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

/*!
`strftime`/`strptime`-inspired date and time formatting syntax.

## Specifiers

The following specifiers are available both to formatting and parsing.

Spec. | Example       | Description
----- | ------------- | -----------
      |               | **DATE SPECIFIERS:**
`%Y`  | `2001`        | The full proleptic Gregorian year, zero-padded to 4 digits. [1]
`%C`  | `20`          | The proleptic Gregorian year divided by 100, zero-padded to 2 digits. [2]
`%y`  | `01`          | The proleptic Gregorian year modulo 100, zero-padded to 2 digits. [2]
      |               |
`%m`  | `07`          | Month number (01--12), zero-padded to 2 digits.
`%b`  | `Jul`         | Abbreviated month name. Always 3 letters.
`%B`  | `July`        | Full month name. Also accepts corresponding abbreviation in parsing.
`%h`  | `Jul`         | Same to `%b`.
      |               |
`%d`  | `08`          | Day number (01--31), zero-padded to 2 digits.
`%e`  | ` 8`          | Same to `%d` but space-padded. Same to `%_d`.
      |               |
`%a`  | `Sun`         | Abbreviated weekday name. Always 3 letters.
`%A`  | `Sunday`      | Full weekday name. Also accepts corresponding abbreviation in parsing.
`%w`  | `0`           | Sunday = 0, Monday = 1, ..., Saturday = 6.
`%u`  | `7`           | Monday = 1, Tuesday = 2, ..., Sunday = 7. (ISO 8601)
      |               |
`%U`  | `28`          | Week number starting with Sunday (00--53), zero-padded to 2 digits. [3]
`%W`  | `27`          | Same to `%U`, but week 1 starts with the first Monday in that year instead.
      |               |
`%G`  | `2001`        | Same to `%Y` but uses the year number in ISO 8601 week date. [4]
`%g`  | `01`          | Same to `%y` but uses the year number in ISO 8601 week date. [4]
`%V`  | `27`          | Same to `%U` but uses the week number in ISO 8601 week date (01--53). [4]
      |               |
`%j`  | `189`         | Day of the year (001--366), zero-padded to 3 digits.
      |               |
`%D`  | `07/08/01`    | Month-day-year format. Same to `%m/%d/%y`.
`%x`  | `07/08/01`    | Same to `%D`.
`%F`  | `2001-07-08`  | Year-month-day format (ISO 8601). Same to `%Y-%m-%d`.
`%v`  | ` 8-Jul-2001` | Day-month-year format. Same to `%e-%b-%Y`.
      |               |
      |               | **TIME SPECIFIERS:**
`%H`  | `00`          | Hour number (00--23), zero-padded to 2 digits.
`%k`  | ` 0`          | Same to `%H` but space-padded. Same to `%_H`.
`%I`  | `12`          | Hour number in 12-hour clocks (01--12), zero-padded to 2 digits.
`%l`  | `12`          | Same to `%I` but space-padded. Same to `%_I`.
      |               |
`%P`  | `am`          | `am` or `pm` in 12-hour clocks.
`%p`  | `AM`          | `AM` or `PM` in 12-hour clocks.
      |               |
`%M`  | `34`          | Minute number (00--59), zero-padded to 2 digits.
`%S`  | `60`          | Second number (00--60), zero-padded to 2 digits. [5]
`%f`  | `026490000`   | The fractional seconds (in nanoseconds) since last whole second. [8]
`%.f` | `.026490`     | Similar to `.%f` but left-aligned. [8]
`%.3f`| `.026`        | Similar to `.%f` but left-aligned but fixed to a length of 3. [8]
`%.6f`| `.026490`     | Similar to `.%f` but left-aligned but fixed to a length of 6. [8]
`%.9f`| `.026490000`  | Similar to `.%f` but left-aligned but fixed to a length of 9. [8]
      |               |
`%R`  | `00:34`       | Hour-minute format. Same to `%H:%M`.
`%T`  | `00:34:60`    | Hour-minute-second format. Same to `%H:%M:%S`.
`%X`  | `00:34:60`    | Same to `%T`.
`%r`  | `12:34:60 AM` | Hour-minute-second format in 12-hour clocks. Same to `%I:%M:%S %p`.
      |               |
      |               | **TIME ZONE SPECIFIERS:**
`%Z`  | `ACST`        | *Formatting only:* Local time zone name.
`%z`  | `+0930`       | Offset from the local time to UTC (with UTC being `+0000`).
`%:z` | `+09:30`      | Same to `%z` but with a colon.
      |               |
      |               | **DATE & TIME SPECIFIERS:**
`%c`  | `Sun Jul  8 00:34:60 2001` | `ctime` date & time format. Same to `%a %b %e %T %Y` sans `\n`.
`%+`  | `2001-07-08T00:34:60.026490+09:30` | ISO 8601 / RFC 3339 date & time format. [6]
      |               |
`%s`  | `994518299`   | UNIX timestamp, the number of seconds since 1970-01-01 00:00 UTC. [7]
      |               |
      |               | **SPECIAL SPECIFIERS:**
`%t`  |               | Literal tab (`\t`).
`%n`  |               | Literal newline (`\n`).
`%%`  |               | Literal percent sign.

