bot: add birthday command

PluralKit.Core/Utils.cs

@@ -1,4 +1,11 @@
 using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text.RegularExpressions;
+using NodaTime;
+using NodaTime.Text;
 
 
 namespace PluralKit
@@ -27,6 +34,66 @@ namespace PluralKit
             if (str != null) return str.Length > length;
             return false;
         }
+
+        public static Duration? ParsePeriod(string str)
+        {
+            
+            Duration d = Duration.Zero;
+            
+            foreach (Match match in Regex.Matches(str, "(\\d{1,3})(\\w)"))
+            {
+                var amount = int.Parse(match.Groups[1].Value);
+                var type = match.Groups[2].Value;
+
+                if (type == "w") d += Duration.FromDays(7) * amount;
+                else if (type == "d") d += Duration.FromDays(1) * amount;
+                else if (type == "h") d += Duration.FromHours(1) * amount;
+                else if (type == "m") d += Duration.FromMinutes(1) * amount;
+                else if (type == "s") d += Duration.FromSeconds(1) * amount;
+                else return null;
+            }
+
+            if (d == Duration.Zero) return null;
+            return d;
+        }
+
+        public static LocalDate? ParseDate(string str, bool allowNullYear = false)
+        {
+            // NodaTime can't parse constructs like "1st" and "2nd" so we quietly replace those away
+            // Gotta make sure to do the regex otherwise we'll catch things like the "st" in "August" too
+            str = Regex.Replace(str, "(\\d+)(st|nd|rd|th)", "$1");
+            
+            var patterns = new[]
+            {
+                "MMM d yyyy",   // Jan 1 2019
+                "MMM d, yyyy",  // Jan 1, 2019
+                "MMMM d yyyy",  // January 1 2019
+                "MMMM d, yyyy", // January 1, 2019
+                "yyyy-MM-dd",   // 2019-01-01
+                "yyyy MM dd",   // 2019 01 01
+                "yyyy/MM/dd"   // 2019/01/01
+            }.ToList();
+
+            if (allowNullYear) patterns.AddRange(new[]
+            {
+                "MMM d",        // Jan 1
+                "MMMM d",       // January 1
+                "MM-dd",        // 01-01
+                "MM dd",        // 01 01
+                "MM/dd"         // 01-01
+            });
+
+            // Giving a template value so year will be parsed as 0001 if not present
+            // This means we can later disambiguate whether a null year was given
+            // TODO: should we be using invariant culture here?
+            foreach (var pattern in patterns.Select(p => LocalDatePattern.CreateWithInvariantCulture(p).WithTemplateValue(new LocalDate(0001, 1, 1))))
+            {
+                var result = pattern.Parse(str);
+                if (result.Success) return result.Value;
+            }
+
+            return null;
+        }
     }
 
     public static class Emojis {