Port of example from Re-Engineering Legacy Software book

BannerAdChooser.cs

public class BannerAdChooser
{
    private readonly BannerDao bannerDao = new BannerDao();
    private readonly BannerCache cache = new BannerCache();

    public Banner GetAd(Player player, Page page)
    {
        Banner banner;
        bool showBanner = true;

        // First try the cache
        banner = cache.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.Equals("profile"))
        {
            // Don't show ads on player profile page
            showBanner = false;
        }

        if (page.Id.Equals("top") && DateTime.Now.DayOfWeek == DayOfWeek.Wednesday)
        {
            // No ads on top page on Wednesdays
            showBanner = false;
        }

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

        if (showBanner && banner == null)
        {
            banner = 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
        cache.Put(player, page, banner, 30 * 60);

        // Dozens more checks and conditions ...

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

        return banner;
    }
}