, 59, 999),
            ],
            every_day(),
            DateTimeBound::Yearly(NaiveDate::from_ymd(2020, 1, 1).and_hms(0, 0, 0)),
            DateTimeBound::Definite(NaiveDate::from_ymd(9999, 12, 31).and_hms(23, 59, 59)),
        );
        let ser = serde_json::to_string(&sched).unwrap();
        // Weekdays should match the order in `every_day()` but with sunday being 0
        assert_eq!(
            &ser,
            "{\
            \"times\":[\
                {\"hour\":0,\"minute\":0,\"second\":0,\"millisecond\":0},\
                {\"hour\":23,\"minute\":59,\"second\":59,\"millisecond\":999}\
            ],\
            \"weekdays\":[1,2,3,4,5,6,0],\
            \"from\":{\
                \"year\":0,\"month\":1,\"day\":1\
            },\
            \"to\":{\
                \"year\":9999,\"month\":12,\"day\":31\
            }\
        }"
        );
        let sched_de: Schedule = serde_json::from_str(&ser).unwrap();
        assert_eq!(sched.times, sched_de.times);
        assert_eq!(sched.weekdays, sched_de.weekdays);
        // This serialization is lossy (year is discarded for yearly)
        // assert_eq!(sched_de.from, sched.from);
        assert_eq!(
            sched_de.from,
            DateTimeBound::Yearly(NaiveDate::from_ymd(0, 1, 1).and_hms(0, 0, 0))
        );
        // This serialization is also lossy (time is discarded)
        // assert_eq!(sched_de.to, sched.to);
        assert_eq!(
            sched_de.to,
            DateTimeBound::Definite(NaiveDate::from_ymd(9999, 12, 31).and_hms(0, 0, 0))
        );
    }
}