use std::collections::HashMap;

use anyhow::{bail, Error};
use lazy_static::lazy_static;
use bitflags::bitflags;

use nom::{
    error::{context, ParseError, VerboseError},
    bytes::complete::{tag, take_while1},
    combinator::{map_res, all_consuming, opt, recognize},
    sequence::{pair, preceded, tuple},
    character::complete::{alpha1, space0, digit1},
    multi::separated_nonempty_list,
};

type IResult<I, O, E = VerboseError<I>> = Result<(I, O), nom::Err<E>>;

fn parse_error<'a>(i: &'a str, context: &'static str) -> nom::Err<VerboseError<&'a str>> {
    let err = VerboseError { errors: Vec::new() };
    let err =VerboseError::add_context(i, context, err);
    nom::Err::Error(err)
}

bitflags!{
    #[derive(Default)]
    pub struct WeekDays: u8 {
        const MONDAY = 1;
        const TUESDAY = 2;
        const WEDNESDAY = 4;
        const THURSDAY = 8;
        const FRIDAY = 16;
        const SATURDAY = 32;
        const SUNDAY = 64;
    }
}

#[derive(Debug)]
pub enum DateTimeValue {
    Single(u32),
    Range(u32, u32),
    Repeated(u32, u32),
}

impl DateTimeValue {
    // Test if the entry contains the value
    pub fn contains(&self, value: u32) -> bool {
        match self {
            DateTimeValue::Single(v) => *v == value,
            DateTimeValue::Range(start, end) => value >= *start && value <= *end,
            DateTimeValue::Repeated(start, repetition) => {
                if *repetition > 0 {
                    let mut found = false;
                    let mut v = *start;
                    loop {
                        if v == value { found = true; break; }
                        v += *repetition;
                        if v > value { break; }
                    }
                    found
                } else {
                    *start == value
                }
            }
        }
    }

    // Find an return an entry greater than value
    pub fn find_next(list: &[DateTimeValue], value: u32) -> Option<u32> {
        let mut next: Option<u32> = None;
        let mut set_next = |v: u32| {
            if let Some(n) = next {
                if v > n { next = Some(v); }
            } else {
                next = Some(v);
            }
        };
        for spec in list {
            match spec {
                DateTimeValue::Single(v) => {
                    if *v > value { set_next(*v); }
                }
                DateTimeValue::Range(start, end) => {
                    if value < *start {
                        set_next(*start);
                    } else {
                        let n = value + 1;
                        if n >= *start && n <= *end {
                            set_next(n);
                        }
                    }
                }
                DateTimeValue::Repeated(start, repetition) => {
                    if value < *start {
                        set_next(*start);
                    } else if *repetition > 0 {
                        let mut v = *start;
                        loop {
                            if v > value { set_next(v); break; }
                            v += *repetition;
                            if v > value { break; }
                        }
                    }
                }
            }
        }

        next
    }
}

#[derive(Default, Debug)]
pub struct CalendarEvent {
    pub days: WeekDays,
    pub second: Vec<DateTimeValue>, // todo: support float values
    pub minute: Vec<DateTimeValue>,
    pub hour: Vec<DateTimeValue>,
}

lazy_static! {
    pub static ref TIME_SPAN_UNITS: HashMap<&'static str, f64> = {
        let mut map = HashMap::new();

        let second = 1.0;

        map.insert("seconds", second);
        map.insert("second", second);
        map.insert("sec", second);
        map.insert("s", second);

        let msec = second / 1000.0;

        map.insert("msec", msec);
        map.insert("ms", msec);

        let usec = msec / 1000.0;

        map.insert("usec", usec);
        map.insert("us", usec);
        map.insert("µs", usec);

        let nsec = usec / 1000.0;

        map.insert("nsec", nsec);
        map.insert("ns", nsec);

        let minute = second * 60.0;

        map.insert("minutes", minute);
        map.insert("minute", minute);
        map.insert("min", minute);
        map.insert("m", minute);

        let hour = minute * 60.0;

        map.insert("hours", hour);
        map.insert("hour", hour);
        map.insert("hr", hour);
        map.insert("h", hour);

        let day = hour * 24.0 ;

