organic/src/parser/text.rs

use nom::branch::alt;
/*

hypothetical link:
fn link = many_till(text_element, link_end)

but what if you start a bold?
fn bold = many_till(text_element, bold_end) could eat the link_end

Do I pass along break-conditions? Passing link_end into bold's parser?

I'll try a very simple language first where asterisks always start/end bold and links are just between [ and ]. Paragraphs will have a blank line between them.

*/
use nom::bytes::complete::tag;
use nom::character::complete::alphanumeric1;
use nom::character::complete::line_ending;
use nom::character::complete::space1;
use nom::combinator::eof;
use nom::combinator::map;
use nom::combinator::recognize;
use nom::error::VerboseError;
use nom::multi::many1;
use nom::multi::many_till;
use nom::sequence::tuple;
use nom::IResult;

use super::error::CustomError;

pub type Res<T, U> = IResult<T, U, CustomError<T>>;

#[derive(Debug)]
pub enum TextElement<'a> {
    Span(Span<'a>),
    Space(Space<'a>),
    LineBreak(LineBreak<'a>),
    Symbol(Symbol<'a>),
    Bold(Bold<'a>),
    Link(Link<'a>),
}

#[derive(Debug)]
pub struct Span<'a> {
    contents: &'a str,
}

#[derive(Debug)]
pub struct Space<'a> {
    contents: &'a str,
}

#[derive(Debug)]
pub struct LineBreak<'a> {
    contents: &'a str,
}

#[derive(Debug)]
pub struct Symbol<'a> {
    contents: &'a str,
}

#[derive(Debug)]
pub struct BlankLine<'a> {
    contents: &'a str,
}

#[derive(Debug)]
pub struct Sequence<'a> {
    pub contents: &'a str,
}

#[derive(Debug)]
pub struct Bold<'a> {
    pub contents: &'a str,
}

#[derive(Debug)]
pub struct Link<'a> {
    pub contents: &'a str,
}

pub fn line_break(input: &str) -> Res<&str, LineBreak> {
    map(line_ending, |s: &str| LineBreak { contents: s })(input)
}

pub fn space(input: &str) -> Res<&str, Space> {
    map(space1, |s: &str| Space { contents: s })(input)
}

pub fn span(input: &str) -> Res<&str, Span> {
    map(alphanumeric1, |s: &str| Span { contents: s })(input)
}

pub fn symbol(symbol_tag: &'static str) -> impl for<'a> Fn(&'a str) -> Res<&'a str, Symbol<'a>> {
    move |i: &str| map(tag(symbol_tag), |s: &str| Symbol { contents: s })(i)
}

/// A line containing only whitespace and then a line break
///
/// It is up to the caller to ensure this is called at the start of a line.
fn blank_line(input: &str) -> Res<&str, BlankLine> {
    map(
        recognize(many_till(
            map(space, TextElement::Space),
            map(line_break, TextElement::LineBreak),
        )),
        |contents| BlankLine { contents },
    )(input)
}

pub fn bold_start(input: &str) -> Res<&str, TextElement> {
    map(symbol("*"), TextElement::Symbol)(input)
}

pub fn bold_end(input: &str) -> Res<&str, TextElement> {
    map(symbol("*"), TextElement::Symbol)(input)
}

pub fn link_start(input: &str) -> Res<&str, TextElement> {
    map(symbol("["), TextElement::Symbol)(input)
}

pub fn link_end(input: &str) -> Res<&str, TextElement> {
    map(symbol("]"), TextElement::Symbol)(input)
}

pub fn paragraph_end(input: &str) -> Res<&str, &str> {
    alt((
        recognize(tuple((
            map(line_break, TextElement::LineBreak),
            many1(blank_line),
        ))),
        eof,
    ))(input)
}