'use strict'

const fs = require('fs')
const path = require('path')
const matter = require('gray-matter')
const Markdown = require('markdown-it')

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

const markdownOptions = {
  html: true,
  typographer: true
}

const markdown = new Markdown(markdownOptions)

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 render (post) {
  return markdown.render(post.content)
}

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 toTags (posts) {
  const tags = new Map()
  for (let [, post] of posts) {
    if (post.data.has('tags')) {
      for (let tag of post.data.get('tags')) {
        tags.set(tag, (tags.get(tag) || []).concat([post]))
      }
    }
  }
  return tags
}

module.exports = {
  get,
  getFolder,
  toTags,
  render
}