'use strict'

const fs = require('fs')
const path = require('path')
const matter = require('gray-matter')

const grayMatterOptions = {
  lang: 'toml',
  delims: '+++'
}

function* lowercaseKeys (iterator) {
  for (let [k, v] of iterator) {
    yield [String(k).toLowerCase(), v]
  }
}

function canonicaliseMetadata (meta) {
  if (meta.data) {
    meta.data = new Map(lowercaseKeys(Object.entries(meta.data)))
  } else {
    meta.data = new Map()
  }
  return meta
}

function getTitle (file) {
  return path.basename(file.path, path.extname(file.path))
}

function get (filename) {
  const fileMatter = matter.read(filename, grayMatterOptions)
  fileMatter.basename = getTitle(fileMatter)
  return canonicaliseMetadata(fileMatter)
}

function getFolder (folder) {
  return new Map(
    fs
      .readdirSync(folder)
      .map(f => path.resolve(folder, f))
      .map(get)
      .map(f => [getTitle(f), f])
  )
}

function taxonomise (taxonomies, posts) {
  const taxons = new Map(Object.keys(taxonomies).map(t => [t, new Map()]))

  for (let [, post] of posts) {
    for (let [singularName, pluralName] of Object.entries(taxonomies)) {
      if (post.data.has(pluralName)) {
        for (let term of post.data.get(pluralName)) {
          const current = taxons.get(singularName).get(term)
          taxons
            .get(singularName)
            .set(term, current ? current.concat(post) : [post])
        }
      }
    }
  }

  return taxons
}

module.exports = function (config) {
  const posts = getFolder(config.folder)
  const taxonomies = taxonomise(config.taxonomies, posts)
  return {
    posts,
    taxonomies,
    get
  }
}