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    // This is a part of Chrono.
    // See README.md and LICENSE.txt for details.

    /*!
     * Various scanning routines for the parser.
     */

    #![allow(deprecated)]

    use super::{ParseResult, INVALID, OUT_OF_RANGE, TOO_SHORT};
    use Weekday;

    /// Returns true when two slices are equal case-insensitively (in ASCII).
    /// Assumes that the `pattern` is already converted to lower case.
    fn equals(s: &str, pattern: &str) -> bool {
        let mut xs = s.as_bytes().iter().map(|&c| match c {
            b'A'...b'Z' => c + 32,
            _ => c,
        });
        let mut ys = pattern.as_bytes().iter().cloned();
        loop {
            match (xs.next(), ys.next()) {
                (None, None) => return true,
                (None, _) | (_, None) => return false,
                (Some(x), Some(y)) if x != y => return false,
                _ => (),
            }
        }
    }

    /// Tries to parse the non-negative number from `min` to `max` digits.
    ///
    /// The absence of digits at all is an unconditional error.
    /// More than `max` digits are consumed up to the first `max` digits.
    /// Any number that does not fit in `i64` is an error.
    #[inline]
    pub fn number(s: &str, min: usize, max: usize) -> ParseResult<(&str, i64)> {
        assert!(min <= max);

        // We are only interested in ascii numbers, so we can work with the `str` as bytes. We stop on
        // the first non-numeric byte, which may be another ascii character or beginning of multi-byte
        // UTF-8 character.
        let bytes = s.as_bytes();
        if bytes.len() < min {
            return Err(TOO_SHORT);
        }

        let mut n = 0i64;
        for (i, c) in bytes.iter().take(max).cloned().enumerate() {
            // cloned() = copied()
            if c < b'0' || b'9' < c {
                if i < min {
                    return Err(INVALID);
                } else {
                    return Ok((&s[i..], n));
                }
            }

            n = match n.checked_mul(10).and_then(|n| n.checked_add((c - b'0') as i64)) {
                Some(n) => n,
                None => return Err(OUT_OF_RANGE),
            };
        }

        Ok((&s[::core::cmp::min(max, bytes.len())..], n))
    }

    /// Tries to consume at least one digits as a fractional second.
    /// Returns the number of whole nanoseconds (0--999,999,999).
    pub fn nanosecond(s: &str) -> ParseResult<(&str, i64)> {
        // record the number of digits consumed for later scaling.
        let origlen = s.len();
        let (s, v) = number(s, 1, 9)?;
        let consumed = origlen - s.len();

        // scale the number accordingly.
        static SCALE: [i64; 10] =
            [0, 100_000_000, 10_000_000, 1_000_000, 100_000, 10_000, 1_000, 100, 10, 1];
        let v = v.checked_mul(SCALE[consumed]).ok_or(OUT_OF_RANGE)?;

        // if there are more than 9 digits, skip next digits.
        let s = s.trim_left_matches(|c: char| '0' <= c && c <= '9');

        Ok((s, v))
    }

    /// Tries to consume a fixed number of digits as a fractional second.
    /// Returns the number of whole nanoseconds (0--999,999,999).
    pub fn nanosecond_fixed(s: &str, digits: usize) -> ParseResult<(&str, i64)> {
        // record the number of digits consumed for later scaling.
        let (s, v) = number(s, digits, digits)?;

        // scale the number accordingly.
        static SCALE: [i64; 10] =
            [0, 100_000_000, 10_000_000, 1_000_000, 100_000, 10_000, 1_000, 100, 10, 1];
        let v = v.checked_mul(SCALE[digits]).ok_or(OUT_OF_RANGE)?;

        Ok((s, v))
    }

    /// Tries to parse the month index (0 through 11) with the first three ASCII letters.
    pub fn short_month0(s: &str) -> ParseResult<(&str, u8)> {
        if s.len() < 3 {
            return Err(TOO_SHORT);
        }
        let buf = s.as_bytes();
        let month0 = match (buf[0] | 32, buf[1] | 32, buf[2] | 32) {
            (b'j', b'a', b'n') => 0,
            (b'f', b'e', b'b') => 1,
            (b'm', b'a', b'r') => 2,
            (b'a', b'p', b'r') => 3,
            (b'm', b'a', b'y') => 4,
            (b'j', b'u', b'n') => 5,
            (b'j', b'u', b'l') => 6,
            (b'a', b'u', b'g') => 7,
            (b's', b'e', b'p') => 8,
            (b'o', b'c', b't') => 9,
            (b'n', b'o', b'v') => 10,
            (b'd', b'e', b'c') => 11,
            _ => return Err(INVALID),
        };
        Ok((&s[3..], month0))
    }

