function esc(str) {
  return String(str)
    .replace(/&/g, '&')
    .replace(/</g, '&lt;')
    .replace(/>/g, '&gt;')
    .replace(/"/g, '&quot;')
}

export function nodeToHtml(node) {
  if (!node) return ''
  const ch = () => (node.content || []).map(nodeToHtml).join('')

  switch (node.type) {
    case 'doc':         return ch()
    case 'paragraph':   return `<p>${ch() || ' '}</p>\n`
    case 'heading': {
      const l = node.attrs?.level || 1
      return `<h${l}>${ch()}</h${l}>\n`
    }
    case 'text': {
      let t = esc(node.text || '')
      for (const m of (node.marks || [])) {
        if (m.type === 'bold')      t = `<strong>${t}</strong>`
        if (m.type === 'italic')    t = `<em>${t}</em>`
        if (m.type === 'underline') t = `<u>${t}</u>`
      }
      return t
    }
    case 'image': {
      const { src = '', alt = '', width = '100%', align = 'center' } = node.attrs || {}
      const ml = align === 'left' ? '0' : 'auto'
      const mr = align === 'right' ? '0' : 'auto'
      return `<img src="${esc(src)}" alt="${esc(alt)}" style="width:${esc(width)};display:block;margin-left:${ml};margin-right:${mr}"/>\n`
    }
    case 'bulletList':  return `<ul>\n${ch()}</ul>\n`
    case 'orderedList': return `<ol>\n${ch()}</ol>\n`
    case 'listItem':    return `<li>${ch()}</li>\n`
    case 'blockquote':  return `<blockquote>\n${ch()}</blockquote>\n`
    case 'hardBreak':   return '<br/>'
    default:            return ch()
  }
}

export function extractChapters(doc) {
  const chapters = []
  for (const node of (doc?.content || [])) {
    if (node.type === 'heading' && node.attrs?.level === 1) {
      chapters.push((node.content || []).map(n => n.text || '').join('') || 'Chapter')
    }
  }
  return chapters
}

// Splits the document into chapter sections at each H1 boundary
export function splitByChapters(doc, fallbackTitle = 'Story') {
  const nodes = doc?.content || []
  if (!nodes.length) return [{ title: fallbackTitle, html: '' }]

  const groups = []
  let current = { title: null, nodes: [] }

  for (const node of nodes) {
    if (node.type === 'heading' && node.attrs?.level === 1) {
      if (current.nodes.length > 0 || current.title !== null) {
        groups.push({ title: current.title || fallbackTitle, html: current.nodes.map(nodeToHtml).join('') })
      }
      current = {
        title: (node.content || []).map(n => n.text || '').join('') || 'Chapter',
        nodes: [node],
      }
    } else {
      current.nodes.push(node)
    }
  }
  if (current.nodes.length > 0 || current.title !== null) {
    groups.push({ title: current.title || fallbackTitle, html: current.nodes.map(nodeToHtml).join('') })
  }

  return groups.length ? groups : [{ title: fallbackTitle, html: nodes.map(nodeToHtml).join('') }]
}