It is possible to override the default padding behavior of numeric specifiers `%?`.
This is not allowed for other specifiers and will result in the `BAD_FORMAT` error.

Modifier | Description
-------- | -----------
`%-?`    | Suppresses any padding including spaces and zeroes. (e.g. `%j` = `012`, `%-j` = `12`)
`%_?`    | Uses spaces as a padding. (e.g. `%j` = `012`, `%_j` = ` 12`)
`%0?`    | Uses zeroes as a padding. (e.g. `%e` = ` 9`, `%0e` = `09`)

Notes:

1. `%Y`:
   Negative years are allowed in formatting but not in parsing.

2. `%C`, `%y`:
   This is floor division, so 100 BCE (year number -99) will print `-1` and `99` respectively.

3. `%U`:
   Week 1 starts with the first Sunday in that year.
   It is possible to have week 0 for days before the first Sunday.

4. `%G`, `%g`, `%V`:
   Week 1 is the first week with at least 4 days in that year.
   Week 0 does not exist, so this should be used with `%G` or `%g`.

5. `%S`:
   It accounts for leap seconds, so `60` is possible.

6. `%+`:
   Same to `%Y-%m-%dT%H:%M:%S%.f%:z`,
   i.e. 0, 3, 6 or 9 fractional digits for seconds and colons in the time zone offset.

   The typical `strftime` implementations have
   different (and locale-dependent) formats for this specifier.
   While Chrono's format for `%+` is far more stable,
   it is best to avoid this specifier if you want to control the exact output.

7. `%s`:
   This is not padded and can be negative.
   For the purpose of Chrono, it only accounts for non-leap seconds
   so it slightly differs from ISO C `strftime` behavior.

8. `%f`, `%.f`, `%.3f`, `%.6f`, `%.9f`:

   The default `%f` is right-aligned and always zero-padded to 9 digits
   for the compatibility with glibc and others,
   so it always counts the number of nanoseconds since the last whole second.
   E.g. 7ms after the last second will print `007000000`,
   and parsing `7000000` will yield the same.

   The variant `%.f` is left-aligned and print 0, 3, 6 or 9 fractional digits
   according to the precision.
   E.g. 70ms after the last second under `%.f` will print `.070` (note: not `.07`),
   and parsing `.07`, `.070000` etc. will yield the same.
   Note that they can print or read nothing if the fractional part is zero or
   the next character is not `.`.

   The variant `%.3f`, `%.6f` and `%.9f` are left-aligned and print 3, 6 or 9 fractional digits
   according to the number preceding `f`.
   E.g. 70ms after the last second under `%.3f` will print `.070` (note: not `.07`),
   and parsing `.07`, `.070000` etc. will yield the same.
   Note that they can read nothing if the fractional part is zero or
   the next character is not `.` however will print with the specified length.

*/

use super::{Item, Numeric, Fixed, Pad};

/// Parsing iterator for `strftime`-like format strings.
#[derive(Clone)]
pub struct StrftimeItems<'a> {
    /// Remaining portion of the string.
    remainder: &'a str,
    /// If the current specifier is composed of multiple formatting items (e.g. `%+`),
    /// parser refers to the statically reconstructed slice of them.
    /// If `recons` is not empty they have to be returned earlier than the `remainder`.
    recons: &'static [Item<'static>],
}

impl<'a> StrftimeItems<'a> {
    /// Creates a new parsing iterator from the `strftime`-like format string.
    pub fn new(s: &'a str) -> StrftimeItems<'a> {
        static FMT_NONE: [Item<'static>; 0] = [];
        StrftimeItems { remainder: s, recons: &FMT_NONE }
    }
}

impl<'a> Iterator for StrftimeItems<'a> {
    type Item = Item<'a>;

    fn next(&mut self) -> Option<Item<'a>> {
        // we have some reconstructed items to return
        if !self.recons.is_empty() {
            let item = self.recons[0].clone();
            self.recons = &self.recons[1..];
            return Some(item);
        }

        match self.remainder.chars().next() {
            // we are done
            None => return None,

