server/md.js

// Markdown <-> ProseMirror JSON helpers. Deliberately minimal: paragraphs,
// headings 1-3, bullet/ordered lists (flat), code blocks, blockquotes,
// horizontal rules, $-delimited math; inline bold/italic/code/strike/links.

// --- ProseMirror JSON -> markdown ---

export function pmToMarkdown(pmDoc) {
  return (pmDoc.content || []).map(blockToMarkdown).filter(s => s !== null).join('\n\n')
}

export function blockToMarkdown(node) {
  switch (node.type) {
    case 'paragraph':
      return inlineToMarkdown(node.content)
    case 'heading':
      return '#'.repeat(node.attrs?.level || 1) + ' ' + inlineToMarkdown(node.content)
    case 'bulletList':
      return (node.content || []).map(li => '- ' + listItemText(li)).join('\n')
    case 'orderedList':
      return (node.content || []).map((li, i) => `${i + 1}. ` + listItemText(li)).join('\n')
    case 'taskList':
      return (node.content || []).map(li => `- [${li.attrs?.checked ? 'x' : ' '}] ` + listItemText(li)).join('\n')
    case 'table':
      return tableToMarkdown(node)
    case 'codeBlock':
      return '```' + (node.attrs?.language || '') + '\n' + textOf(node) + '\n```'
    case 'htmlBlock':
      return '```html-embed\n' + (node.attrs?.html || '') + '\n```'
    case 'blockquote':
      return (node.content || []).map(blockToMarkdown).join('\n\n').split('\n').map(l => '> ' + l).join('\n')
    case 'mathBlock':
      // canonical fenced form; the single-line `$$x$$` spelling also parses
      return '$$\n' + (node.attrs?.latex || '').trim() + '\n$$'
    case 'horizontalRule':
      return '---'
    case 'image':
      return `![${node.attrs?.alt || ''}](${node.attrs?.src || ''})`
    default:
      return textOf(node) || null
  }
}

function listItemText(li) {
  return (li.content || []).map(blockToMarkdown).join(' ')
}

function cellText(cell) {
  return (cell.content || [])
    .map(b => inlineToMarkdown(b.content))
    .join(' ')
    .replace(/\|/g, '\\|')
    .trim()
}

function tableToMarkdown(node) {
  const rows = (node.content || []).map(r => (r.content || []).map(cellText))
  if (!rows.length) return ''
  const cols = Math.max(...rows.map(r => r.length))
  const pad = r => {
    const c = r.slice()
    while (c.length < cols) c.push('')
    return c
  }
  const line = cells => '| ' + pad(cells).join(' | ') + ' |'
  // first row is the header (GFM requires one); a delimiter row follows it
  const out = [line(rows[0]), '| ' + Array(cols).fill('---').join(' | ') + ' |']
  for (const r of rows.slice(1)) out.push(line(r))
  return out.join('\n')
}

function textOf(node) {
  if (node.text) return node.text
  return (node.content || []).map(textOf).join('')
}

function inlineToMarkdown(content) {
  if (!content) return ''
  return content.map(n => {
    if (n.type === 'hardBreak') return '  \n'
    // an inline atom: its markdown IS its source, and it carries no marks
    if (n.type === 'mathInline') return '$' + (n.attrs?.latex || '') + '$'
    let text = n.text || ''
    // Nesting order is not free: a code span's body is literal, so `code` has to
    // wrap innermost or `**bold**` inside it would serialize to visible asterisks
    // (`` `**t**` ``). A link wraps outermost. ProseMirror stores marks in schema
    // order, so sort rather than trusting the array's order.
    const NESTING = ['code', 'bold', 'italic', 'strike', 'link']
    const marks = [...(n.marks || [])].sort((a, b) => NESTING.indexOf(a.type) - NESTING.indexOf(b.type))
    for (const mark of marks) {
      if (mark.type === 'bold') text = `**${text}**`
      else if (mark.type === 'italic') text = `*${text}*`
      else if (mark.type === 'code') text = '`' + text + '`'
      else if (mark.type === 'strike') text = `~~${text}~~`
      else if (mark.type === 'link') text = `[${text}](${mark.attrs?.href || ''})`
    }
    return text
  }).join('')
}

// --- markdown -> block descriptors ---
// Each descriptor: { type, attrs?, inline? (segments), items? (arrays of segments), text? }

export function markdownToBlocks(md) {
  const blocks = []
  const lines = (md || '').replace(/\r\n/g, '\n').split('\n')
  let i = 0
  while (i < lines.length) {
    const line = lines[i]
    if (!line.trim()) { i++; continue }

    const fence = line.match(/^```([\w-]*)\s*$/)
    if (fence) {
      const body = []
      i++
      while (i < lines.length && !/^```\s*$/.test(lines[i])) { body.push(lines[i]); i++ }
      i++
      // ```html-embed fences carry a live (sandboxed) HTML snippet, not code
      if (fence[1] === 'html-embed') blocks.push({ type: 'htmlBlock', text: body.join('\n') })
      else blocks.push({ type: 'codeBlock', attrs: fence[1] ? { language: fence[1] } : {}, text: body.join('\n') })
      continue
    }
    if (/^(---|\*\*\*)\s*$/.test(line.trim())) { blocks.push({ type: 'horizontalRule' }); i++; continue }

