use chrono::{
    DateTime, Utc, Local, TimeZone, LocalResult, FixedOffset, Datelike,
};
use regex::Regex;

use crate::error::{Result, Error};

fn date_from_parts<T: TimeZone>(
    timezone: T, input: &str, year: i32, month: u32, day: u32, hour: u32,
    minute: u32, second: u32
) -> Result<DateTime<Utc>> {
    let try_date = timezone.ymd_opt(
        year, month, day
        ).and_hms_opt(
            hour, minute, second
            );

    match try_date {
        LocalResult::None => Err(Error::NoneLocalTime(input.into())),
        LocalResult::Single(t) => Ok(Utc.from_utc_datetime(&t.naive_utc())),
        LocalResult::Ambiguous(t1, t2) => Err(Error::AmbiguousLocalTime {
            orig: input.into(),
            t1: t1.naive_utc(),
            t2: t2.naive_utc(),
        }),
    }
}

fn offset_from_parts(east: bool, hours: i32, minutes: i32) -> FixedOffset {
    let mut second: i32 = hours * 60 * 60;
    second += minutes * 60;

    if east {
        FixedOffset::east(second)
    } else {
        FixedOffset::west(second)
    }
}

#[inline]
fn date_parts<T: Datelike>(t: T) -> (i32, u32, u32) {
    (t.year(), t.month(), t.day())
}

pub fn parse_time(input: &str) -> Result<DateTime<Utc>> {
    // first try to parse as a full datetime with optional timezone
    let datetime_re = Regex::new(r"(?xi)
        (?P<year>\d{4})  # the year, mandatory
        .
        (?P<month>\d{2}) # the month, mandatory
        .
        (?P<day>\d{2})   # the day, mandatory
        (. # a separator
        (?P<hour>\d{2}) # the hour, optional
        (. # a separator
        (?P<minute>\d{2})? # the minute, optional
        (. # a separator
        (?P<second>\d{2}))?)?)? # the second, optional, implies minute
        (?P<offset>
            (?P<utc>Z)|((?P<sign>\+|-)(?P<ohour>\d{1,2}):(?P<omin>\d{2}))
        )? # the offset, optional
    ").unwrap();

    if let Some(caps) = datetime_re.captures(input) {
        let year: i32 = (&caps["year"]).parse().unwrap();
        let month: u32 = (&caps["month"]).parse().unwrap();
        let day: u32 = (&caps["day"]).parse().unwrap();
        let hour: u32 = caps.name("hour").map(|t| t.as_str().parse().unwrap()).unwrap_or(0);
        let minute: u32 = caps.name("minute").map(|t| t.as_str().parse().unwrap()).unwrap_or(0);
        let second: u32 = caps.name("second").map(|t| t.as_str().parse().unwrap()).unwrap_or(0);

        return if let Some(_) = caps.name("offset") {
            if let Some(_) = caps.name("utc") {
                date_from_parts(
                    Utc, input, year, month, day, hour, minute, second,
                )
            } else {
                let hours: i32 = (&caps["ohour"]).parse().unwrap();
                let minutes: i32 = (&caps["omin"]).parse().unwrap();
                let fo = offset_from_parts(&caps["sign"] == "+", hours, minutes);

                date_from_parts(
                    fo, input, year, month, day, hour, minute, second,
                )
            }
        } else {
            // start with a local time
            date_from_parts(
                Local, input, year, month, day, hour, minute, second,
            )
        };
    }

    let hour_re = Regex::new(r"(?xi)
        (?P<hour>\d{1,2}) # the hour, mandatory
        (. # a separator
        (?P<minute>\d{2})? # the minute, optional
        (. # a separator
        (?P<second>\d{2}))?)? # the second, optional, implies minute
        (?P<offset>
            (?P<utc>Z)|((?P<sign>\+|-)(?P<ohour>\d{1,2}):(?P<omin>\d{2}))
        )? # the offset, optional
    ").unwrap();

    if let Some(caps) = hour_re.captures(input) {
        let hour: u32 = (&caps["hour"]).parse().unwrap();
        let minute: u32 = caps.name("minute").map(|t| t.as_str().parse().unwrap()).unwrap_or(0);
        let second: u32 = caps.name("second").map(|t| t.as_str().parse().unwrap()).unwrap_or(0);

        return if let Some(_) = caps.name("offset") {
            if let Some(_) = caps.name("utc") {
                let (year, month, day) = date_parts(Utc::now());

