import knownNodes from './nodes/index.js'
import { useDocument } from '@terrace-lang/js'
import { createFileReader } from '@terrace-lang/js/readers/node-readline'

import process from 'node:process'
import path from 'node:path'

export default async function(filePath) {
  filePath = path.resolve(filePath)
  const doc = useDocument(createFileReader(filePath))
  const { next, line, match, tail, level, head } = doc

  const page = {
    type: `Page`,
    title: '',
    description: [],
    layout: '',
    headings: [],
    children: []
  }

  const context = {
    page,
    filePath
  }

  const originalCWD = process.cwd()
  while(await next()) {
    if (!line()) continue
    if (match('title')) page.title = tail()
    else if (match('layout')) page.layout = tail()
    else if (match('description')) {
      const l = level()
      while(await next(l)) {
        page.description.push(line(l))
      }
    }
    else if (match('Section')) {
      page.children.push(await knownNodes.Section(doc, level(), context))
    }
    else if (match('Include')) {
      page.children.push(await knownNodes.Include(doc, level(), context))
    }
  }
  process.chdir(originalCWD)

  // Structure headings into tree.
  page.headings.forEach((heading, index) => {
    let parent = null
    for (let i = index; i > 0; --i) {
      if (page.headings[i].level === heading.level - 1) {
        parent = page.headings[i]
        break
      }
    }

    if (parent) parent.children.push(heading)
  })

  page.headings = page.headings.filter(h => h.level === 2)

  return page
}