matdoesdev/src/lib/blog.ts

import yaml from 'js-yaml'
import path from 'path'
import fs from 'fs'

export const postsDir = 'src/posts' as const

interface BlogPost {
	title: string
	body: string
	slug: string
}

/** Checks whether a slug is valid or not */
async function doesBlogPostExist(slug: string) {
	const existingPosts: string[] = await fs.promises.readdir(postsDir)

	return existingPosts.includes(slug)
}

/** Checks whether an asset exists in a blog post */
export async function doesAssetExist(postSlug: string, assetName: string): Promise<boolean> {
	// return false if the blog post doesn't exist
	if (!(await doesBlogPostExist(postSlug))) return false

	const existingAssets: string[] = await fs.promises.readdir(path.join(postsDir, postSlug))

	return existingAssets.includes(assetName)
}

/** Get a blog post by the slug, returning null if it doesn't exist */
export async function getPost(slug: string): Promise<BlogPost | null> {
	if (!doesBlogPostExist(slug)) return null

	// ok the post exists, so we can safely read the md file
	const postMarkdown = (
		await fs.promises.readFile(path.join(postsDir, slug, 'index.md'), 'utf8')
	).replace(/\r\n/g, '\n')

	const [_, yamlMetadata = null, markdownContent = null] =
		postMarkdown.match(/^---\n([\w\W]+?)\n---\n([\w\W]+)$/) ?? []

	if (yamlMetadata === null) throw new Error(`Blog post "${slug}" has no metadata.`)
	if (markdownContent === null) throw new Error(`Blog post "${slug}" has no content.`)

	const metadata: NonNullable<any> = yaml.load(yamlMetadata)

	// make sure the post has all the required metadata
	const requiredFields = ['title']
	for (const requiredField of requiredFields)
		if (!(requiredField in metadata))
			throw new Error(`Blog post "${slug}" is missing metadata field "${requiredField}"`)

	return {
		body: markdownContent.trim(),
		title: metadata.title,
		slug,
	}
}