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

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

mod strings;

use strings::{NUMBER_VALUES, HUMAN_REGEX, DATETIME_REGEX, HOUR_REGEX};

#[allow(clippy::too_many_arguments)]
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.with_ymd_and_hms(
        year, month, day, hour, minute, second
    );

    match try_date {
        LocalResult::None => Err(Error::NoneLocalTime(input.into())),
        LocalResult::Single(t) => Ok(t.with_timezone(&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_opt(second).unwrap()
    } else {
        FixedOffset::west_opt(second).unwrap()
    }
}

#[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>> {
    if let Some(caps) = HUMAN_REGEX.captures(input) {
        let hours = if caps.name("hour").is_some() {
            if let Some(m) = caps.name("hcase") {
                NUMBER_VALUES[m.as_str()]
            } else if let Some(m) = caps.name("hdigit") {
                NUMBER_VALUES[m.as_str()]
            } else if let Some(m) = caps.name("hten") {
                NUMBER_VALUES[m.as_str()]
            } else if caps.name("hcomposed").is_some() {
                NUMBER_VALUES[&caps["hcten"]] + NUMBER_VALUES[&caps["hcdigit"]]
            } else if let Some(m) = caps.name("htextualnum") {
                m.as_str().parse().unwrap()
            } else if caps.name("half").is_some() {
                0.5
            } else {
                unreachable!()
            }
        } else {
            0.
        };

        let minutes = if caps.name("minute").is_some() {
            if let Some(m) = caps.name("mcase") {
                NUMBER_VALUES[m.as_str()]
            } else if let Some(m) = caps.name("mdigit") {
                NUMBER_VALUES[m.as_str()]
            } else if let Some(m) = caps.name("mten") {
                NUMBER_VALUES[m.as_str()]
            } else if caps.name("mcomposed").is_some() {
                NUMBER_VALUES[&caps["mcten"]] + NUMBER_VALUES[&caps["mcdigit"]]
            } else if let Some(m) = caps.name("mtextualnum") {
                m.as_str().parse().unwrap()
            } else {
                unreachable!()
            }
        } else {
            0.
        };

        return Ok(Utc.from_utc_datetime(
            &(Local::now() - Duration::minutes((hours * 60. + minutes) as i64)).naive_utc()
        ));
    }

    // first try to parse as a full datetime with optional timezone
    if let Some(caps) = DATETIME_REGEX.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 caps.name("offset").is_some() {
            if caps.name("utc").is_some() {
                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,
            )
        };
    }

    if let Some(caps) = HOUR_REGEX.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 caps.name("offset").is_some() {
            if caps.name("utc").is_some() {
                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()))
}

pub fn parse_hours(input: &str) -> Result<u16> {
    input.parse().map_err(|_| Error::InvalidHours(input.to_string()))
}

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

    use super::*;

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

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

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

    #[test]
    fn parse_hour() {
        let localdate = Local::now().with_hour(0).unwrap().with_minute(0).unwrap().with_second(0).unwrap().with_nanosecond(0).unwrap();

        assert_eq!(parse_time("11:36").unwrap(), localdate.with_hour(11).unwrap().with_minute(36).unwrap().with_timezone(&Utc));
        assert_eq!(parse_time("11:36:35").unwrap(), localdate.with_hour(11).unwrap().with_minute(36).unwrap().with_second(35).unwrap().with_timezone(&Utc));
    }

    #[test]
    fn parse_hour_with_timezone() {
        let hours: i32 = 3600;
        let todayutc = Utc::now().date_naive();

