OneLevelOfAbstractionPerFunction

CampaignServiceImplBad.java

public class CampaignServiceImpl {

    private static final double budgetMarginPercent = 0.03;
    private final CampaignCostService campaignCostService;

    /**** 
     * Read this and try to answer: when does a campaign have available funds? 
     *
     * Hard to answer because method deals with different abstraction levels - 
     * mixing the important business logic with the insignificant low-level details
     */ 
    public boolean hasAvailableFunds(Campaign campaign) {
        double margin = campaign.getBudget().getValue() * budgetMarginPercent;
        double dailyAvailableFunds = campaign.getBudget().getValue() - campaignCostService.getCampaignDailyCost(campaign.getChannelId(), campaign.getTimeZoneId());
        double actualAvailableFunds = dailyAvailableFunds - margin - campaign.getMaxCpm();
        return actualAvailableFunds > 0;
    }
}

CampaignServiceImplGood.java

public class CampaignServiceImpl {

    private static final double budgetMarginPercent = 0.03;
    private final CampaignCostService campaignCostService;

    /**** 
     * Read this and try to answer: when does a campaign have available funds? 
     * When (budget - spend - margin) is positive!
     *
     * Method deals with one "level": concepts like Budget, Spend and Margin; 
     * Does not deal with how each of these is computed (lower level of abstraction, e.g. applying percentage)
     */ 
    public boolean hasAvailableFunds(Campaign campaign) {
        final double remainingFunds = getBudget(campaign) - getTodaySpend(campaign) - safetyMargin(campaign); 
        return remainingFunds > 0;
    }
  
    private double getBudget(Campaign campaign) {
        return campaign.getBudget().getValue();
    }
  
    private double getTodaySpend(Campaign campaign) {
        return campaignCostService.getCampaignDailyCost(campaign.getChannelId(), campaign.getTimeZoneId());
    }
  
    private double safetyMargin(Campaign campaign) {
      return (getBudget(campaign) * budgetMarginPercent) + campaign.getMaxCpm();
    }
  
}