public-blog/lib/posts.ts

import fs from 'fs'
import path from 'path'
import matter from 'gray-matter'
import { cache } from 'react'

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

export interface PostMeta {
  slug: string
  title: string
  date: string
  excerpt: string
  tags: string[]
  author: string | null
  coverImage: string | null
  readingTime: number
}

export type Post = PostMeta

export interface TagMeta {
  slug: string
  label: string
  count: number
}

const normalizeString = (value: unknown, fallback: string): string => {
  if (typeof value === 'string') return value
  if (value instanceof Date && !Number.isNaN(value.getTime())) return value.toISOString()
  if (typeof value === 'number' || typeof value === 'boolean') return String(value)
  return fallback
}

const normalizeOptionalString = (value: unknown): string | null => {
  if (typeof value !== 'string') return null

  const normalized = value.trim()
  return normalized.length > 0 ? normalized : null
}

const normalizeTags = (value: unknown): string[] => {
  const values = Array.isArray(value) ? value : typeof value === 'string' ? [value] : []

  return values
    .map((tag) => normalizeString(tag, '').trim())
    .filter((tag) => tag.length > 0)
}

export const normalizePostData = (
  slug: string,
  data: Record<string, unknown>,
  readingTime: number
): PostMeta => ({
  slug,
  title: normalizeString(data.title, slug),
  date: normalizeString(data.date, 'Unknown'),
  excerpt: normalizeString(data.excerpt, ''),
  tags: normalizeTags(data.tags),
  author: normalizeOptionalString(data.author),
  coverImage: normalizeOptionalString(data.coverImage),
  readingTime,
})

export const tagToSlug = (tag: string): string =>
  tag
    .normalize('NFKD')
    .toLowerCase()
    .replace(/[\u0300-\u036f]/g, '')
    .replace(/\+/g, ' plus ')
    .replace(/#/g, ' sharp ')
    .replace(/[\\/]+/g, ' ')
    .replace(/[^\p{L}\p{N}]+/gu, '-')
    .replace(/-{2,}/g, '-')
    .replace(/^-|-$/g, '')

const getMdxFiles = cache(async () => {
  try {
    const files = await fs.promises.readdir(postsDirectory)
    return files.filter((file) => file.endsWith('.mdx')).sort((a, b) => a.localeCompare(b))
  } 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.promises.readFile(filePath, 'utf-8')
      const { data, content } = matter(raw)
      const slug = file.replace(/\.mdx$/, '')
      const readingTime = getReadingTime(content)

      return normalizePostData(slug, data, readingTime)
    })
  ).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$/, '') === slug)
  if (!file) return null

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

  return normalizePostData(slug, data, getReadingTime(content)) satisfies 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))
}

export const getAllTags = cache(async (): Promise<TagMeta[]> => {
  const posts = await getPosts()
  const tags = new Map<string, TagMeta>()

  posts.forEach((post) => {
    const postTagSlugs = new Set<string>()

    post.tags.forEach((tag) => {
      const slug = tagToSlug(tag)
      if (!slug || postTagSlugs.has(slug)) return

      postTagSlugs.add(slug)
      const existing = tags.get(slug)

      if (existing) {
        existing.count += 1
        if (tag.localeCompare(existing.label) < 0) existing.label = tag
        return
      }

      tags.set(slug, { slug, label: tag, count: 1 })
    })
  })

  return Array.from(tags.values()).sort(
    (a, b) => a.label.localeCompare(b.label) || a.slug.localeCompare(b.slug)
  )
})

export const getPostsByTag = cache(async (tagSlug: string): Promise<PostMeta[]> => {
  const posts = await getPosts()
  const normalizedTagSlug = tagToSlug(tagSlug)

  return posts.filter((post) => post.tags.some((tag) => tagToSlug(tag) === normalizedTagSlug))
})