            // the next item is a specifier
            Some('%') => {
                self.remainder = &self.remainder[1..];

                macro_rules! next {
                    () => (
                        match self.remainder.chars().next() {
                            Some(x) => {
                                self.remainder = &self.remainder[x.len_utf8()..];
                                x
                            },
                            None => return Some(Item::Error), // premature end of string
                        }
                    )
                }

                let spec = next!();
                let pad_override = match spec {
                    '-' => Some(Pad::None),
                    '0' => Some(Pad::Zero),
                    '_' => Some(Pad::Space),
                    _ => None,
                };
                let spec = if pad_override.is_some() { next!() } else { spec };

                macro_rules! recons {
                    [$head:expr, $($tail:expr),+] => ({
                        const RECONS: &'static [Item<'static>] = &[$($tail),+];
                        self.recons = RECONS;
                        $head
                    })
                }

                let item = match spec {
                    'A' => fix!(LongWeekdayName),
                    'B' => fix!(LongMonthName),
                    'C' => num0!(YearDiv100),
                    'D' => recons![num0!(Month), lit!("/"), num0!(Day), lit!("/"),
                                   num0!(YearMod100)],
                    'F' => recons![num0!(Year), lit!("-"), num0!(Month), lit!("-"), num0!(Day)],
                    'G' => num0!(IsoYear),
                    'H' => num0!(Hour),
                    'I' => num0!(Hour12),
                    'M' => num0!(Minute),
                    'P' => fix!(LowerAmPm),
                    'R' => recons![num0!(Hour), lit!(":"), num0!(Minute)],
                    'S' => num0!(Second),
                    'T' => recons![num0!(Hour), lit!(":"), num0!(Minute), lit!(":"), num0!(Second)],
                    'U' => num0!(WeekFromSun),
                    'V' => num0!(IsoWeek),
                    'W' => num0!(WeekFromMon),
                    'X' => recons![num0!(Hour), lit!(":"), num0!(Minute), lit!(":"), num0!(Second)],
                    'Y' => num0!(Year),
                    'Z' => fix!(TimezoneName),
                    'a' => fix!(ShortWeekdayName),
                    'b' => fix!(ShortMonthName),
                    'c' => recons![fix!(ShortWeekdayName), sp!(" "), fix!(ShortMonthName),
                                   sp!(" "), nums!(Day), sp!(" "), num0!(Hour), lit!(":"),
                                   num0!(Minute), lit!(":"), num0!(Second), sp!(" "), num0!(Year)],
                    'd' => num0!(Day),
                    'e' => nums!(Day),
                    'f' => num0!(Nanosecond),
                    'g' => num0!(IsoYearMod100),
                    'h' => fix!(ShortMonthName),
                    'j' => num0!(Ordinal),
                    'k' => nums!(Hour),
                    'l' => nums!(Hour12),
                    'm' => num0!(Month),
                    'n' => sp!("\n"),
                    'p' => fix!(UpperAmPm),
                    'r' => recons![num0!(Hour12), lit!(":"), num0!(Minute), lit!(":"),
                                   num0!(Second), sp!(" "), fix!(UpperAmPm)],
                    's' => num!(Timestamp),
                    't' => sp!("\t"),
                    'u' => num!(WeekdayFromMon),
                    'v' => recons![nums!(Day), lit!("-"), fix!(ShortMonthName), lit!("-"),
                                   num0!(Year)],
                    'w' => num!(NumDaysFromSun),
                    'x' => recons![num0!(Month), lit!("/"), num0!(Day), lit!("/"),
                                   num0!(YearMod100)],
                    'y' => num0!(YearMod100),
                    'z' => fix!(TimezoneOffset),
                    '+' => fix!(RFC3339),
                    ':' => match next!() {
                        'z' => fix!(TimezoneOffsetColon),
                        _ => Item::Error,
                    },
                    '.' => match next!() {
                        '3' => match next!() {
                            'f' => fix!(Nanosecond3),
                            _ => Item::Error,
                        },
                        '6' => match next!() {
                            'f' => fix!(Nanosecond6),
                            _ => Item::Error,
                        },
                        '9' => match next!() {
                            'f' => fix!(Nanosecond9),
                            _ => Item::Error,
                        },
                        'f' => fix!(Nanosecond),
                        _ => Item::Error,
                    },
                    '%' => lit!("%"),
                    _ => Item::Error, // no such specifier
                };

