Add ability to pipe input from a file

I'm sure there's a better way to strip the UTF-8 BOM from the beginning of the file (and/or use that information to actually handle the string appropriately) but this works for my use case. At this point, we support ASCII and UTF-8 in LE order with or without the byte-order mark and, I think, either \n or \n\r line endings as input text file formats.

src/01.cs

@@ -4,7 +4,7 @@ internal class Day01 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/01.txt");
+        var lines = Util.ReadAllLines("inputs/01.txt");
         Part1(lines);
         Part2(lines);
     }

src/02.cs

@@ -4,7 +4,7 @@ internal class Day02 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/02.txt");
+        var lines = Util.ReadAllLines("inputs/02.txt");
         var instructions = new List<Instruction>();
         foreach (var instruction in lines)
         {

src/03.cs

@@ -4,7 +4,7 @@ internal class Day03 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/03.txt");
+        var lines = Util.ReadAllLines("inputs/03.txt");
         Part1(lines);
         Part2(lines);
     }

src/05.cs

@@ -43,7 +43,7 @@ internal class Day05 : Day
 
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/05.txt");
+        var lines = Util.ReadAllLines("inputs/05.txt");
         List<Line> segments = new();
         foreach (var line in lines)
         {

src/08.cs

@@ -4,7 +4,7 @@ internal class Day08 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/08.txt");
+        var lines = Util.ReadAllLines("inputs/08.txt");
         List<(List<string>, List<string>)> puzzle = new();
         foreach (var line in lines)
         {

src/09.cs

@@ -4,7 +4,7 @@ internal class Day09 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/09.txt");
+        var lines = Util.ReadAllLines("inputs/09.txt").ToArray();
         byte[,] grid = new byte[lines.Length, lines[0].Length];
         for (int i = 0; i < lines.Length; i++)
         {

src/10.cs

@@ -4,7 +4,7 @@ internal class Day10 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/10.txt");
+        var lines = Util.ReadAllLines("inputs/10.txt");
         Part1(lines);
         Part2(lines);
     }

src/11.cs

@@ -4,7 +4,7 @@ internal class Day11 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/11.txt");
+        var lines = Util.ReadAllLines("inputs/11.txt").ToArray();
         var grid = new byte[lines.Length, lines[0].Length];
         for (int i = 0; i < lines.Length; i++)
         {

src/12.cs

@@ -4,7 +4,7 @@ internal class Day12 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/12.txt");
+        var lines = Util.ReadAllLines("inputs/12.txt");
         var paths = new Dictionary<string, List<string>>();
         foreach (var line in lines)
         {

src/13.cs

@@ -4,7 +4,7 @@ internal class Day13 : Day
 {
     internal override void Go()
     {
-        var lines = File.ReadAllLines("inputs/13.txt");
+        var lines = Util.ReadAllLines("inputs/13.txt");
         int phase = 0;
         var points = new HashSet<(int, int)>();
         var folds = new List<(char, int)>();

src/Template.cs

@@ -6,7 +6,7 @@ internal class DayTemplate : Day
     {
         Logger.Log("Day #");
         Logger.Log("-----");
-        var lines = File.ReadAllLines("inputs/##.txt");
+        var lines = Util.ReadAllLines("inputs/##.txt");
         Part1(lines);
         Part2(lines);
         Logger.Log("");

src/Util.cs

@@ -0,0 +1,32 @@
+using System.Text;
+
+namespace aoc2021;
+
+internal static class Util
+{
+    internal static IEnumerable<string> ReadAllLines(string filename)
+    {
+        if (Console.IsInputRedirected)
+        {
+            string? line;
+            List<string> lines = new();
+            while ((line = Console.In.ReadLine()) != null)
+            {
+                if (!lines.Any())
+                {
+                    if (line.StartsWith(Encoding.UTF8.GetString(Encoding.UTF8.GetPreamble())))
+                    {
+                        line = line[Encoding.UTF8.GetPreamble().Length..];
+                    }
+                }
+                lines.Add(line);
+            }
+
+            return lines;
+        }
+        else
+        {
+            return File.ReadAllLines(filename);
+        }
+    }
+}