add DayFactory and cli options for day

Day.cs

@@ -0,0 +1,13 @@
+namespace aoc2019
+{
+    public abstract class Day
+    {
+        public virtual void AllParts()
+        {
+            Part1();
+            Part2();
+        }
+        public abstract void Part1();
+        public abstract void Part2();
+    }
+}

Day1.cs

@@ -5,21 +5,21 @@ using System.Linq;
 
 namespace aoc2019
 {
-    public class Day1
+    public class Day1 : Day
     {
-        private static IEnumerable<int> lines = 
+        private static readonly IEnumerable<int> lines =
             File.ReadLines("input/day1.in").Select(line => int.Parse(line));
 
         private static int FuelCost(int weight) => weight / 3 - 2;
 
-        public static void Part1()
+        public override void Part1()
         {
             Console.WriteLine(lines.Select(num => FuelCost(num)).Sum());
         }
 
         private static int FullCost(int cost)
         {
-            int total = 0, newcost = 0, tmp = cost;
+            int total = 0, newcost, tmp = cost;
 
             while ((newcost = FuelCost(tmp)) >= 0)
             {
@@ -30,7 +30,7 @@ namespace aoc2019
             return total;
         }
 
-        public static void Part2()
+        public override void Part2()
         {
             Console.WriteLine(lines.Select(cost => FullCost(cost)).Sum());
         }

Day2.cs

@@ -5,9 +5,9 @@ using System.Linq;
 
 namespace aoc2019
 {
-    public class Day2
+    public class Day2 : Day
     {
-        private static IEnumerable<int> input = 
+        private static readonly IEnumerable<int> input =
             File.ReadLines("input/day2.in")
             .First()
             .Split(',')
@@ -23,7 +23,7 @@ namespace aoc2019
                 }
         }
 
-        public static void Part1()
+        public override void Part1()
         {
             var output = input.ToList();
             output[1] = 12;
@@ -34,7 +34,7 @@ namespace aoc2019
             Console.WriteLine($"{output[0]}");
         }
 
-        public static void Part2()
+        public override void Part2()
         {
             List<int> output;
 

DayFactory.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace aoc2019
+{
+    internal class DayFactory
+    {
+        internal static Day GetDay(int daynum)
+        {
+            switch (daynum)
+            {
+                case 1: return new Day1();
+                case 2: return new Day2();
+                default: return null;
+            }
+        }
+    }
+}

Program.cs

@@ -1,6 +1,4 @@
 using System;
-using System.IO;
-using System.Linq;
 
 namespace aoc2019
 {
@@ -8,11 +6,29 @@ namespace aoc2019
     {
         static void Main(string[] args)
         {
-            Day1.Part1();
-            Day1.Part2();
-
-            Day2.Part1();
-            Day2.Part2();
+            if (args.Length == 1 && int.TryParse(args[0], out int daynum))
+            {
+                if (daynum >= 0 && daynum <= 25)
+                {
+                    Day day = DayFactory.GetDay(daynum);
+                    day.AllParts();
+                }
+                else
+                {
+                    Console.WriteLine($"{daynum} is an invalid day");
+                    return;
+                }
+            }
+            else
+            {
+                for (var i = 1; i <= 25; ++i)
+                {
+                    var day = DayFactory.GetDay(i);
+                    if (day == null) continue;
+                    Console.WriteLine($"Day {i}:");
+                    day.AllParts();
+                }
+            }
         }
     }
 }

aoc2019.csproj

@@ -5,4 +5,13 @@
     <TargetFramework>netcoreapp3.0</TargetFramework>
   </PropertyGroup>
 
+  <ItemGroup>
+    <None Update="input\day1.in">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+    <None Update="input\day2.in">
+      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
+    </None>
+  </ItemGroup>
+
 </Project>