import { readFile } from 'node:fs/promises'
import { join } from 'node:path'

export default defineEventHandler(async (event) => {
  const slug = getRouterParam(event, 'slug')

  if (!slug || !/^[a-z0-9-]+$/.test(slug)) {
    throw createError({ statusCode: 400, statusMessage: 'Invalid slug' })
  }

  const filePath = join(process.cwd(), 'content', 'book', `${slug}.md`)

  try {
    const raw = await readFile(filePath, 'utf-8')
    const fmMatch = raw.match(/^---\n([\s\S]*?)\n---\n?/)

    let frontmatter = ''
    let body = raw

    if (fmMatch) {
      frontmatter = fmMatch[1]
      body = raw.slice(fmMatch[0].length)
    }

    return { slug, frontmatter, body }
  }
  catch {
    throw createError({ statusCode: 404, statusMessage: `Chapter "${slug}" not found` })
  }
})