//! Parse parts of an ISO 8601-formatted value.

use num_conv::prelude::*;

use crate::convert::*;

use crate::error;

use crate::error::ParseFromDescription::{InvalidComponent, InvalidLiteral};

use crate::format_description::well_known::iso8601::EncodedConfig;

use crate::format_description::well_known::Iso8601;

use crate::parsing::combinator::rfc::iso8601::{

    day, dayk, dayo, float, hour, min, month, week, year, ExtendedKind,

};

use crate::parsing::combinator::{ascii_char, sign};

use crate::parsing::{Parsed, ParsedItem};

impl<const CONFIG: EncodedConfig> Iso8601<CONFIG> {

    // Basic: [year][month][day]

    // Extended: [year]["-"][month]["-"][day]

    // Basic: [year][dayo]

    // Extended: [year]["-"][dayo]

    // Basic: [year]["W"][week][dayk]

    // Extended: [year]["-"]["W"][week]["-"][dayk]

    /// Parse a date in the basic or extended format. Reduced precision is permitted.

    pub(crate) fn parse_date<'a>(

        parsed: &'a mut Parsed,

        extended_kind: &'a mut ExtendedKind,

    ) -> impl FnMut(&[u8]) -> Result<&[u8], error::Parse> + 'a {

        move |input| {

            // Same for any acceptable format.

            let ParsedItem(mut input, year) = year(input).ok_or(InvalidComponent("year"))?;

            *extended_kind = match ascii_char::<b'-'>(input) {

                Some(ParsedItem(new_input, ())) => {

                    input = new_input;

                    ExtendedKind::Extended

                }

                None => ExtendedKind::Basic, // no separator before mandatory month/ordinal/week

            };

            let parsed_month_day = (|| {

                let ParsedItem(mut input, month) = month(input).ok_or(InvalidComponent("month"))?;

                if extended_kind.is_extended() {

                    input = ascii_char::<b'-'>(input)

                        .ok_or(InvalidLiteral)?

                        .into_inner();

                }

                let ParsedItem(input, day) = day(input).ok_or(InvalidComponent("day"))?;

                Ok(ParsedItem(input, (month, day)))

            })();

            let mut ret_error = match parsed_month_day {

                Ok(ParsedItem(input, (month, day))) => {

                    *parsed = parsed

                        .with_year(year)

                        .ok_or(InvalidComponent("year"))?

                        .with_month(month)

                        .ok_or(InvalidComponent("month"))?

                        .with_day(day)

                        .ok_or(InvalidComponent("day"))?;

                    return Ok(input);

                }

                Err(err) => err,

            };

            // Don't check for `None`, as the error from year-month-day will always take priority.

            if let Some(ParsedItem(input, ordinal)) = dayo(input) {

                *parsed = parsed

                    .with_year(year)

                    .ok_or(InvalidComponent("year"))?

                    .with_ordinal(ordinal)

                    .ok_or(InvalidComponent("ordinal"))?;

                return Ok(input);

            }

            let parsed_week_weekday = (|| {

                let input = ascii_char::<b'W'>(input)

                    .ok_or((false, InvalidLiteral))?

                    .into_inner();

                let ParsedItem(mut input, week) =

                    week(input).ok_or((true, InvalidComponent("week")))?;

                if extended_kind.is_extended() {

                    input = ascii_char::<b'-'>(input)

                        .ok_or((true, InvalidLiteral))?

                        .into_inner();

                }

                let ParsedItem(input, weekday) =

                    dayk(input).ok_or((true, InvalidComponent("weekday")))?;

                Ok(ParsedItem(input, (week, weekday)))

            })();

            match parsed_week_weekday {

                Ok(ParsedItem(input, (week, weekday))) => {

                    *parsed = parsed

                        .with_iso_year(year)

                        .ok_or(InvalidComponent("year"))?

                        .with_iso_week_number(week)

                        .ok_or(InvalidComponent("week"))?

