website/src/lib/seo.ts

import { formatTitle, getTitle, type SiteEnvironment } from './title';

export const SITE_ORIGIN = 'https://stanrunge.dev';

type Article = {
	title: string;
	content: string;
	updatedAt: Date | string;
};
type List = { name: string; isProgress: boolean; items: { name: string }[] };
type Race = { short: string; distance: number; discipline: string };
type PageContent = { blogArticle?: Article; list?: List; race?: Race };

type Seo = {
	title: string;
	description: string;
	url: string;
	indexable: boolean;
	type: 'website' | 'article';
	image: string;
	imageAlt: string;
	modifiedAt?: string;
};

const publicPages: Record<string, { title: string; description: string }> = {
	'/': {
		title: 'Projects, lists and writing',
		description: 'Stan Runge’s projects, lists, writing and experience.'
	},
	'/projects': {
		title: 'Projects',
		description: 'Software projects by Stan Runge, including Catchemall, Animaldex and Derby Lens.'
	},
	'/blog': { title: 'Blog', description: 'Articles and notes by Stan Runge.' },
	'/lists': { title: 'Lists', description: 'Lists collected and maintained by Stan Runge.' },
	'/projects/catch-em-all': {
		title: 'Catchemall',
		description: 'Track which Pokémon you have caught across 53 games and 1,025 Pokémon.'
	},
	'/projects/animaldex': {
		title: 'Animaldex',
		description: 'Find and add neighborhood animals on a map.'
	},
	'/projects/derby': {
		title: 'Derby Lens',
		description: 'Estimate horse racing odds and compare them with market prices.'
	},
	'/projects/spotify-beatmap-finder': {
		title: 'osu! map finder',
		description: 'Find osu! beatmaps for Spotify songs, albums and playlists.'
	},
	'/projects/world-opinions': {
		title: 'World Opinions',
		description:
			'How political words, parties, values and national histories differ across the world.'
	}
};

function excerpt(markdown: string): string {
	return markdown
		.replace(/!\[[^\]]*\]\([^)]*\)/g, '')
		.replace(/\[([^\]]+)\]\([^)]*\)/g, '$1')
		.replace(/<[^>]*>/g, ' ')
		.replace(/[`*_>#~|]/g, ' ')
		.replace(/\s+/g, ' ')
		.trim()
		.slice(0, 160);
}

function date(value: Date | string): string | undefined {
	const parsed = new Date(value);
	return Number.isNaN(parsed.getTime()) ? undefined : parsed.toISOString();
}

export function getSeo(
	pathname: string,
	content: PageContent = {},
	environment: SiteEnvironment = null
): Seo {
	const path = pathname.replace(/\/$/, '') || '/';
	const url = new URL(path, SITE_ORIGIN).href;
	let page = publicPages[path];
	let type: Seo['type'] = 'website';
	let modifiedAt: string | undefined;

	if (/^\/blog\/[^/]+$/.test(path) && content.blogArticle) {
		const article = content.blogArticle;
		page = {
			title: article.title,
			description: excerpt(article.content) || `Read ${article.title} by Stan Runge.`
		};
		type = 'article';
		modifiedAt = date(article.updatedAt);
	} else if (/^\/blog\/[^/]+\/edit$/.test(path) && content.blogArticle) {
		page = { title: `Editing ${content.blogArticle.title}`, description: 'Edit a blog article.' };
	} else if (/^\/lists\/[^/]+$/.test(path) && content.list) {
		const list = content.list;
		const names = list.items.slice(0, 3).map((item) => item.name);
		page = {
			title: list.name,
			description: names.length
				? `${list.name}: ${names.join(', ')}${list.items.length > names.length ? ', and more' : ''}.`
				: `${list.name}, a ${list.isProgress ? 'progress ' : ''}list by Stan Runge.`
		};
	} else if (/^\/projects\/derby\/[^/]+$/.test(path) && content.race) {
		const race = content.race;
		page = {
			title: `${race.short} · Derby Lens`,
			description: `Estimate odds for the ${race.short}, a ${race.distance} m ${race.discipline} race.`
		};
	}

	return {
		title: page ? formatTitle(page.title, environment) : getTitle(path, environment),
		description: page?.description ?? 'Stan Runge’s personal website.',
		url,
		indexable: !!page && !environment && !/^\/blog\/[^/]+\/edit$/.test(path),
		type,
		image: `${SITE_ORIGIN}/moon.jpg`,
		imageAlt: 'Moon icon for Stan Runge’s website',
		modifiedAt
	};
}