    /// Tries to parse the weekday with the first three ASCII letters.
    pub fn short_weekday(s: &str) -> ParseResult<(&str, Weekday)> {
        if s.len() < 3 {
            return Err(TOO_SHORT);
        }
        let buf = s.as_bytes();
        let weekday = match (buf[0] | 32, buf[1] | 32, buf[2] | 32) {
            (b'm', b'o', b'n') => Weekday::Mon,
            (b't', b'u', b'e') => Weekday::Tue,
            (b'w', b'e', b'd') => Weekday::Wed,
            (b't', b'h', b'u') => Weekday::Thu,
            (b'f', b'r', b'i') => Weekday::Fri,
            (b's', b'a', b't') => Weekday::Sat,
            (b's', b'u', b'n') => Weekday::Sun,
            _ => return Err(INVALID),
        };
        Ok((&s[3..], weekday))
    }

    /// Tries to parse the month index (0 through 11) with short or long month names.
    /// It prefers long month names to short month names when both are possible.
    pub fn short_or_long_month0(s: &str) -> ParseResult<(&str, u8)> {
        // lowercased month names, minus first three chars
        static LONG_MONTH_SUFFIXES: [&'static str; 12] =
            ["uary", "ruary", "ch", "il", "", "e", "y", "ust", "tember", "ober", "ember", "ember"];

        let (mut s, month0) = short_month0(s)?;

        // tries to consume the suffix if possible
        let suffix = LONG_MONTH_SUFFIXES[month0 as usize];
        if s.len() >= suffix.len() && equals(&s[..suffix.len()], suffix) {
            s = &s[suffix.len()..];
        }

        Ok((s, month0))
    }

    /// Tries to parse the weekday with short or long weekday names.
    /// It prefers long weekday names to short weekday names when both are possible.
    pub fn short_or_long_weekday(s: &str) -> ParseResult<(&str, Weekday)> {
        // lowercased weekday names, minus first three chars
        static LONG_WEEKDAY_SUFFIXES: [&'static str; 7] =
            ["day", "sday", "nesday", "rsday", "day", "urday", "day"];

        let (mut s, weekday) = short_weekday(s)?;

        // tries to consume the suffix if possible
        let suffix = LONG_WEEKDAY_SUFFIXES[weekday.num_days_from_monday() as usize];
        if s.len() >= suffix.len() && equals(&s[..suffix.len()], suffix) {
            s = &s[suffix.len()..];
        }

        Ok((s, weekday))
    }

    /// Tries to consume exactly one given character.
    pub fn char(s: &str, c1: u8) -> ParseResult<&str> {
        match s.as_bytes().first() {
            Some(&c) if c == c1 => Ok(&s[1..]),
            Some(_) => Err(INVALID),
            None => Err(TOO_SHORT),
        }
    }

    /// Tries to consume one or more whitespace.
    pub fn space(s: &str) -> ParseResult<&str> {
        let s_ = s.trim_left();
        if s_.len() < s.len() {
            Ok(s_)
        } else if s.is_empty() {
            Err(TOO_SHORT)
        } else {
            Err(INVALID)
        }
    }

    /// Consumes any number (including zero) of colon or spaces.
    pub fn colon_or_space(s: &str) -> ParseResult<&str> {
        Ok(s.trim_left_matches(|c: char| c == ':' || c.is_whitespace()))
    }

    /// Tries to parse `[-+]\d\d` continued by `\d\d`. Return an offset in seconds if possible.
    ///
    /// The additional `colon` may be used to parse a mandatory or optional `:`
    /// between hours and minutes, and should return either a new suffix or `Err` when parsing fails.
    pub fn timezone_offset<F>(s: &str, consume_colon: F) -> ParseResult<(&str, i32)>
    where
        F: FnMut(&str) -> ParseResult<&str>,
    {
        timezone_offset_internal(s, consume_colon, false)
    }

    fn timezone_offset_internal<F>(
        mut s: &str,
        mut consume_colon: F,
        allow_missing_minutes: bool,
    ) -> ParseResult<(&str, i32)>
    where
        F: FnMut(&str) -> ParseResult<&str>,
    {
        fn digits(s: &str) -> ParseResult<(u8, u8)> {
            let b = s.as_bytes();
            if b.len() < 2 {
                Err(TOO_SHORT)
            } else {
                Ok((b[0], b[1]))
            }
        }
        let negative = match s.as_bytes().first() {
            Some(&b'+') => false,
            Some(&b'-') => true,
            Some(_) => return Err(INVALID),
            None => return Err(TOO_SHORT),
        };
        s = &s[1..];

