CodeCoverageHelper.cls

public class CodeCoverageHelper {
    
    //This method will return a Map of Classes Names and the respective Code Coverage
    public static Map<String, Decimal> getCodeCoverage() {
        Map<String, Decimal> resultMap = new Map<String, Decimal>();

        string queryStr = 'SELECT+NumLinesCovered,ApexClassOrTriggerId,ApexClassOrTrigger.Name,NumLinesUncovered,Coverage+FROM+ApexCodeCoverageAggregate+ORDER+BY+ApexClassOrTrigger.Name';

        String ENDPOINT = 'https://' + System.URL.getSalesforceBaseUrl().getHost() + '/services/data/v40.0/tooling/';
        
        HttpRequest req = new HttpRequest();
        
        req.setEndpoint(ENDPOINT + 'query/?q=' + queryStr);
        req.setHeader('Authorization', 'Bearer ' + UserInfo.getSessionID());
        req.setHeader('Content-Type', 'application/json');
        req.setMethod('GET');
        req.setTimeout(80000);

        Http http = new Http();
        HTTPResponse res = http.send(req);

        if (res.getStatusCode() == 200) {
            CodeCoverageWrapper codeCoverageWrapper = CodeCoverageWrapper.parse(res.getBody());
            
            for(CodeCoverageWrapper.Records records : codeCoverageWrapper.records) {
                
                String classOrTriggerName  = records.ApexClassOrTrigger.Name;
                Decimal numLinesCovered    = records.NumLinesCovered;
                Decimal numLinesUncovered  = records.NumLinesUncovered;
                Decimal totalNumberOfLines = numLinesCovered + numLinesUncovered;

                if(totalNumberOfLines == 0) continue;

                Decimal coveragePercentage = (numLinesCovered / totalNumberOfLines) * 100;

                resultMap.put(classOrTriggerName, coveragePercentage);
            }
        }

        return resultMap;
    }

    // Method created to sort the Map of Coverage values in Descending Order
    public static Map<String, Decimal> sortCodeCoverageMapByCoverage(Map<String, Decimal> coverageMap) {
        CoverageWrapper[] coverageList = new CoverageWrapper[]{};

        for(String key : coverageMap.keySet()) {
            coverageList.add(new CoverageWrapper(key, coverageMap.get(key)));
        }
        
        coverageList.sort();

        CoverageWrapper[] finalList = new CoverageWrapper[]{};

        for(Integer i = coverageList.size() -1; i >= 0; i = i-1 ) {
            finalList.add(coverageList.get(i));
        }

        Map<String,Decimal> coverageToNameMap = new Map<String,Decimal>();

        for(CoverageWrapper coverage : finalList) {
            coverageToNameMap.put(coverage.getObjectName(), coverage.getValue());
        }

        return coverageToNameMap;
    }

    public static String buildCodeCoverageMessage(Decimal coverage, String objectName) {
        String coverageMessage = ''; 
        
        if(coverage < 10) {
            coverageMessage = coverageMessage + ICON_ERROR + ' ' + MESSAGE_UNDER_10 +  ' threshold';
        }
        
        if(coverage >= 10 && coverage < 75) {
            coverageMessage = coverageMessage + ICON_WARNING + ' ' + MESSAGE_UNDER_75 + ' threshold';
        }

        if(coverage >= 75) {
            coverageMessage = coverageMessage + ICON_OK + ' ' + MESSAGE_ABOVE_75 + ' threshold';
        }

        coverageMessage = coverageMessage + ' | Code Coverage for [ ' + objectName + ' ]: ' + coverage + '%'; 

        return coverageMessage;
    }

    public static final String ICON_ERROR   = '⛔';
    public static final String ICON_WARNING = '️⚠️';
    public static final String ICON_OK      = '✅';

    public static final String MESSAGE_UNDER_10 = 'Under the 10%';
    public static final String MESSAGE_UNDER_75 = 'Under the 75%';
    public static final String MESSAGE_ABOVE_75 = 'Above the 75%';

    public class CoverageWrapper implements Comparable {
        private Decimal coverageValue{get; set;}
        private String objectName    {get; set;}
        private Integer intValue     {get; set;}

        CoverageWrapper(String objectName, Decimal coverageValue) {
            this.objectName = objectName;
            this.coverageValue = coverageValue;
            this.intValue = coverageValue.intValue();
        }

        public Decimal getValue() {
            return this.coverageValue;
        }

        public String getObjectName() {
            return this.objectName;
        }

        public Integer compareTo(Object other) {
            return intValue-((CoverageWrapper)other).intValue;
        }
    }
}