ron-parser 0.1.4

use nom::branch::alt;
use nom::bytes::streaming::{is_not, take_while_m_n};
use nom::character::streaming::{char, multispace1};
use nom::combinator::{map, map_opt, map_res, value, verify};
use nom::error::{FromExternalError, ParseError};
use nom::multi::fold_many0;
use nom::sequence::{delimited, preceded};
use nom::{IResult, Parser};

fn parse_unicode<'a, E>(input: &'a str) -> IResult<&'a str, char, E>
where
    E: ParseError<&'a str> + FromExternalError<&'a str, std::num::ParseIntError>,
{
    let parse_hex = take_while_m_n(1, 6, |c: char| c.is_ascii_hexdigit());

    let parse_delimited_hex = preceded(char('u'), delimited(char('{'), parse_hex, char('}')));

    let parse_u32 = map_res(parse_delimited_hex, move |hex| u32::from_str_radix(hex, 16));

    map_opt(parse_u32, std::char::from_u32).parse(input)
}

/// Parse an escaped character: \n, \t, \r, \u{00AC}, etc.
fn parse_escaped_char<'a, E>(input: &'a str) -> IResult<&'a str, char, E>
where
    E: ParseError<&'a str> + FromExternalError<&'a str, std::num::ParseIntError>,
{
    preceded(
        char('\\'),
        alt((
            parse_unicode,
            value('\n', char('n')),
            value('\r', char('r')),
            value('\t', char('t')),
            value('\u{08}', char('b')),
            value('\u{0C}', char('f')),
            value('\\', char('\\')),
            value('/', char('/')),
            value('"', char('"')),
        )),
    )
    .parse(input)
}

/// Parse a backslash, followed by any amount of whitespace. This is used later
/// to discard any escaped whitespace.
fn parse_escaped_whitespace<'a, E: ParseError<&'a str>>(
    input: &'a str,
) -> IResult<&'a str, &'a str, E> {
    preceded(char('\\'), multispace1).parse(input)
}

/// Parse a non-empty block of text that doesn't include \ or "
fn parse_literal<'a, E: ParseError<&'a str>>(input: &'a str) -> IResult<&'a str, &'a str, E> {
    let not_quote_slash = is_not("\"\\");

    verify(not_quote_slash, |s: &str| !s.is_empty()).parse(input)
}

/// A string fragment contains a fragment of a string being parsed: either
/// a non-empty Literal (a series of non-escaped characters), a single
/// parsed escaped character, or a block of escaped whitespace.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum StringFragment<'a> {
    Literal(&'a str),
    EscapedChar(char),
    EscapedWS,
}

/// Combine parse_literal, parse_escaped_whitespace, and parse_escaped_char
/// into a StringFragment.
fn parse_fragment<'a, E>(input: &'a str) -> IResult<&'a str, StringFragment<'a>, E>
where
    E: ParseError<&'a str> + FromExternalError<&'a str, std::num::ParseIntError>,
{
    alt((
        map(parse_literal, StringFragment::Literal),
        map(parse_escaped_char, StringFragment::EscapedChar),
        value(StringFragment::EscapedWS, parse_escaped_whitespace),
    ))
    .parse(input)
}

/// Parse a string. Use a loop of parse_fragment and push all of the fragments
/// into an output string.
pub fn parse_string<'a, E>(input: &'a str) -> IResult<&'a str, String, E>
where
    E: ParseError<&'a str> + FromExternalError<&'a str, std::num::ParseIntError>,
{
    let build_string = fold_many0(parse_fragment, String::new, |mut string, fragment| {
        match fragment {
            StringFragment::Literal(s) => string.push_str(s),
            StringFragment::EscapedChar(c) => string.push(c),
            StringFragment::EscapedWS => {}
        }
        string
    });

    delimited(char('"'), build_string, char('"')).parse(input)
}