//! The low-level parsers for date, datetime, duration and time.
//!
//! The top-level functions [`date`][`crate::date`], [`datetime`][`crate::datetime`],
//! [`duration`][`crate::duration`] and [`time`][`crate::time`]
//! provide convenient wrappers around the low-level parsers,
//! but throw away leftover input on success.
//!
//! Using the low-level functions provided here allows to recover leftover input
//! or to combine these parsers with other parser combinators.

use core::str;

use nom::{
    branch::alt,
    bytes::complete::{tag, take_while, take_while_m_n},
    character::complete::one_of,
    character::is_digit,
    combinator::{map, map_res, not, opt},
    error::Error,
    sequence::{preceded, separated_pair, terminated, tuple},
    Err, IResult,
};

use crate::{Date, DateTime, Duration, Time};

#[cfg(test)]
mod tests;

// UTILITY

fn take_digits(i: &[u8]) -> IResult<&[u8], u32> {
    let (i, digits) = take_while(is_digit)(i)?;

    if digits.is_empty() {
        return Err(Err::Error(Error::new(i, nom::error::ErrorKind::Eof)));
    }

    let s = str::from_utf8(digits).expect("Invalid data, expected UTF-8 string");
    let res = s
        .parse()
        .expect("Invalid string, expected ASCII representation of a number");

    Ok((i, res))
}

fn take_n_digits(i: &[u8], n: usize) -> IResult<&[u8], u32> {
    let (i, digits) = take_while_m_n(n, n, is_digit)(i)?;

    let s = str::from_utf8(digits).expect("Invalid data, expected UTF-8 string");
    let res = s
        .parse()
        .expect("Invalid string, expected ASCII representation of a number");

    Ok((i, res))
}

fn n_digit_in_range(
    i: &[u8],
    n: usize,
    range: impl core::ops::RangeBounds<u32>,
) -> IResult<&[u8], u32> {
    let (new_i, number) = take_n_digits(i, n)?;

    if range.contains(&number) {
        Ok((new_i, number))
    } else {
        Err(Err::Error(Error::new(i, nom::error::ErrorKind::Eof)))
    }
}

fn sign(i: &[u8]) -> IResult<&[u8], i32> {
    map(alt((tag(b"-"), tag(b"+"))), |s: &[u8]| match s {
        b"-" => -1,
        _ => 1,
    })(i)
}

// DATE

// [+/-]YYYY
fn date_year(i: &[u8]) -> IResult<&[u8], i32> {
    // The sign is optional, but defaults to `+`
    map(
        tuple((
            opt(sign),               // [+/-]
            |i| take_n_digits(i, 4), // year
        )),
        |(s, year)| s.unwrap_or(1) * year as i32,
    )(i)
}

// MM
fn date_month(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 2, 1..=12)
}

// DD
fn date_day(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 2, 1..=31)
}

// WW
fn date_week(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 2, 1..=52)
}

fn date_week_day(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 1, 1..=7)
}

// ordinal DDD
fn date_ord_day(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 3, 1..=366)
}

// YYYY-MM-DD
fn date_ymd(i: &[u8]) -> IResult<&[u8], Date> {
    map(
        tuple((
            date_year,      // YYYY
            opt(tag(b"-")), // -
            date_month,     // MM
            opt(tag(b"-")), // -
            date_day,       //DD
        )),
        |(year, _, month, _, day)| Date::YMD { year, month, day },
    )(i)
}

// YYYY-DDD
fn date_ordinal(i: &[u8]) -> IResult<&[u8], Date> {
    map(
        separated_pair(date_year, opt(tag(b"-")), date_ord_day),
        |(year, ddd)| Date::Ordinal { year, ddd },
    )(i)
}

// YYYY-"W"WW-D
fn date_iso_week(i: &[u8]) -> IResult<&[u8], Date> {
    map(
        tuple((
            date_year,                          // y
            tuple((opt(tag(b"-")), tag(b"W"))), // [-]W
            date_week,                          // w
            opt(tag(b"-")),                     // [-]
            date_week_day,                      // d
        )),
        |(year, _, ww, _, d)| Date::Week { year, ww, d },
    )(i)
}

/// Parses a date string.
///
/// See [`date`][`crate::date`] for the supported formats.
pub fn parse_date(i: &[u8]) -> IResult<&[u8], Date> {
    alt((date_ymd, date_iso_week, date_ordinal))(i)
}

// TIME

// HH
fn time_hour(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 2, 0..=24)
}

// MM
fn time_minute(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 2, 0..=59)
}

// SS
fn time_second(i: &[u8]) -> IResult<&[u8], u32> {
    n_digit_in_range(i, 2, 0..=60)
}

// Converts the fractional part if-any of a number of seconds to milliseconds
// truncating towards zero if there are more than three digits.
// e.g. "" -> 0, "1" -> 100, "12" -> 120, "123" -> 123, "1234" -> 123
fn fraction_millisecond(i: &[u8]) -> IResult<&[u8], u32> {
    let (i, mut digits) = take_while(is_digit)(i)?;
    let mut l = digits.len();
    if l > 3 {
        digits = digits.get(0..3).unwrap();
    }
    let mut result = 0;
    if l > 0 {
        let digits = str::from_utf8(digits).unwrap(); // This can't panic, `digits` will only include digits.
        result = digits.parse().unwrap();
    }
    while l < 3 {
        result *= 10;
        l += 1;
    }
    Ok((i, result))
}

