deep-time 0.1.0-beta.3

pub mod parser;

pub(crate) use parser::*;

use crate::error::{DtErr, DtErrKind};
use crate::{Dt, TimeParts, an_err};
use core::result::Result;
use core::str;

#[cfg(feature = "alloc")]
use crate::Scale;

/// A pre-validated, reusable date/time format string.
///
/// - Format is validated **once** at construction (`new` returns `Result`).
/// - Format bytes are copied into an owned fixed-size buffer.
/// - Only ASCII formats are accepted.
///
/// ## See also
///
/// - [`StrPTimeFmt::new`]
/// - [`StrPTimeFmt::to_dt`]
/// - [`StrPTimeFmt::to_str`]
#[derive(Debug, Clone, Copy)]
pub struct StrPTimeFmt {
    fmt: [u8; Self::MAX_FORMAT_LEN],
    len: usize,
}

impl StrPTimeFmt {
    pub const MAX_FORMAT_LEN: usize = 256;

    /// Creates a new validated format.
    ///
    /// - Validates syntax and supported directives.
    /// - Requires the format to be valid ASCII and ≤ 256 bytes.
    /// - Returns a `DtErr` on any failure.
    ///
    /// ## Examples
    ///
    /// ```
    /// # #[cfg(feature = "parse")]
    /// # {
    /// use deep_time::{Dt, StrPTimeFmt};
    ///
    /// let fmt = Dt::parse_fmt("%F %T").unwrap();
    ///
    /// // parse a datetime
    /// let dt = fmt.to_dt("2025-05-23 14:30:00", false, false, false).unwrap();
    ///
    /// // change a datetimes format
    /// let s = fmt.to_str("2000-01-01 12:00:00", "%d %m %Y %H:%M:%S", false, false, false).unwrap();
    /// # }
    /// ```
    pub fn new(fmt: &str) -> Result<Self, DtErr> {
        if fmt.len() > Self::MAX_FORMAT_LEN {
            return Err(an_err!(
                DtErrKind::UnexpectedEnd,
                "format string too long (max {} bytes)",
                Self::MAX_FORMAT_LEN
            ));
        }
        let fmt = fmt.as_bytes();
        if !fmt.is_ascii() {
            return Err(an_err!(
                DtErrKind::UnexpectedEnd,
                "format string must be ASCII"
            ));
        }

        Self::validate_format(fmt)?;

        let mut buffer = [0u8; Self::MAX_FORMAT_LEN];
        buffer[..fmt.len()].copy_from_slice(fmt);

        Ok(Self {
            fmt: buffer,
            len: fmt.len(),
        })
    }

    /// Parses a date/time string using this pre-validated format.
    ///
    /// The four boolean flags control lenient parsing behavior — see
    /// [`Dt::from_str`](../struct.Dt.html#method.from_str) for full documentation.
    ///
    /// ## Parameters
    ///
    /// - `s`: The input string to parse.
    /// - `inp_can_end_before_fmt`: Allow input to end before format is fully consumed.
    /// - `fmt_can_end_before_inp`: Allow format to end before input is fully consumed.
    /// - `allow_partial_date`: Default missing month/day to `1` instead of erroring.
    ///
    /// ## Errors
    ///
    /// Returns [`DtErr`] for parse failures, incomplete data, trailing characters, etc.
    ///
    /// ## Example
    ///
    /// ```
    /// use deep_time::{Dt, StrPTimeFmt};
    ///
    /// let fmt = Dt::parse_fmt("%F %T").unwrap();
    /// let dt = fmt.to_dt("2025-05-23 14:30:00", false, false, false).unwrap();
    /// ```
    pub fn to_dt(
        &self,
        s: &str,
        inp_can_end_before_fmt: bool,
        fmt_can_end_before_inp: bool,
        allow_partial_date: bool,
    ) -> Result<Dt, DtErr> {
        TimeParts::from_str(
            self.as_str()?,
            s,
            inp_can_end_before_fmt,
            fmt_can_end_before_inp,
            allow_partial_date,
        )
        .and_then(|p| p.to_dt())
    }

