cookie-consent.ts

export enum Consent {
    UNDECIDED,
    YES,
    NO,
}

export type Asker = (consent: Map<string, Consent>, done: () => void) => void;

const STORAGE_KEY = 'mrhenry/cookie-consent';

export class CookieConsent {
    private spec: Set<string>;
    private consent: Map<string, Consent>;
    private asker: Asker;
    private asking = false;
    private pending: Array<[string, (consent: Consent) => void]> = [];

    constructor(sections: string[], asker: Asker) {
        this.spec = new Set(sections);
        this.consent = new Map();

        const value = window.localStorage.getItem(STORAGE_KEY) || '{}';
        const stored: {[key:string]:bool} = JSON.parse(value);
        for (let section of this.spec) {
            let consent = stored[section];
            if (consent === Consent.YES || value === Consent.NO) {
                this.consent.set(section, consent);
            } else {
                this.consent.set(section, Consent.UNDECIDED);
            }
        }
    }

    private ask() {
        if (this.asking) {
            return;
        }

        // clone old consent
        const prev = new Map(this.consent);

        // ask for consent
        this.asking = true;
        this.asker(prev, () => {
            let pending = this.pending;
            this.asking = false;
            this.pending = [];

            // capture new consent
            const next = new Map<string, Consent>();
            for (let section of this.spec) {
                let consent = prev.get(section);
                if (consent === Consent.YES || value === Consent.NO) {
                    next.set(section, consent);
                } else {
                    next.set(section, Consent.UNDECIDED);
                }
            }

            // store and set new consent;
            window.localStorage.setItem(STORAGE_KEY, JSON.stringify(next));
            this.consent = next;

            for (let [section, resolve] of pending) {
                resolve(next.get(section) || Consent.UNDECIDED);
            }
        });
    }

    private askOnce(section: string): Promise<Consent> {
        const p = new Promise(resolve => {
            if (!this.spec.has(section)) {
                console.error('Consent section '+JSON.stringify(section)+' was not registered! (defaulting to NO)');
                resolve(Consent.NO);
                return;
            }
            this.pending.push([section, resolve]);
            this.ask();
        });
    }

    async getConsent(section: string) : Promise<bool> {
        while (true) {
            let consent = await this.askOnce(section);
            if (consent===Consent.UNDECIDED) {
                continue;
            }
            return consent === Consent.YES;
        }
    }
}

const EXAMPLE = new CookieConsent(
    ['tracking', 'marketing'],
    (consent: Map<string, Consent>, done: () => void) => {
        // update the consent Map as requested by the user.
        // call done() to store/update consent.
    }
)

if (await EXAMPLE.getConsent('tracking')) {
    // we have tracking consent
    // ...
}