/// Parses a time string.
///
/// See [`time`][`crate::time`] for the supported formats.
// HH:MM:[SS][.(m*)][(Z|+...|-...)]
pub fn parse_time(i: &[u8]) -> IResult<&[u8], Time> {
    map(
        tuple((
            time_hour,                                         // HH
            opt(tag(b":")),                                    // :
            time_minute,                                       // MM
            opt(preceded(opt(tag(b":")), time_second)),        // [SS]
            opt(preceded(one_of(",."), fraction_millisecond)), // [.(m*)]
            opt(alt((timezone_hour, timezone_utc))),           // [(Z|+...|-...)]
        )),
        |(h, _, m, s, ms, z)| {
            let (tz_offset_hours, tz_offset_minutes) = z.unwrap_or((0, 0));

            Time {
                hour: h,
                minute: m,
                second: s.unwrap_or(0),
                millisecond: ms.unwrap_or(0),
                tz_offset_hours,
                tz_offset_minutes,
            }
        },
    )(i)
}

fn timezone_hour(i: &[u8]) -> IResult<&[u8], (i32, i32)> {
    map(
        tuple((sign, time_hour, opt(preceded(opt(tag(b":")), time_minute)))),
        |(s, h, m)| (s * (h as i32), s * (m.unwrap_or(0) as i32)),
    )(i)
}

fn timezone_utc(i: &[u8]) -> IResult<&[u8], (i32, i32)> {
    map(tag(b"Z"), |_| (0, 0))(i)
}

/// Parses a datetime string.
///
/// See [`datetime`][`crate::datetime`] for supported formats.
// Full ISO8601 datetime
pub fn parse_datetime(i: &[u8]) -> IResult<&[u8], DateTime> {
    map(
        separated_pair(parse_date, tag(b"T"), parse_time),
        |(d, t)| DateTime { date: d, time: t },
    )(i)
}

// DURATION

///    dur-year          = 1*DIGIT "Y" [dur-month]
fn duration_year(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"Y"))(i)
}

///    dur-month         = 1*DIGIT "M" [dur-day]
fn duration_month(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"M"))(i)
}

///    dur-week          = 1*DIGIT "W"
fn duration_week(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"W"))(i)
}

//    dur-day           = 1*DIGIT "D"
fn duration_day(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"D"))(i)
}

///    dur-hour          = 1*DIGIT "H" [dur-minute]
///    dur-time          = "T" (dur-hour / dur-minute / dur-second)
fn duration_hour(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"H"))(i)
}

///    dur-minute        = 1*DIGIT "M" [dur-second]
fn duration_minute(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"M"))(i)
}

////    dur-second        = 1*DIGIT "S"
fn duration_second(i: &[u8]) -> IResult<&[u8], u32> {
    terminated(take_digits, tag(b"S"))(i)
}

///    dur-second-ext    = 1*DIGIT (,|.) 1*DIGIT "S"
fn duration_second_and_millisecond(i: &[u8]) -> IResult<&[u8], (u32, u32)> {
    alt((
        // no milliseconds
        map(duration_second, |m| (m, 0)),
        terminated(
            // with milliseconds
            separated_pair(take_digits, one_of(",."), fraction_millisecond),
            tag(b"S"),
        ),
    ))(i)
}

fn duration_time(i: &[u8]) -> IResult<&[u8], (u32, u32, u32, u32)> {
    map(
        tuple((
            opt(duration_hour),
            opt(duration_minute),
            opt(duration_second_and_millisecond),
        )),
        |(h, m, s)| {
            let (s, ms) = s.unwrap_or((0, 0));

            (h.unwrap_or(0), m.unwrap_or(0), s, ms)
        },
    )(i)
}

fn duration_ymdhms(i: &[u8]) -> IResult<&[u8], Duration> {
    map_res(
        preceded(
            tag(b"P"),
            tuple((
                opt(duration_year),
                opt(duration_month),
                opt(duration_day),
                opt(preceded(tag(b"T"), duration_time)),
            )),
        ),
        |(y, mo, d, time)| {
            // at least one element must be present for a valid duration representation
            if y.is_none() && mo.is_none() && d.is_none() && time.is_none() {
                return Err(Err::Error((i, nom::error::ErrorKind::Eof)));
            }

            let (h, mi, s, ms) = time.unwrap_or((0, 0, 0, 0));

            Ok(Duration::YMDHMS {
                year: y.unwrap_or(0),
                month: mo.unwrap_or(0),
                day: d.unwrap_or(0),
                hour: h,
                minute: mi,
                second: s,
                millisecond: ms,
            })
        },
    )(i)
}

fn duration_weeks(i: &[u8]) -> IResult<&[u8], Duration> {
    map(preceded(tag(b"P"), duration_week), Duration::Weeks)(i)
}

// YYYY, no sign
fn duration_datetime_year(i: &[u8]) -> IResult<&[u8], u32> {
    take_n_digits(i, 4)
}

fn duration_datetime(i: &[u8]) -> IResult<&[u8], Duration> {
    map(
        preceded(
            tuple((tag(b"P"), not(sign))),
            tuple((
                duration_datetime_year,
                opt(tag(b"-")),
                date_month,
                opt(tag(b"-")),
                date_day,
                tag(b"T"),
                parse_time,
            )),
        ),
        |(year, _, month, _, day, _, t)| Duration::YMDHMS {
            year,
            month,
            day,
            hour: t.hour,
            minute: t.minute,
            second: t.second,
            millisecond: t.millisecond,
        },
    )(i)
}

/// Parses a duration string.
///
/// See [`duration`][`crate::duration`] for supported formats.
pub fn parse_duration(i: &[u8]) -> IResult<&[u8], Duration> {
    alt((duration_ymdhms, duration_weeks, duration_datetime))(i)
}