                        .with_weekday(weekday)

                        .ok_or(InvalidComponent("weekday"))?;

                    return Ok(input);

                }

                Err((false, _err)) => {}

                // This error is more accurate than the one from year-month-day.

                Err((true, err)) => ret_error = err,

            }

            Err(ret_error.into())

        }

    }

    // Basic: ["T"][hour][min][sec]

    // Extended: ["T"][hour][":"][min][":"][sec]

    // Reduced precision: components after [hour] (including their preceding separator) can be

    // omitted. ["T"] can be omitted if there is no date present.

    /// Parse a time in the basic or extended format. Reduced precision is permitted.

    pub(crate) fn parse_time<'a>(

        parsed: &'a mut Parsed,

        extended_kind: &'a mut ExtendedKind,

        date_is_present: bool,

    ) -> impl FnMut(&[u8]) -> Result<&[u8], error::Parse> + 'a {

        move |mut input| {

            if date_is_present {

                input = ascii_char::<b'T'>(input)

                    .ok_or(InvalidLiteral)?

                    .into_inner();

            }

            let ParsedItem(mut input, hour) = float(input).ok_or(InvalidComponent("hour"))?;

            match hour {

                (hour, None) => parsed.set_hour_24(hour).ok_or(InvalidComponent("hour"))?,

                (hour, Some(fractional_part)) => {

                    *parsed = parsed

                        .with_hour_24(hour)

                        .ok_or(InvalidComponent("hour"))?

                        .with_minute((fractional_part * Second::per(Minute) as f64) as _)

                        .ok_or(InvalidComponent("minute"))?

                        .with_second(

                            (fractional_part * Second::per(Hour) as f64 % Minute::per(Hour) as f64)

                                as _,

                        )

                        .ok_or(InvalidComponent("second"))?

                        .with_subsecond(

                            (fractional_part * Nanosecond::per(Hour) as f64

                                % Nanosecond::per(Second) as f64) as _,

                        )

                        .ok_or(InvalidComponent("subsecond"))?;

                    return Ok(input);

                }

            };

            if let Some(ParsedItem(new_input, ())) = ascii_char::<b':'>(input) {

                extended_kind

                    .coerce_extended()

                    .ok_or(InvalidComponent("minute"))?;

                input = new_input;

            };

            let mut input = match float(input) {

                Some(ParsedItem(input, (minute, None))) => {

                    extended_kind.coerce_basic();

                    parsed

                        .set_minute(minute)

                        .ok_or(InvalidComponent("minute"))?;

                    input

                }

                Some(ParsedItem(input, (minute, Some(fractional_part)))) => {

                    // `None` is valid behavior, so don't error if this fails.

                    extended_kind.coerce_basic();

                    *parsed = parsed

                        .with_minute(minute)

                        .ok_or(InvalidComponent("minute"))?

                        .with_second((fractional_part * Second::per(Minute) as f64) as _)

                        .ok_or(InvalidComponent("second"))?

                        .with_subsecond(

                            (fractional_part * Nanosecond::per(Minute) as f64

                                % Nanosecond::per(Second) as f64) as _,

                        )

                        .ok_or(InvalidComponent("subsecond"))?;

                    return Ok(input);

                }

                // colon was present, so minutes are required

                None if extended_kind.is_extended() => {

                    return Err(error::Parse::ParseFromDescription(InvalidComponent(

                        "minute",

                    )));

                }

                None => {

                    // Missing components are assumed to be zero.

                    *parsed = parsed

                        .with_minute(0)

                        .ok_or(InvalidComponent("minute"))?

                        .with_second(0)

                        .ok_or(InvalidComponent("second"))?

                        .with_subsecond(0)

                        .ok_or(InvalidComponent("subsecond"))?;

                    return Ok(input);

                }

            };

            if extended_kind.is_extended() {

                match ascii_char::<b':'>(input) {

                    Some(ParsedItem(new_input, ())) => input = new_input,

                    None => {

                        *parsed = parsed

                            .with_second(0)

                            .ok_or(InvalidComponent("second"))?

