opencrabs 0.3.41

//! Block-level markdown parsing: the top-level dispatcher that turns lines of
//! markdown into [`Block`]s, delegating tables to [`super::table`], lists to
//! [`super::list`], and inline content to [`super::inline`].

use super::ast::Block;
use super::inline::parse_inlines;
use super::{list, table};

/// Parse a markdown document into a block list.
pub(crate) fn parse_markdown(input: &str) -> Vec<Block> {
    let lines: Vec<String> = input.lines().map(str::to_string).collect();
    parse_blocks(&lines)
}

/// Parse a slice of lines into blocks. Used recursively for blockquote bodies
/// and list-item children.
pub(super) fn parse_blocks(lines: &[String]) -> Vec<Block> {
    let mut blocks = Vec::new();
    let mut i = 0;

    while i < lines.len() {
        let t = lines[i].trim();
        if t.is_empty() {
            i += 1;
            continue;
        }

        // Fenced code block.
        if is_fence(t) {
            let lang = fence_lang(t);
            i += 1;
            let mut buf = Vec::new();
            while i < lines.len() && !is_fence(lines[i].trim()) {
                buf.push(lines[i].clone());
                i += 1;
            }
            i += 1; // consume the closing fence (no-op past EOF)
            blocks.push(Block::Code {
                lang,
                text: buf.join("\n"),
            });
            continue;
        }

        // Pipe table (header row + separator row).
        if let Some((tbl, next)) = table::try_parse(lines, i) {
            blocks.push(Block::Table(tbl));
            i = next;
            continue;
        }

        // ATX heading.
        if let Some((level, content)) = heading(t) {
            blocks.push(Block::Heading {
                level,
                content: parse_inlines(content),
            });
            i += 1;
            continue;
        }

        // Horizontal rule.
        if is_divider(t) {
            blocks.push(Block::Divider);
            i += 1;
            continue;
        }

        // Block math: `$$` fence or a single `$$ ... $$` line.
        if t == "$$" {
            i += 1;
            let mut buf = Vec::new();
            while i < lines.len() && lines[i].trim() != "$$" {
                buf.push(lines[i].clone());
                i += 1;
            }
            i += 1; // consume the closing `$$`
            blocks.push(Block::Math(buf.join("\n")));
            continue;
        }
        if let Some(inner) = t.strip_prefix("$$").and_then(|s| s.strip_suffix("$$"))
            && !inner.is_empty()
        {
            blocks.push(Block::Math(inner.trim().to_string()));
            i += 1;
            continue;
        }

        // Blockquote.
        if t.starts_with('>') {
            let mut buf = Vec::new();
            while i < lines.len() && lines[i].trim_start().starts_with('>') {
                let l = lines[i].trim_start();
                let stripped = l.strip_prefix('>').unwrap_or(l);
                buf.push(stripped.strip_prefix(' ').unwrap_or(stripped).to_string());
                i += 1;
            }
            blocks.push(Block::Quote(parse_blocks(&buf)));
            continue;
        }

        // List.
        if list::is_item(&lines[i]) {
            blocks.push(Block::List(list::parse_list(lines, &mut i)));
            continue;
        }

        // Paragraph: gather soft-wrapped lines until a blank or a new block.
        let mut buf = Vec::new();
        while i < lines.len() {
            if lines[i].trim().is_empty() || starts_block(lines, i) {
                break;
            }
            buf.push(lines[i].trim().to_string());
            i += 1;
        }
        blocks.push(Block::Paragraph(parse_inlines(&buf.join(" "))));
    }

    blocks
}

/// Whether line `i` begins any block-level construct (used to terminate a
/// paragraph run).
fn starts_block(lines: &[String], i: usize) -> bool {
    let t = lines[i].trim();
    t.is_empty()
        || is_fence(t)
        || heading(t).is_some()
        || is_divider(t)
        || t.starts_with('>')
        || t == "$$"
        || list::is_item(&lines[i])
        || table::try_parse(lines, i).is_some()
}

/// A fence line: three or more backticks.
fn is_fence(t: &str) -> bool {
    t.starts_with("```")
}

/// The language tag of an opening fence, if any.
fn fence_lang(t: &str) -> Option<String> {
    let lang = t.trim_start_matches('`').trim();
    (!lang.is_empty()).then(|| lang.to_string())
}

/// Parse an ATX heading, returning `(level, content)`.
fn heading(t: &str) -> Option<(u8, &str)> {
    let hashes = t.chars().take_while(|&c| c == '#').count();
    if (1..=6).contains(&hashes) {
        let rest = &t[hashes..];
        if rest.is_empty() || rest.starts_with(' ') {
            return Some((hashes as u8, rest.trim()));
        }
    }
    None
}

/// Whether `t` is a horizontal rule (`---`, `***`, `___`, possibly spaced).
fn is_divider(t: &str) -> bool {
    let s: String = t.chars().filter(|c| !c.is_whitespace()).collect();
    s.len() >= 3
        && (s.bytes().all(|b| b == b'-')
            || s.bytes().all(|b| b == b'*')
            || s.bytes().all(|b| b == b'_'))
}