using System;

using System.Linq;

using System.Collections.Generic;

using Newtonsoft.Json; //just for displaying output

​

public class Program 

{

    public static void Main()

    {

        var prp = new ProviderRequestParameters();

        var sps = new SearchParameterSet(prp);

​

        Console.WriteLine(JsonConvert.SerializeObject(sps, Formatting.Indented)); //convert to json for display purposes

    }

}   

​

public class SearchParameterSet

{

    //Assumption: based on your code I assume you have properties something like this

    public ProviderRequestParameters ProviderParameters {get;set;}

    private IList<string> patientIds = new List<string>();

    public IList<string> PatientIds {get{return patientIds;} set {patientIds = value;}} 

    private IList<string> caseIds = new List<string>();

    public IList<string> CaseIds {get{return caseIds;} set {caseIds = value;}} 

    public DateTime DateFrom {get;set;} 

    public DateTime DateTo {get;set;} 

    public string Profile {get;set;} 

    public string Format {get;set;} 

    public string ResourceType {get;set;} 

    public string User {get;set;} 

​

    //actual changes below based on the above assumptions

    public SearchParameterSet(ProviderRequestParameters requestParameters)

    {

        var rParams = requestParameters.RequestParameters;

​

        ProviderParameters = requestParameters;

        PatientIds.AddRange(RequestParameterHelper.GetValueOrDefault<IEnumerable<string>>(rParams, FhirRequestParameters.ByPatient, RequestParameterHelper.ReturnCsvStrings));

        CaseIds.AddRange(RequestParameterHelper.GetValueOrDefault<IEnumerable<string>>(rParams, FhirRequestParameters.ByCase, RequestParameterHelper.ReturnCsvStrings));

        DateFrom = RequestParameterHelper.GetValueOrDefault<DateTime>(rParams, FhirRequestParameters.ByDateFrom, RequestParameterHelper.ReturnDate);

        DateTo = RequestParameterHelper.GetValueOrDefault<DateTime>(rParams, FhirRequestParameters.ByDateTo, RequestParameterHelper.ReturnDate);

        Profile = RequestParameterHelper.GetValueOrDefault<string>(rParams, FhirRequestParameters.Profile, RequestParameterHelper.ReturnString);

        Format = RequestParameterHelper.GetValueOrDefault<string>(rParams, FhirRequestParameters.Format, RequestParameterHelper.ReturnString);

        ResourceType = RequestParameterHelper.GetValueOrDefault<string>(rParams, FhirRequestParameters.ResourceType, RequestParameterHelper.ReturnString);

        User = RequestParameterHelper.GetValueOrDefault<string>(rParams, FhirRequestParameters.ByUser, RequestParameterHelper.ReturnString);

    }

}

​

public static class RequestParameterHelper

{

    public static T GetValueOrDefault<T>(IDictionary<string, string> requestParameters, string key, Func<string, T> parseValue)

    {

        string value = null;

        var parameterName = FhirSearchExtensions.RequestParameterNames[key]; //Ideally we wouldn't need this, but I don't know your code well enough to say if we can remove it

        requestParameters.TryGetValue(parameterName, out value); //or use key if the above line can be removed

        return parseValue(value);   

    }

    public static string ReturnString(string value)

    {

        return value;

    }

    public static DateTime ReturnDate(string value)

    {

        DateTime result; //I had to split the declaration from the following line for this editor

        return DateTime.TryParse(value, out result) ? result : DateTime.MinValue;

    }

    public static IEnumerable<string> ReturnCsvStrings(string value)

    {

        if (value == null) return Enumerable.Empty<string>();

        return value.Split(new char[] { ',' }, StringSplitOptions.RemoveEmptyEntries);

    }

}

​

// stuff for testing / no idea what your real code looks like so just threw this sample data together

public static class FhirRequestParameters

{

    public static readonly string ByPatient = "patient";

    public static readonly string ByCase = "case";

    public static readonly string ByDateFrom = "datefrom";

    public static readonly string ByDateTo = "dateto";

    public static readonly string Profile = "profile";

    public static readonly string Format = "format";

    public static readonly string ResourceType = "resourceType";

    public static readonly string ByUser = "user";

}

​

public static class FhirSearchExtensions

{

    static FhirSearchExtensions()

    {

        RequestParameterNames = new Dictionary<string,string>()

        {

            {FhirRequestParameters.ByPatient, FhirRequestParameters.ByPatient}

            ,{FhirRequestParameters.ByCase, FhirRequestParameters.ByCase}

            ,{FhirRequestParameters.ByDateFrom, FhirRequestParameters.ByDateFrom}

            ,{FhirRequestParameters.ByDateTo, FhirRequestParameters.ByDateTo}

            ,{FhirRequestParameters.Profile, FhirRequestParameters.Profile}

            ,{FhirRequestParameters.Format, FhirRequestParameters.Format}

            ,{FhirRequestParameters.ResourceType, FhirRequestParameters.ResourceType}

            ,{FhirRequestParameters.ByUser, FhirRequestParameters.ByUser}

        };

    }

    public static IDictionary<string, string> RequestParameterNames {get;set;}

}

​

public class ProviderRequestParameters

{

    public IDictionary<string,string> RequestParameters{get {return DefaultValue();}}

    IDictionary<string,string> DefaultValue()

    {

        return new Dictionary<string,string>()

        {

            {FhirRequestParameters.ByPatient, "patient1,patient2"}

            //,{FhirRequestParameters.ByCase, "case1,case2,case3"} //what happens if we leave this array unassigned?  All works as expected :)

            ,{FhirRequestParameters.ByDateFrom, "2018-09-02"}

            ,{FhirRequestParameters.ByDateTo, null}

            //,{FhirRequestParameters.Profile, /*does not exist in dictionary*/}

            ,{FhirRequestParameters.Format, "Format 1"}

            ,{FhirRequestParameters.ResourceType, "RT1"}

            ,{FhirRequestParameters.ByUser, "The User"}

        };

    }

}

​

public static class IListExtension //thanks to https://stackoverflow.com/a/33104162/361842

{

    public static void AddRange<T>(this IList<T> list, IEnumerable<T> items)

    {

        if (list == null) throw new ArgumentNullException("list");

        if (items == null) throw new ArgumentNullException("items");

​

        if (list is List<T>)

        {

            ((List<T>)list).AddRange(items);

        }

        else

        {

            foreach (var item in items)

            {

                list.Add(item);

            }

        }

    }

}

​