Add automatic input downloading

Since we no longer include input files with the solution, per AoC guidelines, this will enable other users to use this application (after specifying their session token) without manually grabbing all the appropriate download files.

src/main.cs

@@ -39,40 +39,88 @@ if (runPart1 != null || runPart2 != null)
 
 if (runAll)
 {
+    desiredDays.Clear();
     foreach (var type in types)
     {
-        using var day = (Day)Activator.CreateInstance(type)!;
-        day.Go(runPart1 ?? true, runPart2 ?? true);
+        desiredDays.Add(type.Name[^2..]);
+    }
+}
+
+if (desiredDays.Count == 0)
+{
+    desiredDays.Add("");
+}
+
+var getDayNumFromArg = (string arg) =>
+{
+    if (string.IsNullOrEmpty(arg))
+    {
+        arg = types.Last().ToString()[^2..];
+    }
+
+    return int.Parse(arg);
+};
+
+var getDayInstanceFromArg = (string arg) =>
+{
+    var num = getDayNumFromArg(arg);
+    var typ = types.FirstOrDefault(x => x.Name == $"Day{num.ToString().PadLeft(2, '0')}");
+    if (typ == null)
+    {
+        return null;
+    }
+
+    var day = (Day?) Activator.CreateInstance(typ);
+    return day;
+};
+
+aoc2024.Util.DotEnv.SetEnvironment();
+var sessionVal = Environment.GetEnvironmentVariable("AOC_SESSION");
+if (!string.IsNullOrEmpty(sessionVal))
+{
+    var year = Environment.GetEnvironmentVariable("AOC_YEAR");
+    if (string.IsNullOrEmpty(year))
+    {
+        // was going to use the current year, but this solution is specifically designed for a certain year, so using that makes more sense.
+        // don't forget your find/replace when copying this code for a new aoc year!
+        //year = DateTime.Now.Year.ToString();
+        year = "2024";
+        System.Diagnostics.Debug.WriteLine($"No AOC_YEAR env var defined or set in .env file, so assuming year {year}");
+    }
+
+    foreach (var day in desiredDays)
+    {
+        var dayNum = getDayNumFromArg(day);
+        if (!File.Exists(Path.Combine("inputs", $"{dayNum.ToString().PadLeft(2, '0')}.txt")))
+        {
+            Logger.Log($"Downloading input for day {dayNum}...");
+            try
+            {
+                await aoc2024.Util.RetrieveInput.Get(sessionVal, year, dayNum);
+                Logger.LogLine("<green>done!<r>");
+            }
+            catch (Exception ex)
+            {
+                Logger.LogLine($"<red>failed!<r> {ex}");
+            }
+
+            Logger.LogLine("");
+        }
     }
 }
 else
 {
-    if (desiredDays.Count == 0)
-    {
-        desiredDays.Add("");
-    }
-
-    foreach (var desiredDay in desiredDays)
-    {
-        Day? day = null;
-        if (string.IsNullOrEmpty(desiredDay))
-        {
-            day = (Day) Activator.CreateInstance(types.Last())!;
-        }
-        else
-        {
-            var type = types.FirstOrDefault(x => x.Name == $"Day{desiredDay.PadLeft(2, '0')}");
-            if (type == null)
-            {
-                Logger.LogLine($"Unknown day <cyan>{desiredDay}<r>");
-            }
-            else
-            {
-                day = (Day?) Activator.CreateInstance(type);
-            }
-        }
-
-        day?.Go(runPart1 ?? true, runPart2 ?? true);
-        day?.Dispose();
-    }
+    System.Diagnostics.Debug.WriteLine("No AOC_SESSION env var defined or set in .env file, so automatic input downloading not available.");
+}
+
+foreach (var desiredDay in desiredDays)
+{
+    Day? day = getDayInstanceFromArg(desiredDay);
+    if (day == null)
+    {
+        Logger.LogLine($"Unknown day <cyan>{desiredDay}<r>");
+    }
+
+    day?.Go(runPart1 ?? true, runPart2 ?? true);
+    day?.Dispose();
 }