        // hours (00--99)
        let hours = match digits(s)? {
            (h1 @ b'0'...b'9', h2 @ b'0'...b'9') => i32::from((h1 - b'0') * 10 + (h2 - b'0')),
            _ => return Err(INVALID),
        };
        s = &s[2..];

        // colons (and possibly other separators)
        s = consume_colon(s)?;

        // minutes (00--59)
        // if the next two items are digits then we have to add minutes
        let minutes = if let Ok(ds) = digits(s) {
            match ds {
                (m1 @ b'0'...b'5', m2 @ b'0'...b'9') => i32::from((m1 - b'0') * 10 + (m2 - b'0')),
                (b'6'...b'9', b'0'...b'9') => return Err(OUT_OF_RANGE),
                _ => return Err(INVALID),
            }
        } else if allow_missing_minutes {
            0
        } else {
            return Err(TOO_SHORT);
        };
        s = match s.len() {
            len if len >= 2 => &s[2..],
            len if len == 0 => s,
            _ => return Err(TOO_SHORT),
        };

        let seconds = hours * 3600 + minutes * 60;
        Ok((s, if negative { -seconds } else { seconds }))
    }

    /// Same as `timezone_offset` but also allows for `z`/`Z` which is the same as `+00:00`.
    pub fn timezone_offset_zulu<F>(s: &str, colon: F) -> ParseResult<(&str, i32)>
    where
        F: FnMut(&str) -> ParseResult<&str>,
    {
        let bytes = s.as_bytes();
        match bytes.first() {
            Some(&b'z') | Some(&b'Z') => Ok((&s[1..], 0)),
            Some(&b'u') | Some(&b'U') => {
                if bytes.len() >= 3 {
                    let (b, c) = (bytes[1], bytes[2]);
                    match (b | 32, c | 32) {
                        (b't', b'c') => Ok((&s[3..], 0)),
                        _ => Err(INVALID),
                    }
                } else {
                    Err(INVALID)
                }
            }
            _ => timezone_offset(s, colon),
        }
    }

    /// Same as `timezone_offset` but also allows for `z`/`Z` which is the same as
    /// `+00:00`, and allows missing minutes entirely.
    pub fn timezone_offset_permissive<F>(s: &str, colon: F) -> ParseResult<(&str, i32)>
    where
        F: FnMut(&str) -> ParseResult<&str>,
    {
        match s.as_bytes().first() {
            Some(&b'z') | Some(&b'Z') => Ok((&s[1..], 0)),
            _ => timezone_offset_internal(s, colon, true),
        }
    }

    /// Same as `timezone_offset` but also allows for RFC 2822 legacy timezones.
    /// May return `None` which indicates an insufficient offset data (i.e. `-0000`).
    pub fn timezone_offset_2822(s: &str) -> ParseResult<(&str, Option<i32>)> {
        // tries to parse legacy time zone names
        let upto = s
            .as_bytes()
            .iter()
            .position(|&c| match c {
                b'a'...b'z' | b'A'...b'Z' => false,
                _ => true,
            })
            .unwrap_or_else(|| s.len());
        if upto > 0 {
            let name = &s[..upto];
            let s = &s[upto..];
            let offset_hours = |o| Ok((s, Some(o * 3600)));
            if equals(name, "gmt") || equals(name, "ut") {
                offset_hours(0)
            } else if equals(name, "edt") {
                offset_hours(-4)
            } else if equals(name, "est") || equals(name, "cdt") {
                offset_hours(-5)
            } else if equals(name, "cst") || equals(name, "mdt") {
                offset_hours(-6)
            } else if equals(name, "mst") || equals(name, "pdt") {
                offset_hours(-7)
            } else if equals(name, "pst") {
                offset_hours(-8)
            } else {
                Ok((s, None)) // recommended by RFC 2822: consume but treat it as -0000
            }
        } else {
            let (s_, offset) = timezone_offset(s, |s| Ok(s))?;
            Ok((s_, Some(offset)))
        }
    }

    /// Tries to consume everyting until next whitespace-like symbol.
    /// Does not provide any offset information from the consumed data.
    pub fn timezone_name_skip(s: &str) -> ParseResult<(&str, ())> {
        Ok((s.trim_left_matches(|c: char| !c.is_whitespace()), ()))
    }