    /// Formats a [`Dt`] into a string using this pre-validated format and a given
    /// output format.
    ///
    /// Effectively parses a [`str`] with the contained format, then outputs a
    /// [`String`](`alloc::string::String`) to a new given format.
    ///
    /// Requires the `alloc` feature.
    ///
    /// ## Parameters
    ///
    /// - `s`: datetime input [`str`].
    /// - `output_fmt`: The new format to output the datetime as.
    /// - The remaining three flags are passed through to the internal `to_dt` call.
    ///
    /// ## Example
    ///
    /// ```
    /// use deep_time::{Dt, StrPTimeFmt};
    ///
    /// let fmt = Dt::parse_fmt("%Y-%m-%dT%H:%M:%S").unwrap();
    /// let s = fmt.to_str("2000-01-01T12:00:00", "%d %m %Y %H:%M:%S", false, false, false).unwrap();
    /// ```
    #[cfg(feature = "alloc")]
    pub fn to_str(
        &self,
        s: &str,
        output_fmt: &str,
        inp_can_end_before_fmt: bool,
        fmt_can_end_before_inp: bool,
        allow_partial_date: bool,
    ) -> Result<alloc::string::String, DtErr> {
        self.to_dt(
            s,
            inp_can_end_before_fmt,
            fmt_can_end_before_inp,
            allow_partial_date,
        )?
        .to_str(Scale::TAI, output_fmt)
    }

    fn validate_format(mut fmt: &[u8]) -> Result<(), DtErr> {
        while !fmt.is_empty() {
            if fmt[0] != b'%' {
                // literal character (including whitespace) — always valid
                fmt = &fmt[1..];
                continue;
            }

            // lone % at end of format
            if fmt.len() == 1 {
                return Err(an_err!(DtErrKind::UnexpectedEnd, "after %"));
            }
            fmt = &fmt[1..]; // eat %

            // reuse existing helper for flags/width/colons
            let (_, _, _, new_fmt) = Parser::parse_format_extensions(fmt, 0);
            fmt = new_fmt;

            if fmt.is_empty() {
                return Err(an_err!(DtErrKind::UnexpectedEnd, "expected directive"));
            }

            let directive = fmt[0];

            match directive {
            // all currently supported directives
            b'%' | b'A' | b'a' | b'B' | b'b' | b'h' | b'C' | b'd' | b'e' |
            b'f' | b'N' | b'G' | b'g' | b'H' | b'k' | b'I' | b'l' | b'j' |
            b'M' | b'm' | b'n' | b't' | b'P' | b'p' | b'Q' | b'S' | b's' |
            b'U' | b'u' | b'V' | b'W' | b'w' | b'Y' | b'y' | b'z' |
            // shortcuts
            b'F' | b'D' | b'T' | b'R' |
            // library directives
            b'*' => {
                fmt = &fmt[1..];
            }

            b'.' => {
                // special case for %.f / %.3N etc.
                fmt = &fmt[1..]; // eat the .

                // optional width digits
                while !fmt.is_empty() && fmt[0].is_ascii_digit() {
                    fmt = &fmt[1..];
                }

                let next = fmt.first().copied().unwrap_or(0);
                if !matches!(next, b'f' | b'N') {
                    return Err(an_err!(DtErrKind::BadFractional, "{}", char::from(next)));
                }
                fmt = &fmt[1..];
            }

            // explicitly unsupported (same as Parser)
            b'c' | b'r' | b'X' | b'x' | b'Z' => {
                return Err(an_err!(
                    DtErrKind::UnsupportedDirective,
                    "{}",
                    char::from(directive)
                ));
            }

            _ => {
                return Err(an_err!(DtErrKind::UnknownDirective));
            }
        }
        }

        Ok(())
    }

    #[inline]
    fn as_bytes(&self) -> &[u8] {
        &self.fmt[..self.len]
    }

    #[inline]
    fn as_str(&self) -> Result<&str, DtErr> {
        match core::str::from_utf8(self.as_bytes()) {
            Ok(f) => Ok(f),
            Err(e) => Err(an_err!(DtErrKind::InvalidBytes, "{}", e)),
        }
    }
}