path: root/src/parse.rs

use crate::*;

pub fn parse(markdown: &str) -> Vec<Block> {
    let mut document = Vec::new();
    let lines: Vec<&str> = markdown.lines().map(|l| l.trim_start()).collect();
    let mut i = 0;

    // Gather all consecutive lines that begin with a given substring and run a
    // function over them. The function must be `fn(&[&str])->Result<Block,()>`.
    macro_rules! gather {
        ($prefix:expr, $func:ident) => {{
            let start = i;
            for line in &lines[i..] {
                if line.starts_with($prefix) {
                    i += 1;
                    continue;
                }
                break;
            }
            let gathered_lines = &lines[start..i];
            match gathered_lines.is_empty() {
                false => $func(gathered_lines),
                true => Err(()),
            }
        }};
    }

    loop {
        let line = match lines.get(i) {
            Some(line) => line,
            None => return document,
        };
        if line.is_empty() {
            i += 1;
            continue;
        } else if let Ok(heading) = parse_heading(line) {
            document.push(heading);
            i += 1;
        } else if let Ok(quote) = gather!(">", parse_quote) {
            document.push(quote);
        } else if let Ok(list) = gather!("- ", parse_list) {
            document.push(list);
        } else if let Ok(table) = gather!("|", parse_table) {
            document.push(table);
        } else if line.starts_with("```") {
            let language = line[3..].to_string();
            let mut code_lines = Vec::new();
            i += 1;
            for line in &lines[i..] {
                match line.trim() == "```" {
                    true => break,
                    false => {
                        code_lines.push(line.to_string());
                        i += 1
                    }
                }
            }
            document.push(Block::Code(language, code_lines));
            i += 1;
        } else {
            document.push(parse_paragraph(line));
            i += 1;
        };
    }
}

/// Returns the substring from `chars` that is between the `start` and `end`
/// delimiters. Returns None if `chars` does not start with `start`, or if an
/// occurance of `start` and `end` cannot be found within `chars`. There must
/// not be a space after the occurance of `start` or before the occurance of
/// `end`. If `start` and `end` consist of just one or more of the same
/// character, the content must contain at least one other character than
/// that one.
fn capture(chars: &[char], start: &str, end: &str) -> Option<String> {
    // Determine if `pattern` contains only a single unique character
    let single_char_in_pattern = match start.chars().next() {
        Some(first_char) => {
            let start_and_end = start.chars().chain(end.chars());
            start_and_end.fold(Some(first_char), |accum, elem| match accum {
                Some(c) if c == elem => accum,
                _ => None,
            })
        }
        None => None,
    };
    let is_space = |i: usize| chars.get(i) == Some(&' ');
    fn starts_with_pattern(chars: &[char], pattern: &str) -> bool {
        let mut i = 0;
        for ref c in pattern.chars() {
            match chars.get(i) {
                Some(v) if v == c => i += 1,
                _ => return false,
            }
        }
        true
    }
    if !starts_with_pattern(chars, start) {
        return None;
    }
    let text_start = start.len();
    if is_space(text_start) {
        return None;
    };
    let mut i = text_start;
    loop {
        i += 1;
        if chars.get(i).is_none() {
            return None;
        }
        if starts_with_pattern(&chars[i..], end) {
            if is_space(i - 1) {
                continue;
            }
            let text_content: String = chars[text_start..i].iter().collect();
            match single_char_in_pattern {
                None => return Some(text_content),
                Some(c) => {
                    if text_content.chars().any(|e| e != c) {
                        return Some(text_content);
                    }
                }
            };
        }
    }
}

fn parse_text(line: &str) -> Line {
    let mut block_content: Line = Vec::new();
    let chars: Vec<char> = line.chars().collect();
    let mut normal = String::new();
    let mut i = 0;

    macro_rules! commit_normal {
        () => {
            if !normal.is_empty() {
                let normal_text = Text::Normal(std::mem::take(&mut normal));
                block_content.push(normal_text);
            }
        };
    }
    let patterns: [(&str, &str, fn(String) -> Text); 7] = [
        ("***", "***", Text::BoldItalic),
        ("**", "**", Text::Bold),
        ("*", "*", Text::Italic),
        ("___", "___", Text::BoldItalic),
        ("__", "__", Text::Bold),
        ("_", "_", Text::Italic),
        ("`", "`", Text::Code),
    ];

