Library

class Library {
    libraryName;
    subscribers;
    subscriptionTypes = {
        'normal': x => x.length,
        'special': x => x.length * 2,
        'vip': () => Number.MAX_SAFE_INTEGER
    };

    constructor(libraryName) {
        this.libraryName = libraryName;
        this.subscribers = [];
    }

    subscribe(name, type) {
        if (this.subscriptionTypes[type] === undefined) {
            throw new Error(`The type ${type} is invalid`);
        }
        let sub = this.subscribers.find(s => s.name === name);
        if (sub === undefined) {
            this.subscribers.push({name, type, books: []});
        } else {
            sub.type = type;
        }
        return sub;
    }

    unsubscribe(name) {
        let sub = this.subscribers.find(s => s.name === name);
        if (sub === undefined) {
            throw new Error(`There is no such subscriber as ${name}`);
        } else {
            this.subscribers.splice(this.subscribers.indexOf(sub), 1);
        }
        return this.subscribers;
    }

    receiveBook(name, title, author) {
        let sub = this.subscribers.find(s => s.name === name);
        if (sub === undefined) {
            throw new Error(`There is no such subscriber as ${name}`);
        } else {
            let max = this.subscriptionTypes[sub.type](name);
            if (sub.books.length < max) {
                sub.books.push({title, author});
            } else {
                throw new Error(`You have reached your subscription limit ${max}!`);
            }
        }
        return sub;
    }

    showInfo() {
        if (this.subscribers.length > 0) {
            let str = '';
            this.subscribers.map(s => {
                let books = s.books.map(b => `${b.title} by ${b.author.trim()}`).join(', ');
                str += `Subscriber: ${s.name}, Type: ${s.type}\nReceived books: ${books.trim()}\n`;
            })
            return str;

        } else {
            throw new Error(`${this.libraryName} has no information about any subscribers`);
        }
    }
}