                date_from_parts(
                    Utc, input, year, month, day, hour, minute, second,
                )
            } else {
                let hours: i32 = (&caps["ohour"]).parse().unwrap();
                let minutes: i32 = (&caps["omin"]).parse().unwrap();
                let fo = offset_from_parts(&caps["sign"] == "+", hours, minutes);
                let (year, month, day) = date_parts(fo.from_utc_datetime(&Utc::now().naive_utc()));

                date_from_parts(
                    fo, input, year, month, day, hour, minute, second,
                )
            }
        } else {
            let (year, month, day) = date_parts(Local::now());

            date_from_parts(
                Local, input, year, month, day, hour, minute, second,
            )
        };
    }

    Err(Error::DateTimeParseError(input.into()))
}

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

    use super::*;

    const HOURS: i32 = 3600;

    #[test]
    fn parse_datetime_string() {
        assert_eq!(parse_time("2021-05-21 11:36").unwrap(), Local.ymd(2021, 5, 21).and_hms(11, 36, 0));
        assert_eq!(parse_time("2021-05-21 11:36:12").unwrap(), Local.ymd(2021, 5, 21).and_hms(11, 36, 12));

        assert_eq!(parse_time("2021-05-21T11:36").unwrap(), Local.ymd(2021, 5, 21).and_hms(11, 36, 0));
        assert_eq!(parse_time("2021-05-21T11:36:12").unwrap(), Local.ymd(2021, 5, 21).and_hms(11, 36, 12));
    }

    #[test]
    fn parse_date() {
        assert_eq!(parse_time("2021-05-21").unwrap(), Local.ymd(2021, 5, 21).and_hms(0, 0, 0));
    }

    #[test]
    fn parse_hour() {
        let localdate = Local::now().date();

        assert_eq!(parse_time("11:36").unwrap(), localdate.and_hms(11, 36, 0));
        assert_eq!(parse_time("11:36:35").unwrap(), localdate.and_hms(11, 36, 35));
    }

    #[test]
    fn parse_hour_with_timezone() {
        let todayutc = Utc::now().date();

        assert_eq!(parse_time("11:36Z").unwrap(), todayutc.and_hms(11, 36, 0));
        assert_eq!(parse_time("11:36:35z").unwrap(), todayutc.and_hms(11, 36, 35));

        let offset = FixedOffset::west(5 * HOURS);
        let todayoffset = offset.from_utc_datetime(&Utc::now().naive_utc()).date();
        assert_eq!(parse_time("11:36-5:00").unwrap(), todayoffset.and_hms(11, 36, 0));

        let offset = FixedOffset::east(5 * HOURS);
        let todayoffset = offset.from_utc_datetime(&Utc::now().naive_utc()).date();
        assert_eq!(parse_time("11:36:35+5:00").unwrap(), todayoffset.and_hms(11, 36, 35));
    }

    #[test]
    fn parse_with_specified_timezone() {
        assert_eq!(parse_time("2021-05-21T11:36:12Z").unwrap(), Utc.ymd(2021, 5, 21).and_hms(11, 36, 12));
        assert_eq!(parse_time("2021-05-21T11:36:12-3:00").unwrap(), Utc.ymd(2021, 5, 21).and_hms(14, 36, 12));
        assert_eq!(parse_time("2021-05-21T11:36:12+3:00").unwrap(), Utc.ymd(2021, 5, 21).and_hms(8, 36, 12));
    }

    #[test]
    fn parse_human_time() {
        assert_eq!(parse_time("an hour ago").unwrap(), Local::now() - Duration::hours(1));
        assert_eq!(parse_time("one hour ago").unwrap(), Local::now() - Duration::hours(1));
        assert_eq!(parse_time("two hours ago").unwrap(), Local::now() - Duration::hours(2));
        assert_eq!(parse_time("three hours ago").unwrap(), Local::now() - Duration::hours(2));

        assert_eq!(parse_time("4 hours ago").unwrap(), Local::now().date().and_hms(11, 36, 12));

        assert_eq!(parse_time("a minute ago").unwrap(), Local::now().date().and_hms(11, 36, 12));
        assert_eq!(parse_time("two minutes ago").unwrap(), Local::now().date().and_hms(11, 36, 12));
        assert_eq!(parse_time("4 minutes ago").unwrap(), Local::now().date().and_hms(11, 36, 12));
    }
}