        map.insert("days", day);
        map.insert("day", day);
        map.insert("d", day);

        let week = day * 7.0;

        map.insert("weeks", week);
        map.insert("week", week);
        map.insert("w", week);

        let month = 30.44 * day;

        map.insert("months", month);
        map.insert("month", month);
        map.insert("M", month);

        let year = 365.25 * day;

        map.insert("years", year);
        map.insert("year", year);
        map.insert("y", year);

        map
    };
}

#[derive(Default)]
pub struct TimeSpan {
    pub nsec: u64,
    pub usec: u64,
    pub msec: u64,
    pub seconds: u64,
    pub minutes: u64,
    pub hours: u64,
    pub days: u64,
    pub weeks: u64,
    pub months: u64,
    pub years: u64,
}

impl TimeSpan {

    pub fn  new() -> Self {
        Self::default()
    }
}

impl From<TimeSpan> for f64 {
    fn from(ts: TimeSpan) -> Self {
        (ts.seconds as f64) +
            ((ts.nsec as f64) / 1_000_000_000.0)  +
            ((ts.usec as f64) / 1_000_000.0)  +
            ((ts.msec as f64) / 1_000.0)  +
            ((ts.minutes as f64) * 60.0)  +
            ((ts.hours as f64) * 3600.0)  +
            ((ts.days as f64) * 3600.0 * 24.0)  +
            ((ts.weeks as f64) * 3600.0 * 24.0 * 7.0)  +
            ((ts.months as f64) * 3600.0 * 24.0 * 30.44)  +
            ((ts.years as f64) * 3600.0 * 24.0 * 365.25)
    }
}

fn parse_u32(i: &str) -> IResult<&str, u32> {
    map_res(recognize(digit1), str::parse)(i)
}

fn parse_u64(i: &str) -> IResult<&str, u64> {
    map_res(recognize(digit1), str::parse)(i)
}

fn parse_weekday(i: &str) -> IResult<&str, WeekDays, VerboseError<&str>> {
    let (i, text) = alpha1(i)?;

    match text.to_ascii_lowercase().as_str() {
        "monday" | "mon" => Ok((i, WeekDays::MONDAY)),
        "tuesday" | "tue" => Ok((i, WeekDays::TUESDAY)),
        "wednesday" | "wed" => Ok((i, WeekDays::WEDNESDAY)),
        "thursday" | "thu" => Ok((i, WeekDays::THURSDAY)),
        "friday" | "fri" => Ok((i, WeekDays::FRIDAY)),
        "saturday" | "sat" => Ok((i, WeekDays::SATURDAY)),
        "sunday" | "sun" => Ok((i, WeekDays::SUNDAY)),
        _ => return Err(parse_error(text, "weekday")),
    }
}

fn parse_weekdays_range(i: &str) -> IResult<&str, WeekDays> {
    let (i, startday) = parse_weekday(i)?;

    let generate_range = |start, end| {
        let mut res = 0;
        let mut pos = start;
        loop {
            res |= pos;
            if pos >= end { break; }
            pos = pos << 1;
        }
        WeekDays::from_bits(res).unwrap()
    };

    if let (i, Some((_, endday))) = opt(pair(tag(".."),parse_weekday))(i)? {
        let start = startday.bits();
        let end = endday.bits();
        if start > end {
            let set1 = generate_range(start, WeekDays::SUNDAY.bits());
            let set2 = generate_range(WeekDays::MONDAY.bits(), end);
            Ok((i, set1 | set2))
        } else {
            Ok((i, generate_range(start, end)))
        }
    } else {
        Ok((i, startday))
    }
}

fn parse_date_time_comp(i: &str) -> IResult<&str, DateTimeValue> {

    let (i, value) = parse_u32(i)?;

    if let (i, Some(end)) = opt(preceded(tag(".."), parse_u32))(i)? {
        return Ok((i, DateTimeValue::Range(value, end)))
    }

    if i.starts_with("/") {
        let i = &i[1..];
        let (i, repeat) = parse_u32(i)?;
        Ok((i, DateTimeValue::Repeated(value, repeat)))
    } else {
        Ok((i, DateTimeValue::Single(value)))
    }
}

