// Serialize the constrained contenteditable composer DOM to the contact
// message Markdown subset (emphasis, links, lists, code, /_f/ images and
// file chips). The wire format is text: the server re-renders it with a
// strict, html-less MarkdownIt (pagerite/messages.py), so no user markup
// of any kind ever reaches a page. This serializer is for fidelity, not
// safety — anything it does not know is simply unwrapped.

const ESCAPE_RE = /([\\`*_[\]])/g

export function escapeMd(text) {
  return text.replace(ESCAPE_RE, '\\$1')
}

// Tags that open a new block at the composer's top level. Everything else
// there — text, B/I/A/SPAN formatting elements, inline images — is an
// inline run and joins the paragraph being accumulated: browsers happily
// put formatting directly under the editable root (a bolded segment of an
// undivided first line is a top-level <b>), and treating those as blocks
// would split the paragraph and drop the formatting.
const BLOCK_TAGS = new Set([
  'DIV', 'P', 'UL', 'OL', 'BLOCKQUOTE', 'PRE',
  'H1', 'H2', 'H3', 'H4', 'H5', 'H6', 'HR', 'TABLE',
])

// One message's Markdown from the composer root: inline runs become
// paragraphs, block elements become their own blocks, blank lines between.
export function serializeRich(root) {
  const blocks = []
  let run = []
  const flush = () => {
    const text = run.join('').trim()
    run = []
    if (text) blocks.push(text)
  }
  for (const node of root.childNodes) {
    if (node.nodeType === Node.ELEMENT_NODE && BLOCK_TAGS.has(node.tagName)) {
      flush()
      block(node, blocks)
    } else {
      run.push(inline(node))
    }
  }
  flush()
  return blocks.join('\n\n').replace(/\n{3,}/g, '\n\n').trim()
}

function block(node, out) {
  switch (node.tagName) {
    case 'UL':
      out.push([...node.children].map((li) => `- ${inlineChildren(li).trim()}`).join('\n'))
      break
    case 'OL':
      out.push([...node.children].map((li, i) => `${i + 1}. ${inlineChildren(li).trim()}`).join('\n'))
      break
    case 'BLOCKQUOTE':
      out.push(inlineChildren(node).split('\n').map((l) => `> ${l}`).join('\n'))
      break
    case 'PRE':
      out.push('```\n' + node.textContent + '\n```')
      break
    case 'HR':
      break
    default: {
      // DIV, P, headings: a paragraph of inline content.
      const text = inlineChildren(node).trim()
      if (text) out.push(text)
    }
  }
}

function inlineChildren(node) {
  return [...node.childNodes].map(inline).join('')
}

function inline(node) {
  if (node.nodeType === Node.TEXT_NODE) return escapeMd(node.textContent)
  if (node.nodeType !== Node.ELEMENT_NODE) return ''
  switch (node.tagName) {
    case 'B':
    case 'STRONG':
      return `**${inlineChildren(node)}**`
    case 'I':
    case 'EM':
      return `*${inlineChildren(node)}*`
    case 'CODE':
      return '`' + node.textContent.replace(/\\/g, '\\\\').replace(/`/g, '\\`') + '`'
    case 'BR':
      return '\n'
    case 'A': {
      const text = inlineChildren(node)
      const href = node.getAttribute('href') || ''
      return /^(https?:\/\/|mailto:|\/)/.test(href) ? `[${text}](${href})` : text
    }
    case 'IMG':
      // Uploaded image (data-path set by the composer on insert).
      return node.dataset.path ? `![${escapeMd(node.alt || 'image')}](${node.dataset.path})` : ''
    case 'SPAN':
      // Attachment chip (data-path + data-name); other spans unwrap.
      if (node.dataset.path && node.dataset.name) {
        return `[📎 ${escapeMd(node.dataset.name)}](${node.dataset.path})`
      }
      return wrapStyle(node, inlineChildren(node))
    default:
      return wrapStyle(node, inlineChildren(node))
  }
}

// Some browsers style formatting instead of tagging it (Firefox's
// execCommand produces <span style="font-weight: bold">): keep span-level
// bold/italic alive into the Markdown.
function wrapStyle(node, text) {
  if (!text.trim()) return text
  const s = node.style
  if (s) {
    if (/bold|bolder|[6-9]00/.test(s.fontWeight)) text = `**${text}**`
    if (s.fontStyle === 'italic' || s.fontStyle === 'oblique') text = `*${text}*`
  }
  return text
}