import fs from 'fs/promises'
import path from 'path'
import matter from 'gray-matter'
import { compileMDX } from 'next-mdx-remote/rsc'
import { cache } from 'react'
import { useMDXComponents } from '@/mdx-components'
import remarkMath from 'remark-math'
import remarkGfm from 'remark-gfm'
import rehypeKatex from 'rehype-katex'
import rehypePrettyCode from 'rehype-pretty-code'

const postsDirectory = path.join(process.cwd(), 'content/posts')

export interface PostMeta {
  slug: string
  title: string
  date: string
  excerpt: string
}

export interface Post extends PostMeta {
  source: string
}

const getMdxFiles = cache(async () => {
  try {
    const files = await fs.readdir(postsDirectory)
    return files.filter((f) => f.endsWith('.mdx') || f.endsWith('.md'))
  } catch {
    return []
  }
})

export const getPosts = cache(async (): Promise<PostMeta[]> => {
  const files = await getMdxFiles()
  return Promise.all(
    files.map(async (file) => {
      const filePath = path.join(postsDirectory, file)
      const raw = await fs.readFile(filePath, 'utf8')
      const { data } = matter(raw)
      return {
        slug: file.replace(/\.(mdx|md)$/, ''),
        title: data.title ?? file,
        date: data.date ?? 'Unknown',
        excerpt: data.excerpt ?? '',
      } as PostMeta
    })
  ).then((posts) =>
    posts.sort((a, b) => new Date(b.date).getTime() - new Date(a.date).getTime())
  )
})

export const getPost = async (slug: string): Promise<Post | null> => {
  const files = await getMdxFiles()
  const file = files.find((f) => f.replace(/\.(mdx|md)$/, '') === slug)
  if (!file) return null

  const filePath = path.join(postsDirectory, file)
  const raw = await fs.readFile(filePath, 'utf8')
  const { data, content } = matter(raw)
  const components = useMDXComponents({})

  const { content: compiledContent } = await compileMDX({
    source: content,
    components,
    options: {
      parseFrontmatter: true,
      mdxOptions: {
        remarkPlugins: [remarkMath, remarkGfm],
        rehypePlugins: [
          [rehypePrettyCode, { theme: 'github-dark' }],
          rehypeKatex,
        ],
      },
    },
  })

  return {
    slug,
    title: data.title ?? file,
    date: data.date ?? 'Unknown',
    excerpt: data.excerpt ?? '',
    source: compiledContent,
  } as unknown as Post
}

export const getReadingTime = (content: string): number => {
  const words = content.replace(/<[^>]*>/g, '').trim().split(/\s+/).filter(Boolean).length
  return Math.max(1, Math.ceil(words / 200))
}