    // display math: `$$ ... $$` on one line, or fenced over several
    if (line.trim().startsWith('$$')) {
      const oneLine = line.trim().match(/^\$\$(.+)\$\$$/)
      if (oneLine) {
        blocks.push({ type: 'mathBlock', attrs: { latex: oneLine[1].trim() } })
        i++
        continue
      }
      const body = []
      i++
      while (i < lines.length && !lines[i].trim().endsWith('$$')) { body.push(lines[i]); i++ }
      if (i < lines.length) {
        // the closing line may carry the last of the formula: `... \end{aligned}$$`
        const tail = lines[i].trim().replace(/\$\$$/, '')
        if (tail) body.push(tail)
        i++
      }
      blocks.push({ type: 'mathBlock', attrs: { latex: body.join('\n').trim() } })
      continue
    }

    const image = line.match(/^!\[([^\]]*)\]\(([^)\s]+)\)\s*$/)
    if (image) {
      blocks.push({ type: 'image', attrs: { alt: image[1] || null, src: image[2] } })
      i++
      continue
    }

    const heading = line.match(/^(#{1,6})\s+(.*)$/)
    if (heading) {
      blocks.push({ type: 'heading', attrs: { level: Math.min(heading[1].length, 3) }, inline: tokenizeInline(heading[2]) })
      i++
      continue
    }

    // task list: "- [ ] text" / "- [x] text" (checked before plain bullets)
    if (/^\s*[-*]\s+\[[ xX]\]\s+/.test(line)) {
      const items = []
      while (i < lines.length && /^\s*[-*]\s+\[[ xX]\]\s+/.test(lines[i])) {
        const m = lines[i].match(/^\s*[-*]\s+\[([ xX])\]\s+(.*)$/)
        items.push({ checked: m[1].toLowerCase() === 'x', inline: tokenizeInline(m[2]) })
        i++
      }
      blocks.push({ type: 'taskList', items })
      continue
    }

    if (/^\s*[-*]\s+/.test(line)) {
      const items = []
      while (i < lines.length && /^\s*[-*]\s+/.test(lines[i]) && !/^\s*[-*]\s+\[[ xX]\]\s+/.test(lines[i])) {
        items.push(tokenizeInline(lines[i].replace(/^\s*[-*]\s+/, '')))
        i++
      }
      blocks.push({ type: 'bulletList', items })
      continue
    }

    // GFM table: a "| ... |" row immediately followed by a delimiter row
    if (line.includes('|') && i + 1 < lines.length && /^\s*\|?[\s:|-]*-[\s:|-]*\|?\s*$/.test(lines[i + 1]) && lines[i + 1].includes('-')) {
      const splitCells = l =>
        l
          .trim()
          .replace(/^\||\|$/g, '')
          .split(/(?<!\\)\|/)
          .map(c => c.replace(/\\\|/g, '|').trim())
      const rows = [splitCells(line)]
      i += 2 // header + delimiter
      while (i < lines.length && lines[i].includes('|') && lines[i].trim()) {
        rows.push(splitCells(lines[i]))
        i++
      }
      blocks.push({ type: 'table', rows: rows.map(cells => cells.map(tokenizeInline)) })
      continue
    }

    if (/^\s*\d+[.)]\s+/.test(line)) {
      const items = []
      while (i < lines.length && /^\s*\d+[.)]\s+/.test(lines[i])) {
        items.push(tokenizeInline(lines[i].replace(/^\s*\d+[.)]\s+/, '')))
        i++
      }
      blocks.push({ type: 'orderedList', items })
      continue
    }

    if (/^>\s?/.test(line)) {
      const body = []
      while (i < lines.length && /^>\s?/.test(lines[i])) {
        body.push(lines[i].replace(/^>\s?/, ''))
        i++
      }
      blocks.push({ type: 'blockquote', inline: tokenizeInline(body.join(' ')) })
      continue
    }

    // paragraph: consume until blank line or block marker
    const body = []
    while (i < lines.length && lines[i].trim() && !/^(#{1,6}\s|```|\$\$|\s*[-*]\s|\s*\d+[.)]\s|>\s?|---\s*$)/.test(lines[i])) {
      body.push(lines[i])
      i++
    }
    blocks.push({ type: 'paragraph', inline: tokenizeInline(body.join(' ')) })
  }
  return blocks
}

// --- inline tokenizer: returns [{ text, attrs }] where attrs maps mark name -> attrs object ---