    'outer: loop {
        // Check if a simple, non-Normal text type starts at this character
        for (start, end, text_type) in patterns.iter() {
            if let Some(string) = capture(&chars[i..], start, end) {
                i += string.len() + start.len() + end.len();
                commit_normal!();
                block_content.push(text_type(string));
                continue 'outer;
            }
        }
        // Check if a wiki-style hyperlink starts at this character
        if let Some(content) = capture(&chars[i..], "[[", "]]") {
            i += content.len() + 4;
            commit_normal!();
            block_content.push(Text::WikiLink(content));
            continue 'outer;
        }

        // Check if a long-form hyperlink starts at this character
        if let Some(label) = capture(&chars[i..], "[", "]") {
            let target_len = label.len() + 2;
            if let Some(target) = capture(&chars[i + target_len..], "(", ")") {
                i += target_len + target.len() + 2;
                commit_normal!();
                block_content.push(Text::Hyperlink(Hyperlink { label, target }))
            }
        }

        // No new text type started here, this must just be normal text
        match chars.get(i) {
            Some(c) => {
                normal.push(*c);
                i += 1;
            }
            None => {
                commit_normal!();
                break;
            }
        }
    }
    return block_content;
}

fn parse_heading(line: &str) -> Result<Block, ()> {
    let (heading_type, content): (fn(Line) -> Block, &str) = if line.starts_with("# ") {
        (Block::Heading1, &line[2..])
    } else if line.starts_with("## ") {
        (Block::Heading2, &line[3..])
    } else if line.starts_with("### ") {
        (Block::Heading3, &line[4..])
    } else {
        return Err(());
    };
    if content.is_empty() {
        return Err(());
    };
    Ok(heading_type(parse_text(content)))
}

/// Accepts a slice of lines that begin with '>'
fn parse_quote(lines: &[&str]) -> Result<Block, ()> {
    let mut content = Vec::new();
    for line in lines {
        content.push(if *line == ">" {
            Vec::new()
        } else {
            parse_text(&line[2..])
        });
    }
    Ok(Block::Quote(content))
}

fn parse_list(lines: &[&str]) -> Result<Block, ()> {
    Ok(Block::List(
        lines.iter().map(|l| parse_text(&l[2..])).collect(),
    ))
}

fn parse_paragraph(line: &str) -> Block {
    Block::Paragraph(parse_text(line))
}

fn parse_table(lines: &[&str]) -> Result<Block, ()> {
    if lines.len() < 3 {
        return Err(());
    }
    let names = split_columns(lines[0])?;
    let dividers = split_columns(lines[1])?;
    if names.len() != dividers.len() {
        return Err(());
    }
    let mut columns = Vec::new();
    for (name, divider) in std::iter::zip(names.iter(), dividers.iter()) {
        let alignment = Alignment::from_str(divider)?;
        columns.push(Column {
            name: parse_text(name),
            alignment,
        })
    }
    let mut rows = Vec::new();
    for row in &lines[2..] {
        let split_row: Vec<Line> = split_columns(row)?.iter().map(|s| parse_text(s)).collect();
        if split_row.len() != columns.len() {
            return Err(());
        }
        rows.push(split_row);
    }
    Ok(Block::Table(Table { columns, rows }))
}

fn split_columns(line: &str) -> Result<Vec<String>, ()> {
    // Find the index after the first |, and before the last |
    let mut start = None;
    let mut end = None;
    for (i, c) in line.chars().enumerate() {
        if c == '|' {
            if start.is_none() {
                start = Some(i + 1);
            } else {
                end = Some(i);
            }
        }
    }
    match (start, end) {
        (Some(s), Some(e)) => {
            let chars: Vec<char> = line.chars().collect();
            let string: String = chars[s..e].iter().collect();
            let split = string.split('|');
            Ok(split.map(|s| s.trim().to_string()).collect())
        }
        _ => Err(()),
    }
}