                // adjust `item` if we have any padding modifier
                if let Some(new_pad) = pad_override {
                    match item {
                        Item::Numeric(ref kind, _pad) if self.recons.is_empty() =>
                            Some(Item::Numeric(kind.clone(), new_pad)),
                        _ => Some(Item::Error), // no reconstructed or non-numeric item allowed
                    }
                } else {
                    Some(item)
                }
            },

            // the next item is space
            Some(c) if c.is_whitespace() => {
                // `%` is not a whitespace, so `c != '%'` is redundant
                let nextspec = self.remainder.find(|c: char| !c.is_whitespace())
                                             .unwrap_or(self.remainder.len());
                assert!(nextspec > 0);
                let item = sp!(&self.remainder[..nextspec]);
                self.remainder = &self.remainder[nextspec..];
                Some(item)
            },

            // the next item is literal
            _ => {
                let nextspec = self.remainder.find(|c: char| c.is_whitespace() || c == '%')
                                             .unwrap_or(self.remainder.len());
                assert!(nextspec > 0);
                let item = lit!(&self.remainder[..nextspec]);
                self.remainder = &self.remainder[nextspec..];
                Some(item)
            },
        }
    }
}

#[cfg(test)]
#[test]
fn test_strftime_items() {
    fn parse_and_collect<'a>(s: &'a str) -> Vec<Item<'a>> {
        // map any error into `[Item::Error]`. useful for easy testing.
        let items = StrftimeItems::new(s);
        let items = items.map(|spec| if spec == Item::Error {None} else {Some(spec)});
        items.collect::<Option<Vec<_>>>().unwrap_or(vec![Item::Error])
    }

    assert_eq!(parse_and_collect(""), []);
    assert_eq!(parse_and_collect(" \t\n\r "), [sp!(" \t\n\r ")]);
    assert_eq!(parse_and_collect("hello?"), [lit!("hello?")]);
    assert_eq!(parse_and_collect("a  b\t\nc"), [lit!("a"), sp!("  "), lit!("b"), sp!("\t\n"),
                                                lit!("c")]);
    assert_eq!(parse_and_collect("100%%"), [lit!("100"), lit!("%")]);
    assert_eq!(parse_and_collect("100%% ok"), [lit!("100"), lit!("%"), sp!(" "), lit!("ok")]);
    assert_eq!(parse_and_collect("%%PDF-1.0"), [lit!("%"), lit!("PDF-1.0")]);
    assert_eq!(parse_and_collect("%Y-%m-%d"), [num0!(Year), lit!("-"), num0!(Month), lit!("-"),
                                               num0!(Day)]);
    assert_eq!(parse_and_collect("[%F]"), parse_and_collect("[%Y-%m-%d]"));
    assert_eq!(parse_and_collect("%m %d"), [num0!(Month), sp!(" "), num0!(Day)]);
    assert_eq!(parse_and_collect("%"), [Item::Error]);
    assert_eq!(parse_and_collect("%%"), [lit!("%")]);
    assert_eq!(parse_and_collect("%%%"), [Item::Error]);
    assert_eq!(parse_and_collect("%%%%"), [lit!("%"), lit!("%")]);
    assert_eq!(parse_and_collect("foo%?"), [Item::Error]);
    assert_eq!(parse_and_collect("bar%42"), [Item::Error]);
    assert_eq!(parse_and_collect("quux% +"), [Item::Error]);
    assert_eq!(parse_and_collect("%.Z"), [Item::Error]);
    assert_eq!(parse_and_collect("%:Z"), [Item::Error]);
    assert_eq!(parse_and_collect("%-Z"), [Item::Error]);
    assert_eq!(parse_and_collect("%0Z"), [Item::Error]);
    assert_eq!(parse_and_collect("%_Z"), [Item::Error]);
    assert_eq!(parse_and_collect("%.j"), [Item::Error]);
    assert_eq!(parse_and_collect("%:j"), [Item::Error]);
    assert_eq!(parse_and_collect("%-j"), [num!(Ordinal)]);
    assert_eq!(parse_and_collect("%0j"), [num0!(Ordinal)]);
    assert_eq!(parse_and_collect("%_j"), [nums!(Ordinal)]);
    assert_eq!(parse_and_collect("%.e"), [Item::Error]);
    assert_eq!(parse_and_collect("%:e"), [Item::Error]);
    assert_eq!(parse_and_collect("%-e"), [num!(Day)]);
    assert_eq!(parse_and_collect("%0e"), [num0!(Day)]);
    assert_eq!(parse_and_collect("%_e"), [nums!(Day)]);
}