fn parse_date_time_comp_list(i: &str) -> IResult<&str, Vec<DateTimeValue>> {

    if i.starts_with("*") {
        return Ok((&i[1..], Vec::new()));
    }

    separated_nonempty_list(tag(","), parse_date_time_comp)(i)
}

fn parse_time_spec(i: &str) -> IResult<&str, (Vec<DateTimeValue>, Vec<DateTimeValue>, Vec<DateTimeValue>)> {

    let (i, (hour, minute, opt_second)) = tuple((
        parse_date_time_comp_list,
        preceded(tag(":"), parse_date_time_comp_list),
        opt(preceded(tag(":"), parse_date_time_comp_list)),
    ))(i)?;

    if let Some(second) = opt_second {
        Ok((i, (hour, minute, second)))
    } else {
        Ok((i, (hour, minute, vec![DateTimeValue::Single(0)])))
    }
}

pub fn parse_calendar_event(i: &str) -> Result<CalendarEvent, Error> {
    match all_consuming(parse_calendar_event_incomplete)(i) {
        Err(err) => bail!("unable to parse calendar event: {}", err),
        Ok((_, ce)) => Ok(ce),
    }
}

fn parse_calendar_event_incomplete(mut i: &str) -> IResult<&str, CalendarEvent> {

    let mut has_dayspec = false;
    let mut has_timespec = false;
    let has_datespec = false;

    let mut event = CalendarEvent::default();

    if i.starts_with(|c: char| char::is_ascii_alphabetic(&c)) {

        match i {
            "minutely" => {
                return Ok(("", CalendarEvent {
                    second: vec![DateTimeValue::Single(0)],
                    ..Default::default()
                }));
            }
            "hourly" => {
                return Ok(("", CalendarEvent {
                    minute: vec![DateTimeValue::Single(0)],
                    second: vec![DateTimeValue::Single(0)],
                    ..Default::default()
                }));
            }
            "daily" => {
                return Ok(("", CalendarEvent {
                    hour: vec![DateTimeValue::Single(0)],
                    minute: vec![DateTimeValue::Single(0)],
                    second: vec![DateTimeValue::Single(0)],
                    ..Default::default()
                }));
            }
            "monthly" | "weekly" | "yearly" | "quarterly" | "semiannually" => {
                unimplemented!();
            }
            _ => { /* continue */ }
        }

        let (n, range_list) =  context(
            "weekday range list",
            separated_nonempty_list(tag(","), parse_weekdays_range)
        )(i)?;

        has_dayspec = true;

        i = space0(n)?.0;

        for range in range_list  { event.days.insert(range); }
    }

    // todo: support date specs

    if let (n, Some((hour, minute, second))) = opt(parse_time_spec)(i)? {
        event.hour = hour;
        event.minute = minute;
        event.second = second;
        has_timespec = true;
        i = n;
    } else {
        event.hour = vec![DateTimeValue::Single(0)];
        event.minute = vec![DateTimeValue::Single(0)];
        event.second = vec![DateTimeValue::Single(0)];
    }

    if !(has_dayspec || has_timespec || has_datespec) {
        return Err(parse_error(i, "date or time specification"));
    }

    Ok((i, event))
}

fn parse_time_unit(i: &str) ->  IResult<&str, &str> {
    let (n, text) = take_while1(|c: char| char::is_ascii_alphabetic(&c) || c == 'µ')(i)?;
    if TIME_SPAN_UNITS.contains_key(&text) {
        Ok((n, text))
    } else {
        Err(parse_error(text, "time unit"))
    }
}


pub fn parse_time_span(i: &str) -> Result<TimeSpan, Error> {
    match all_consuming(parse_time_span_incomplete)(i) {
        Err(err) => bail!("unable to parse time span: {}", err),
        Ok((_, ts)) => Ok(ts),
    }
}

fn parse_time_span_incomplete(mut i: &str) -> IResult<&str, TimeSpan> {

    let mut ts = TimeSpan::default();

    loop {
        i = space0(i)?.0;
        if i.is_empty() { break; }
        let (n, num) = parse_u64(i)?;
        i = space0(n)?.0;