                            .with_subsecond(0)

                            .ok_or(InvalidComponent("subsecond"))?;

                        return Ok(input);

                    }

                }

            }

            let (input, second, subsecond) = match float(input) {

                Some(ParsedItem(input, (second, None))) => (input, second, 0),

                Some(ParsedItem(input, (second, Some(fractional_part)))) => (

                    input,

                    second,

                    round(fractional_part * Nanosecond::per(Second) as f64) as _,

                ),

                None if extended_kind.is_extended() => {

                    return Err(error::Parse::ParseFromDescription(InvalidComponent(

                        "second",

                    )));

                }

                // Missing components are assumed to be zero.

                None => (input, 0, 0),

            };

            *parsed = parsed

                .with_second(second)

                .ok_or(InvalidComponent("second"))?

                .with_subsecond(subsecond)

                .ok_or(InvalidComponent("subsecond"))?;

            Ok(input)

        }

    }

    // Basic: [±][hour][min] or ["Z"]

    // Extended: [±][hour][":"][min] or ["Z"]

    // Reduced precision: [±][hour] or ["Z"]

    /// Parse a UTC offset in the basic or extended format. Reduced precision is supported.

    pub(crate) fn parse_offset<'a>(

        parsed: &'a mut Parsed,

        extended_kind: &'a mut ExtendedKind,

    ) -> impl FnMut(&[u8]) -> Result<&[u8], error::Parse> + 'a {

        move |input| {

            if let Some(ParsedItem(input, ())) = ascii_char::<b'Z'>(input) {

                *parsed = parsed

                    .with_offset_hour(0)

                    .ok_or(InvalidComponent("offset hour"))?

                    .with_offset_minute_signed(0)

                    .ok_or(InvalidComponent("offset minute"))?

                    .with_offset_second_signed(0)

                    .ok_or(InvalidComponent("offset second"))?;

                return Ok(input);

            }

            let ParsedItem(input, sign) = sign(input).ok_or(InvalidComponent("offset hour"))?;

            let mut input = hour(input)

                .and_then(|parsed_item| {

                    parsed_item.consume_value(|hour| {

                        parsed.set_offset_hour(if sign == b'-' {

                            -hour.cast_signed()

                        } else {

                            hour.cast_signed()

                        })

                    })

                })

                .ok_or(InvalidComponent("offset hour"))?;

            if extended_kind.maybe_extended() {

                if let Some(ParsedItem(new_input, ())) = ascii_char::<b':'>(input) {

                    extended_kind

                        .coerce_extended()

                        .ok_or(InvalidComponent("offset minute"))?;

                    input = new_input;

                };

            }

            match min(input) {

                Some(ParsedItem(new_input, min)) => {

                    input = new_input;

                    parsed

                        .set_offset_minute_signed(if sign == b'-' {

                            -min.cast_signed()

                        } else {

                            min.cast_signed()

                        })

                        .ok_or(InvalidComponent("offset minute"))?;

                }

                None => {

                    // Omitted offset minute is assumed to be zero.

                    parsed.set_offset_minute_signed(0);

                }

            }

            // If `:` was present, the format has already been set to extended. As such, this call

            // will do nothing in that case. If there wasn't `:` but minutes were

            // present, we know it's the basic format. Do not use `?` on the call, as

            // returning `None` is valid behavior.

            extended_kind.coerce_basic();

            Ok(input)

        }

    }

}

/// Round wrapper that uses hardware implementation if `std` is available, falling back to manual

/// implementation for `no_std`

fn round(value: f64) -> f64 {

    #[cfg(feature = "std")]

    {

        value.round()

    }

    #[cfg(not(feature = "std"))]

    {

        round_impl(value)

    }

}

#[cfg(not(feature = "std"))]

#[allow(clippy::missing_docs_in_private_items)]

fn round_impl(value: f64) -> f64 {

    debug_assert!(value.is_sign_positive() && !value.is_nan());

    let f = value % 1.;

    if f < 0.5 {

        value - f

    } else {

        value - f + 1.

    }

}