/**
 * Convert repo handbook/*.md into man(7) page objects merged at build time.
 */
import { readFile, readdir } from 'fs/promises'
import { join } from 'path'

const SECTION = 7

function stripMdInline(s) {
  let t = String(s)
  t = t.replace(/\[([^\]]*)\]\(([^)]+)\)/g, '$1 <$2>')
  t = t.replace(/\*\*([^*]+)\*\*/g, '$1')
  t = t.replace(/__([^_]+)__/g, '$1')
  t = t.replace(/\*([^*]+)\*/g, '$1')
  t = t.replace(/`([^`]+)`/g, '$1')
  return t.trim()
}

/**
 * @param {string} md
 * @param {string} sourceFile
 */
export function handbookMdToDescription(md, sourceFile) {
  const lines = md.split('\n')
  const out = []
  let i = 0
  let inFence = false
  /** @type {string} */
  let fenceKind = ''

  while (i < lines.length) {
    const line = lines[i]
    const fenceM = line.match(/^(\s*)```(\w*)\s*$/)
    if (fenceM) {
      if (!inFence) {
        inFence = true
        fenceKind = fenceM[2] || ''
        i++
        continue
      }
      inFence = false
      fenceKind = ''
      i++
      continue
    }
    if (inFence) {
      if (fenceKind === 'mermaid') {
        i++
        continue
      }
      out.push('    ' + line)
      i++
      continue
    }

    const t = line.trim()
    if (/^---+$/.test(t)) {
      out.push('')
      i++
      continue
    }

    const h = line.match(/^(#{1,6})\s+(.*)$/)
    if (h) {
      const text = stripMdInline(h[2])
      if (text) {
        out.push('')
        out.push(text.toUpperCase())
        out.push('')
      }
      i++
      continue
    }

    if (/^\s*[-*]\s+/.test(line)) {
      out.push(stripMdInline(line.replace(/^\s+/, '')))
      i++
      continue
    }

    if (/^\s*\d+\.\s+/.test(line)) {
      out.push(stripMdInline(line.trim()))
      i++
      continue
    }

    if (t.startsWith('|')) {
      if (/^\|[\s-:|]+\|$/.test(t)) {
        i++
        continue
      }
      out.push(stripMdInline(t))
      i++
      continue
    }

    if (!t) {
      out.push('')
      i++
      continue
    }

    out.push(stripMdInline(line.trim()))
    i++
  }

  let body = out
    .join('\n')
    .replace(/\n{3,}/g, '\n\n')
    .trim()
  if (!body) body = '(empty chapter — see ' + sourceFile + ' in the repo)'
  return body
}

function firstHeadingTitle(md) {
  const m = md.match(/^#\s+(.+)$/m)
  return m ? stripMdInline(m[1]) : 'Bare OS handbook'
}

/**
 * @param {string} repoRoot
 * @returns {Promise<object[]>}
 */
export async function buildHandbookManPages(repoRoot) {
  const handbookDir = join(repoRoot, 'handbook')
  let names
  try {
    names = (await readdir(handbookDir)).filter((f) => f.endsWith('.md'))
  } catch {
    return []
  }

  names.sort((a, b) => {
    if (a === 'README.md') return -1
    if (b === 'README.md') return 1
    return a.localeCompare(b)
  })

  /** @type {{ file: string, name: string, title: string, aliases?: string[] }[]} */
  const meta = []
  for (const file of names) {
    if (file === 'README.md') {
      meta.push({
        file,
        name: 'bare-os-handbook',
        title: 'Bare OS handbook — table of contents and reading order',
        aliases: ['handbook', 'bare-os-handbook-index']
      })
    } else {
      const base = file.replace(/\.md$/i, '')
      meta.push({
        file,
        name: 'handbook-' + base,
        title: '',
        aliases: []
      })
    }
  }

  const pages = []
  for (let j = 0; j < meta.length; j++) {
    const m = meta[j]
    const path = join(handbookDir, m.file)
    const md = await readFile(path, 'utf8')
    const title = m.title || firstHeadingTitle(md)
    const description = handbookMdToDescription(md, 'handbook/' + m.file)
    const next = meta[j + 1]
    const prev = meta[j - 1]
    /** @type {{ name: string, section: number }[]} */
    const seeAlso = []
    if (next) seeAlso.push({ name: next.name, section: SECTION })
    if (prev) seeAlso.push({ name: prev.name, section: SECTION })
    seeAlso.push({ name: 'man', section: 1 })

    const kw = new Set([
      'handbook',
      'bare-os',
      'documentation',
      'narrative',
      'chapter'
    ])
    for (const t of m.name.split(/[^a-z0-9]+/i)) {
      if (t.length > 1) kw.add(t.toLowerCase())
    }
    for (const t of title.toLowerCase().split(/[^a-z0-9]+/)) {
      if (t.length > 2) kw.add(t)
    }

    const page = {
      name: m.name,
      section: SECTION,
      title,
      synopsis: [
        'man 7 ' + m.name,
        'Handbook chapter (plain text from handbook/' + m.file + ')'
      ],
      description,
      descriptionMode: 'preserve',
      options: [],
      keywords: Array.from(kw),
      seeAlso,
      bareOsNotes:
        'Generated at build time from handbook/' +
        m.file +
        '. Diagrams in ```mermaid blocks are omitted; open the Markdown in the repo for figures.'
    }
    if (m.aliases && m.aliases.length) page.aliases = m.aliases
    pages.push(page)
  }

  return pages
}