Port of example from Re-Engineering Legacy Software book

BannerAdChooser.ts

export class BannerAdChooser {
    private readonly bannerDao = new BannerDao();
    private readonly bannerCache = new BannerCache();

    public getAd(player: Player, page: Page): Banner {
        let banner: Banner;
        let showBanner = true;

        // First try the cache
        banner = this.bannerCache.get(player, page);

        if (player.id === 23759) {
            // This player demands not to be shown any ads.
            // See support ticket #4839
            showBanner = false;
        }

        if (page.id === "profile") {
            // Don't show ads on player profile page
            showBanner = false;
        }

        if (page.id === "top" && new Date().getDay() === 3) {
            // No ads on top page on Wednesdays
            showBanner = false;
        }

        if (player.id % 5 === 0) {
            // A/B test - show banner 123 to these players
            banner = this.bannerDao.findById(123);
        }

        if (showBanner && banner == null) {
            banner = this.bannerDao.chooseRandomBanner();
        }

        if (banner.clientId === 393) {
            if (player.id === 36645) {
                // Bad blood between this client and this player!
                // Don't show the ad.
                showBanner = false;
            }
        }

        // Cache our choice for 30 minutes
        this.bannerCache.put(player, page, banner, 30 * 60);

        // Dozens more checks and conditions ...

        if (showBanner) {
            // Make a record of what banner we chose
            this.logImpression(player, page, banner);
        }

        return banner;
    }

    private logImpression(player: Player, page: Page, banner: Banner): void {
        // Implementation for logging the impression
    }
}