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

        let offset = FixedOffset::west_opt(5 * hours).unwrap();
        let today_at_offset = offset.from_utc_datetime(&Utc::now().naive_utc()).with_hour(0).unwrap().with_minute(0).unwrap().with_second(0).unwrap().with_nanosecond(0).unwrap();
        assert_eq!(parse_time("11:36-5:00").unwrap(), today_at_offset.with_hour(11).unwrap().with_minute(36).unwrap().with_timezone(&Utc));

        let offset = FixedOffset::east_opt(5 * hours).unwrap();
        let today_at_offset = offset.from_utc_datetime(&Utc::now().naive_utc()).with_hour(0).unwrap().with_minute(0).unwrap().with_second(0).unwrap().with_nanosecond(0).unwrap();
        assert_eq!(parse_time("11:36:35+5:00").unwrap(), today_at_offset.with_hour(11).unwrap().with_minute(36).unwrap().with_second(35).unwrap().with_timezone(&Utc));
    }

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

    fn time_diff(t1: DateTime<Utc>, t2: DateTime<Local>) {
        let diff = dbg!(dbg!(t1) - dbg!(Utc.from_utc_datetime(&t2.naive_utc()))).num_seconds().abs();

        assert!(diff < 1, "too different: {} s", diff);
    }

    #[test]
    fn parse_human_times() {
        // hours
        time_diff(parse_time("an hour ago").unwrap(), Local::now() - Duration::hours(1));
        time_diff(parse_time("two hours ago").unwrap(), Local::now() - Duration::hours(2));
        time_diff(parse_time("ten hours ago").unwrap(), Local::now() - Duration::hours(10));
        time_diff(parse_time("twenty one hours ago").unwrap(), Local::now() - Duration::hours(21));
        time_diff(parse_time("15 hours ago").unwrap(), Local::now() - Duration::hours(15));

        // minutes
        time_diff(parse_time("a minute ago").unwrap(), Local::now() - Duration::minutes(1));
        time_diff(parse_time("two minutes ago").unwrap(), Local::now() - Duration::minutes(2));
        time_diff(parse_time("thirty minutes ago").unwrap(), Local::now() - Duration::minutes(30));
        time_diff(parse_time("forty one minutes ago").unwrap(), Local::now() - Duration::minutes(41));
        time_diff(parse_time("1 minute ago").unwrap(), Local::now() - Duration::minutes(1));
        time_diff(parse_time("23 minutes ago").unwrap(), Local::now() - Duration::minutes(23));
        time_diff(parse_time("half an hour ago").unwrap(), Local::now() - Duration::minutes(30));

        // mixed
        time_diff(parse_time("an hour 10 minutes ago").unwrap(), Local::now() - Duration::minutes(70));
        time_diff(parse_time("2 hours five minutes ago").unwrap(), Local::now() - Duration::minutes(125));
        time_diff(parse_time("an hour 12 minutes ago").unwrap(), Local::now() - Duration::minutes(60 + 12));

        // abbreviated
        time_diff(parse_time("2hrs ago").unwrap(), Local::now() - Duration::hours(2));
        time_diff(parse_time("10min ago").unwrap(), Local::now() - Duration::minutes(10));
        time_diff(parse_time("1hr ago").unwrap(), Local::now() - Duration::hours(1));
        time_diff(parse_time("1h ago").unwrap(), Local::now() - Duration::hours(1));
        time_diff(parse_time("1h 5m ago").unwrap(), Local::now() - Duration::minutes(60 + 5));
        time_diff(parse_time("1h5m ago").unwrap(), Local::now() - Duration::minutes(60 + 5));
        time_diff(parse_time("a m ago").unwrap(), Local::now() - Duration::minutes(1));
        time_diff(parse_time("an hr ago").unwrap(), Local::now() - Duration::hours(1));
        time_diff(parse_time("a min ago").unwrap(), Local::now() - Duration::minutes(1));
        time_diff(parse_time("two hours and fifteen minuts ago").unwrap(), Local::now() - Duration::minutes(2 * 60 + 15));
        time_diff(parse_time("two hours and thirty minuts ago").unwrap(), Local::now() - Duration::minutes(2 * 60 + 30));
        // time_diff(parse_time("two and a half hours ago").unwrap(), Local::now() - Duration::minutes(150));
    }
}