        if let (n, Some(unit)) = opt(parse_time_unit)(i)? {
            i = n;
            match unit {
                "seconds" | "second" | "sec" | "s" => {
                    ts.seconds += num;
                }
                "msec" | "ms" => {
                    ts.msec += num;
                }
                "usec" | "us" | "µs" => {
                    ts.usec += num;
                }
                "nsec" | "ns" => {
                    ts.nsec += num;
                }
                "minutes" | "minute" | "min" | "m" => {
                    ts.minutes += num;
                }
                "hours" | "hour" | "hr" | "h" => {
                    ts.hours += num;
                }
                "days" | "day" | "d" => {
                    ts.days += num;
                }
                "weeks" | "week" | "w" => {
                    ts.weeks += num;
                }
                "months" | "month" | "M" => {
                    ts.months += num;
                }
                "years" | "year" | "y" => {
                    ts.years += num;
                }
                _ => return Err(parse_error(unit, "internal error")),
            }
        } else {
            ts.seconds += num;
        }
    }

    Ok((i, ts))
}

pub fn verify_time_span<'a>(i: &'a str) -> Result<(), Error> {
    parse_time_span(i)?;
    Ok(())
}

pub fn verify_calendar_event(i: &str) -> Result<(), Error> {
    parse_calendar_event(i)?;
    Ok(())
}

#[cfg(test)]
mod test {

    use super::*;

    fn test_event(v: &'static str) -> Result<(), Error> {
        match parse_calendar_event(v) {
            Ok(event) => println!("CalendarEvent '{}' => {:?}", v, event),
            Err(err) => bail!("parsing '{}' failed - {}", v, err),
        }

        Ok(())
    }

    #[test]
    fn test_calendar_event_weekday() -> Result<(), Error> {
        test_event("mon,wed..fri")?;
        test_event("fri..mon")?;

        test_event("mon")?;
        test_event("MON")?;
        test_event("monDay")?;
        test_event("tue")?;
        test_event("Tuesday")?;
        test_event("wed")?;
        test_event("wednesday")?;
        test_event("thu")?;
        test_event("thursday")?;
        test_event("fri")?;
        test_event("friday")?;
        test_event("sat")?;
        test_event("saturday")?;
        test_event("sun")?;
        test_event("sunday")?;

        test_event("mon..fri")?;
        test_event("mon,tue,fri")?;
        test_event("mon,tue..wednesday,fri..sat")?;

        Ok(())
    }

    #[test]
    fn test_time_span_parser() -> Result<(), Error> {

        let test_value = |ts_str: &str, expect: f64| -> Result<(), Error> {
            let ts = parse_time_span(ts_str)?;
            assert_eq!(f64::from(ts), expect, "{}", ts_str);
            Ok(())
        };

        test_value("2", 2.0)?;
        test_value("2s", 2.0)?;
        test_value("2sec", 2.0)?;
        test_value("2second", 2.0)?;
        test_value("2seconds", 2.0)?;

        test_value(" 2s 2 s 2", 6.0)?;

        test_value("1msec 1ms", 0.002)?;
        test_value("1usec 1us 1µs", 0.000_003)?;
        test_value("1nsec 1ns", 0.000_000_002)?;
        test_value("1minutes 1minute 1min 1m", 4.0*60.0)?;
        test_value("1hours 1hour 1hr 1h", 4.0*3600.0)?;
        test_value("1days 1day 1d", 3.0*86400.0)?;
        test_value("1weeks 1 week 1w", 3.0*86400.0*7.0)?;
        test_value("1months 1month 1M", 3.0*86400.0*30.44)?;
        test_value("1years 1year 1y", 3.0*86400.0*365.25)?;

        test_value("2h", 7200.0)?;
        test_value(" 2 h", 7200.0)?;
        test_value("2hours", 7200.0)?;
        test_value("48hr", 48.0*3600.0)?;
        test_value("1y 12month", 365.25*24.0*3600.0 + 12.0*30.44*24.0*3600.0)?;
        test_value("55s500ms", 55.5)?;
        test_value("300ms20s 5day", 5.0*24.0*3600.0 + 20.0 + 0.3)?;

        Ok(())
    }
}