import { Link } from '../entities/Link';
import { User } from '../entities/User';
import { AppDataSource } from '../data-source';
import { getEnvString } from '../tools/jwt';

export type IdResponse = {
	id: number;
	exists: boolean;
};

export class LinkService {
	dataSource = AppDataSource;
	linkRepo = this.dataSource.getRepository(Link);

	// Retrieve config to check whether subdomains are allowed
	useSubdomains: boolean = getEnvString('useSubdomains', true) === 'true';

	/**
	 * Simply insert a new link entity anonymously.
	 *
	 * @param      {Link}     link    The link to insert
	 */
	async addAnonymous(link: Link): Promise<IdResponse> {
		let result: IdResponse = { id: -1, exists: false };

		// Sanity check: don't allow for adding links
		// with subdomains if server has it disabled.
		if (link.subdomain && !this.useSubdomains) link.subdomain = null;

		// Check if entry can be inserted.
		if (await this.canInsert(link)) {
			await this.linkRepo.insert(link);

			// Then get new link's ID
			const insertedLink: Link[] = await this.linkRepo.findBy({
				shortUri: link.shortUri,
				 fullUrl: link.fullUrl
			});

			// Return appropriate id (or error)
			if (insertedLink.length !== 1) {
				result.id = -2;
				result.exists = false;				
			} else {
				result.id = insertedLink[0].id;
				result.exists = true;
			}
		}

		return result;
	}

	/**
	 * Adds a new link entity, and links it with passed user.
	 * 
	 * USE ONLY FOR AUTHENTICATED USERS. For unauthenticated users
	 * use addAnonymous() instead. Returns IdResponse, containing
	 * exists field indicating if an existing field has been found,
	 * and if so, what is it's id. If exists is false, ID of the
	 * newly created entity gets returned.
	 * 
	 * Errors: an error ocurred if ID is negative.
	 * 
	 * This can be:
	 * 
	 * - -1 - link can't be inserted (because an entry with shortUri or shortUri+subdomain combo exist),
	 * 
	 * - -2 - no conflicting entry exists but transaction failed anyway.
	 * 
	 * @param      {Link}                 link    The link
	 * @param      {User}                 user    The user
	 * @return     {Promise<IdResponse>}  Dictionary containing link ID and whether it already existed, or was just inserted
	 */
	async addIfNew(link: Link, user: User): Promise<IdResponse> {

		let result: IdResponse = { id: -1, exists: false };

		// If no conflicts are found,
		// proceed with creating a new link entry.
		if (await this.canInsert(link)) {
			// Commit a transaction
			this.dataSource.transaction(async (t) => {
				link.author = user;
				user.links.push(link);
				t.insert(Link, link);
				t.save(user);
			});

			// Then get new link's ID
			const insertedLink: Link[] = await this.linkRepo.findBy({
				shortUri: link.shortUri,
				 fullUrl: link.fullUrl
			});

			// Return appropriate id (or error)
			if (insertedLink.length !== 1) {
				result.id = -2;
				result.exists = false;				
			} else {
				result.id = insertedLink[0].id;
				result.exists = true;
			}

		}

		return result;
	}

	async canInsert(link: Link): Promise<boolean> {
		let shortUriExists: boolean = true

		// If both subdomains are enabled, and user 
		// provided a subdomain, find if a record exists 
		// that either has the exact shortUri 
		// or shortUri and subdomain combo.
		// If any of these turns out to be true, the request 
		// must be invalidated and we can't proceed 
		// with creation of a new link.
		if (this.useSubdomains && link.subdomain)
		{
			shortUriExists = await this.linkRepo.existsBy({
				shortUri: link.shortUri,
				subdomain: link.subdomain
			});
		}
		// If custom subdomains are disabled, fallback to
		// checking only by the URIs - thus discarding
		// any possible subdomains.
		else
		{
			shortUriExists = await this.linkRepo.existsBy({ shortUri: link.shortUri });
		}

		return !shortUriExists;
	}

}