import { promises as fs } from 'fs'
import path from 'path'

import frontmatter from 'front-matter'

export interface PostMeta {
  slug: string,
  date: Date,
  title: string,
  subtitle?: string,
  unlisted: boolean,
  filePath: string,
  resources?: string[]
}

export interface Post extends Omit<PostMeta, "filePath"> {
  body: string,
}

type Attributes = { [key: string]: any }

const POST_FILE_PATTERN = /^(?<date>[0-9]{4}-[0-9]{2}-[0-9]{2}(-[0-9]{1,2})?)_(?<slug>[^\.]+)\.md$/

export async function getPostSlugs(): Promise<string[]> {
  const postsDir = path.join(process.cwd(), 'posts')
  const postPaths = await fs.readdir(postsDir)
  return postPaths.map(getSlugFromFilePath).filter(slug => slug !== null) as string[]
}

export function getSlugFromFilePath(postPath: string): string | null {
  const regexResult = POST_FILE_PATTERN.exec(postPath)
  if (!regexResult?.groups) return null
  return regexResult.groups.slug
}

export async function loadPageMetada(slug: string): Promise<PostMeta | null> {
  const postsDir = path.join(process.cwd(), 'posts')
  const postPaths = await fs.readdir(postsDir)
  const postMatch: RegExpExecArray | null | undefined = postPaths
    .map((postFile: string) => POST_FILE_PATTERN.exec(postFile))
    .filter((regexResult: RegExpExecArray | null) => regexResult !== null)
    .find((regexResult: RegExpExecArray) => regexResult.groups?.slug === slug)

  if (!postMatch) return null

  const fileName = `${postMatch.groups?.date}_${postMatch.groups?.slug}.md`
  const filePath = path.join(process.cwd(), 'posts', fileName)
  const fileContents = (await fs.readFile(filePath)).toString('utf8')
  const { attributes } = frontmatter(fileContents)
  const data: Attributes = attributes as Attributes

  if (!data.title) return null

  const [year, month, day] = postMatch.groups?.date.split('-') || []
  const date = new Date(Date.UTC(parseInt(year), parseInt(month) - 1, parseInt(day)))

  return {
    date,
    filePath,
    slug: postMatch.groups?.slug || '',
    title: data.title,
    subtitle: data.subtitle,
    unlisted: typeof data.unlisted === 'boolean' ? data.unlisted : false,
    resources: data.resources
  }
}

export async function loadSinglePage(slug: string): Promise<Post | null> {
  const postMeta = await loadPageMetada(slug)

  if (!postMeta) return null

  const fileContents = (await fs.readFile(postMeta.filePath)).toString('utf8')
  const { body } = frontmatter(fileContents)

  const { filePath, ...otherMeta } = postMeta

  return {
    ...otherMeta,
    body
  }
}