path: root/src/subtokenize.rs

//! Deal with content in other content.
//!
//! To deal with content in content, *you* (a `micromark-rs` contributor) add
//! information on events.
//! Events are a flat list, but they can be connected to each other by setting
//! `previous` and `next` links.
//! These links:
//!
//! *   …must occur on [`Enter`][EventType::Enter] events only
//! *   …must occur on void events (they are followed by their corresponding
//!     [`Exit`][EventType::Exit] event)
//! *   …must have `content_type` field to define the kind of subcontent
//!
//! Links will then be passed through a tokenizer for the corresponding content
//! type by `subtokenize`.
//! The subevents they result in are split up into slots for each linked token
//! and replace those links.
//!
//! Subevents are not immediately subtokenized again because markdown prevents
//! us from doing so due to definitions, which can occur after references, and
//! thus the whole document needs to be parsed up to the level of definitions,
//! before any level that can include references can be parsed.

use crate::content::{string::start as string, text::start as text};
use crate::parser::ParseState;
use crate::tokenizer::{ContentType, Event, EventType, State, Tokenizer};
use crate::util::edit_map::EditMap;

/// Create a link between two [`Event`][]s.
///
/// Arbitrary (void) events can be linked together.
/// This optimizes for the common case where the token at `index` is connected
/// to the previous void token.
pub fn link(events: &mut [Event], index: usize) {
    link_to(events, index - 2, index);
}

/// Link two arbitrary [`Event`][]s together.
pub fn link_to(events: &mut [Event], pevious: usize, next: usize) {
    assert_eq!(events[pevious].event_type, EventType::Enter);
    assert_eq!(events[pevious + 1].event_type, EventType::Exit);
    assert_eq!(events[pevious + 1].token_type, events[pevious].token_type);
    assert_eq!(events[next].event_type, EventType::Enter);
    // Note: the exit of this event may not exist, so don’t check for that.

    let link_previous = events[pevious]
        .link
        .as_mut()
        .expect("expected `link` on previous");
    link_previous.next = Some(next);
    let link_next = events[next].link.as_mut().expect("expected `link` on next");
    link_next.previous = Some(pevious);

    assert_eq!(
        events[pevious].link.as_ref().unwrap().content_type,
        events[next].link.as_ref().unwrap().content_type
    );
}

/// Parse linked events.
///
/// Supposed to be called repeatedly, returns `1: true` when done.
pub fn subtokenize(events: &mut Vec<Event>, parse_state: &ParseState) -> bool {
    let mut map = EditMap::new();
    let mut done = true;
    let mut index = 0;

    while index < events.len() {
        let event = &events[index];

        // Find each first opening chunk.
        if let Some(ref link) = event.link {
            assert_eq!(event.event_type, EventType::Enter);

            // No need to enter linked events again.
            if link.previous == None {
                // Index into `events` pointing to a chunk.
                let mut link_index = Some(index);
                // Subtokenizer.
                let mut tokenizer = Tokenizer::new(event.point.clone(), parse_state);
                // Substate.
                let mut state = State::Fn(Box::new(if link.content_type == ContentType::String {
                    string
                } else {
                    text
                }));

                // Loop through links to pass them in order to the subtokenizer.
                while let Some(index) = link_index {
                    let enter = &events[index];
                    let link_curr = enter.link.as_ref().expect("expected link");
                    assert_eq!(enter.event_type, EventType::Enter);

                    if link_curr.previous != None {
                        tokenizer.define_skip(&enter.point);
                    }

                    state = tokenizer.push(
                        enter.point.index,
                        events[index + 1].point.index,
                        match state {
                            State::Fn(func) => func,
                            _ => unreachable!("cannot be ok/nok"),
                        },
                    );

                    link_index = link_curr.next;
                }

                tokenizer.flush(state, true);

                // Now, loop through all subevents to figure out which parts
                // belong where and fix deep links.
                let mut subindex = 0;
                let mut link_index = index;
                let mut slices = vec![];
                let mut slice_start = 0;

                while subindex < tokenizer.events.len() {
                    let subevent = &mut tokenizer.events[subindex];

                    // Find the first event that starts after the end we’re looking
                    // for.
                    if subevent.event_type == EventType::Enter
                        && subevent.point.index >= events[link_index + 1].point.index
                    {
                        slices.push((link_index, slice_start));
                        slice_start = subindex;
                        link_index = events[link_index].link.as_ref().unwrap().next.unwrap();
                    }

                    if subevent.link.is_some() {
                        // Need to call `subtokenize` again.
                        done = false;
                    }

                    // If there is a `next` link in the subevents, we have to change
                    // its index to account for the shifted events.
                    // If it points to a next event, we also change the next event’s
                    // reference back to *this* event.
                    if let Some(sublink_curr) = &mut subevent.link {
                        if let Some(next) = sublink_curr.next {
                            // The `index` in `events` where the current link is,
                            // minus 2 events (the enter and exit) for each removed
                            // link.
                            let shift = link_index - (slices.len() * 2);
                            sublink_curr.next = sublink_curr.next.map(|next| next + shift);
                            let next_ev = &mut tokenizer.events[next];
                            let sublink_next = next_ev.link.as_mut().unwrap();
                            sublink_next.previous =
                                sublink_next.previous.map(|previous| previous + shift);
                        }
                    }

                    subindex += 1;
                }

                slices.push((link_index, slice_start));

                // Finally, inject the subevents.
                let mut index = slices.len();

                while index > 0 {
                    index -= 1;
                    map.add(
                        slices[index].0,
                        2,
                        tokenizer.events.split_off(slices[index].1),
                    );
                }
            }
        }

        index += 1;
    }

    map.consume(events);

    done
}