// Emphasis: `_`/`__` do NOT open/close inside a word, so an underscore flanked
// by alphanumerics (e.g. `icm2026_schedule.html`) is literal — the boundary
// lookarounds gate the delimiters and let the span's body span such underscores
// (body is `.+?`, not `[^_]+`). Without this, `_..._` emphasis containing a
// filename underscore never matched and rendered as plain text.
//
// Every body is a lazy `[\s\S]+?` rather than a "no delimiter inside" run,
// because inline marks NEST: the body is handed back to tokenizeInline below.
// A `[^*]+` body could not hold `**bold with *italic* inside**` at all, and the
// single-`*` rule would then match the wrong pair of stars and mangle it.
//
// Rules are tried in order and the leftmost match wins, so `**` is listed
// before `*` and math before all emphasis. `*` also guards both delimiters with
// (?<!\*)/(?!\*) so a single-star span never opens or closes on half of a `**`.
const INLINE_RULES = [
  // literal: a code span's body is text by definition — `**` inside it is not bold
  { re: /`([^`]+)`/, attrs: () => ({ code: {} }), literal: true },
  { re: /\[([^\]]+)\]\(([^)\s]+)\)/, attrs: m => ({ link: { href: m[2] } }) },
  // `***x***` is bold+italic, and it needs its own rule ahead of `**`: given a
  // run of three stars the `**` rule would close on the wrong pair and leave a
  // stray `*` behind (`***t***` -> bold("*t") + "*").
  { re: /\*\*\*(?=\S)([\s\S]+?)(?<=\S)\*\*\*/, attrs: () => ({ bold: {}, italic: {} }) },
  { re: /(?<![A-Za-z0-9])___(?=\S)([\s\S]+?)(?<=\S)___(?![A-Za-z0-9])/, attrs: () => ({ bold: {}, italic: {} }) },
  { re: /\*\*(?=\S)([\s\S]+?)(?<=\S)\*\*/, attrs: () => ({ bold: {} }) },
  { re: /(?<![A-Za-z0-9])__(?=\S)([\s\S]+?)(?<=\S)__(?![A-Za-z0-9])/, attrs: () => ({ bold: {} }) },
  { re: /~~(?=\S)([\s\S]+?)(?<=\S)~~/, attrs: () => ({ strike: {} }) },
  { re: /(?<!\*)\*(?!\*)(?=\S)([\s\S]+?)(?<=\S)(?<!\*)\*(?!\*)/, attrs: () => ({ italic: {} }) },
  { re: /(?<![A-Za-z0-9])_(?=\S)(?!_)([\s\S]+?)(?<=\S)_(?![A-Za-z0-9])/, attrs: () => ({ italic: {} }) },
]

// Inline math, `$...$`. Matched BEFORE any emphasis so a formula's `*`, `_`,
// backticks and brackets cannot be eaten as markdown — `$\{x\}_{i}$ and
// $\{y\}_{j}$` used to turn into italics spanning both formulas.
//
// The delimiters are deliberately strict, because `$` is also money: no space
// just inside either delimiter (so "costs $5 and $10 more" is left alone), no
// newline, and never adjacent to a second `$` (so a `$$...$$` display block is
// not chewed into inline math from its second character).
const MATH_RE = /(?<!\$)\$(?![\s$])([^$\n]*[^\s$])\$(?!\$)/

// A math segment carries BOTH its source text and its latex: every consumer
// that only reads `.text` (diffing, signatures, plain-text descriptions) then
// sees `$x^2$` and behaves correctly, and only the few places that build real
// nodes — ProseMirror JSON, Yjs XML, preview HTML — look at `.math`.
function mathSegment(latex) {
  return { text: '$' + latex + '$', attrs: {}, math: latex }
}

export function tokenizeInline(text) {
  const segments = []
  let rest = text
  while (rest) {
    const math = rest.match(MATH_RE)
    // leftmost match wins; math ties break in math's favour so `$a * b$` stays math
    let best = math ? { index: math.index, m: math, math: true } : null
    for (const rule of INLINE_RULES) {
      const m = rest.match(rule.re)
      if (m && (!best || m.index < best.index)) best = { index: m.index, m, rule }
    }
    if (!best) { segments.push({ text: rest, attrs: {} }); break }
    if (best.index > 0) segments.push({ text: rest.slice(0, best.index), attrs: {} })
    if (best.math) {
      segments.push(mathSegment(best.m[1]))
    } else if (best.rule.literal) {
      segments.push({ text: best.m[1], attrs: best.rule.attrs(best.m) })
    } else {
      // marks nest: tokenize the body and fold this mark into each child, so
      // `**a `c` [l](u) $x$**` keeps its code span, link and formula
      const attrs = best.rule.attrs(best.m)
      for (const child of tokenizeInline(best.m[1])) segments.push({ ...child, attrs: { ...attrs, ...child.attrs } })
    }
    rest = rest.slice(best.index + best.m[0].length)
  }
  return segments.filter(s => s.text)
}