#[cfg(test)]
#[test]
fn test_strftime_docs() {
    use {FixedOffset, TimeZone};

    let dt = FixedOffset::east(34200).ymd(2001, 7, 8).and_hms_nano(0, 34, 59, 1_026_490_000);

    // date specifiers
    assert_eq!(dt.format("%Y").to_string(), "2001");
    assert_eq!(dt.format("%C").to_string(), "20");
    assert_eq!(dt.format("%y").to_string(), "01");
    assert_eq!(dt.format("%m").to_string(), "07");
    assert_eq!(dt.format("%b").to_string(), "Jul");
    assert_eq!(dt.format("%B").to_string(), "July");
    assert_eq!(dt.format("%h").to_string(), "Jul");
    assert_eq!(dt.format("%d").to_string(), "08");
    assert_eq!(dt.format("%e").to_string(), " 8");
    assert_eq!(dt.format("%e").to_string(), dt.format("%_d").to_string());
    assert_eq!(dt.format("%a").to_string(), "Sun");
    assert_eq!(dt.format("%A").to_string(), "Sunday");
    assert_eq!(dt.format("%w").to_string(), "0");
    assert_eq!(dt.format("%u").to_string(), "7");
    assert_eq!(dt.format("%U").to_string(), "28");
    assert_eq!(dt.format("%W").to_string(), "27");
    assert_eq!(dt.format("%G").to_string(), "2001");
    assert_eq!(dt.format("%g").to_string(), "01");
    assert_eq!(dt.format("%V").to_string(), "27");
    assert_eq!(dt.format("%j").to_string(), "189");
    assert_eq!(dt.format("%D").to_string(), "07/08/01");
    assert_eq!(dt.format("%x").to_string(), "07/08/01");
    assert_eq!(dt.format("%F").to_string(), "2001-07-08");
    assert_eq!(dt.format("%v").to_string(), " 8-Jul-2001");

    // time specifiers
    assert_eq!(dt.format("%H").to_string(), "00");
    assert_eq!(dt.format("%k").to_string(), " 0");
    assert_eq!(dt.format("%k").to_string(), dt.format("%_H").to_string());
    assert_eq!(dt.format("%I").to_string(), "12");
    assert_eq!(dt.format("%l").to_string(), "12");
    assert_eq!(dt.format("%l").to_string(), dt.format("%_I").to_string());
    assert_eq!(dt.format("%P").to_string(), "am");
    assert_eq!(dt.format("%p").to_string(), "AM");
    assert_eq!(dt.format("%M").to_string(), "34");
    assert_eq!(dt.format("%S").to_string(), "60");
    assert_eq!(dt.format("%f").to_string(), "026490000");
    assert_eq!(dt.format("%.f").to_string(), ".026490");
    assert_eq!(dt.format("%.3f").to_string(), ".026");
    assert_eq!(dt.format("%.6f").to_string(), ".026490");
    assert_eq!(dt.format("%.9f").to_string(), ".026490000");
    assert_eq!(dt.format("%R").to_string(), "00:34");
    assert_eq!(dt.format("%T").to_string(), "00:34:60");
    assert_eq!(dt.format("%X").to_string(), "00:34:60");
    assert_eq!(dt.format("%r").to_string(), "12:34:60 AM");

    // time zone specifiers
    //assert_eq!(dt.format("%Z").to_string(), "ACST");
    assert_eq!(dt.format("%z").to_string(), "+0930");
    assert_eq!(dt.format("%:z").to_string(), "+09:30");

    // date & time specifiers
    assert_eq!(dt.format("%c").to_string(), "Sun Jul  8 00:34:60 2001");
    assert_eq!(dt.format("%+").to_string(), "2001-07-08T00:34:60.026490+09:30");
    assert_eq!(dt.format("%s").to_string(), "994518299");

    // special specifiers
    assert_eq!(dt.format("%t").to_string(), "\t");
    assert_eq!(dt.format("%n").to_string(), "\n");
    assert_eq!(dt.format("%%").to_string(), "%");
}