/**
 * Convert repo docs/ tree (.md files, recursive) into man(7) page objects (same pipeline as handbook).
 */
import { readFile, readdir } from 'fs/promises'
import { join, relative } from 'path'

import { handbookMdToDescription } from './ingest-handbook-for-man.mjs'

const SECTION = 7

function firstHeadingTitle(md) {
  const m = md.match(/^#\s+(.+)$/m)
  if (!m) return 'Bare OS documentation'
  let t = m[1]
  t = t.replace(/\*\*([^*]+)\*\*/g, '$1')
  t = t.replace(/`([^`]+)`/g, '$1')
  return t.trim()
}

/**
 * @param {string} absDir
 * @param {string} baseAbs
 * @returns {Promise<string[]>}
 */
async function collectMdRelPaths(absDir, baseAbs) {
  /** @type {string[]} */
  const out = []
  const ents = await readdir(absDir, { withFileTypes: true })
  ents.sort((a, b) => a.name.localeCompare(b.name))
  for (const ent of ents) {
    const full = join(absDir, ent.name)
    if (ent.isDirectory()) {
      out.push(...(await collectMdRelPaths(full, baseAbs)))
    } else if (ent.isFile() && ent.name.endsWith('.md')) {
      out.push(relative(baseAbs, full).replace(/\\/g, '/'))
    }
  }
  return out
}

/**
 * @param {string} relPosix path under docs/, e.g. reference/foo.md
 */
function relPathToManMeta(relPosix) {
  if (relPosix === 'README.md') {
    return {
      rel: relPosix,
      name: 'bare-os-docs',
      title:
        'Bare OS documentation (docs/) — hub, maps, and where to read next',
      aliases: ['docs', 'documentation', 'bare-os-documentation']
    }
  }
  const base = relPosix.replace(/\.md$/i, '')
  const slug = base.split('/').map((s) => s.toLowerCase()).join('-')
  return {
    rel: relPosix,
    name: 'docs-' + slug,
    title: '',
    aliases: []
  }
}

/**
 * @param {string} repoRoot
 * @returns {Promise<object[]>}
 */
export async function buildDocsManPages(repoRoot) {
  const docsDir = join(repoRoot, 'docs')
  let relPaths
  try {
    relPaths = await collectMdRelPaths(docsDir, docsDir)
  } catch {
    return []
  }

  relPaths.sort((a, b) => a.localeCompare(b))

  /** @type {{ rel: string, name: string, title: string, aliases?: string[] }[]} */
  const meta = relPaths.map(relPathToManMeta)
  const seen = new Set()
  for (const m of meta) {
    if (seen.has(m.name))
      throw new Error(`ingest-docs-for-man: duplicate man name "${m.name}"`)
    seen.add(m.name)
  }

  const pages = []
  for (let j = 0; j < meta.length; j++) {
    const m = meta[j]
    const filePath = join(docsDir, m.rel)
    const md = await readFile(filePath, 'utf8')
    const title = m.title || firstHeadingTitle(md)
    const description = handbookMdToDescription(md, 'docs/' + m.rel)
    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 })
    seeAlso.push({ name: 'bare-os-handbook', section: SECTION })

    const kw = new Set([
      'docs',
      'documentation',
      'bare-os',
      'reference',
      'markdown'
    ])
    for (const t of m.name.split(/[^a-z0-9]+/i)) {
      if (t.length > 1) kw.add(t.toLowerCase())
    }
    for (const seg of m.rel.replace(/\.md$/i, '').split(/[/\\]+/)) {
      for (const t of seg.toLowerCase().split(/[^a-z0-9]+/)) {
        if (t.length > 2) kw.add(t)
      }
    }
    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,
        'Documentation page (plain text from docs/' + m.rel + ')'
      ],
      description,
      descriptionMode: 'preserve',
      options: [],
      keywords: Array.from(kw),
      seeAlso,
      bareOsNotes:
        'Generated at build time from docs/' +
        m.rel +
        '. Mermaid diagrams omitted in terminal; see repo Markdown for figures.'
    }
    if (m.aliases && m.aliases.length) page.aliases = m.aliases
    pages.push(page)
  }

  return pages
}