Add Sprache package and enhance event occurrence parsing with new grammar rules

Core/Parsers/EventOccurrenceGrammar.cs

@@ -0,0 +1,153 @@
+using Sprache;
+using Core.Entities;
+using Core.Models;
+
+namespace Core.Parsers;
+
+/// <summary>
+/// Grammar definitions for parsing event occurrence DSL using parser combinators.
+/// Provides composable parsers for each grammar rule.
+/// </summary>
+public static class EventOccurrenceGrammar
+{
+    // Months - all 12 months supported
+    private static readonly Parser<string> January = Parse.String("January").Text().Token();
+    private static readonly Parser<string> February = Parse.String("February").Text().Token();
+    private static readonly Parser<string> March = Parse.String("March").Text().Token();
+    private static readonly Parser<string> April = Parse.String("April").Text().Token();
+    private static readonly Parser<string> May = Parse.String("May").Text().Token();
+    private static readonly Parser<string> June = Parse.String("June").Text().Token();
+    private static readonly Parser<string> July = Parse.String("July").Text().Token();
+    private static readonly Parser<string> August = Parse.String("August").Text().Token();
+    private static readonly Parser<string> September = Parse.String("September").Text().Token();
+    private static readonly Parser<string> October = Parse.String("October").Text().Token();
+    private static readonly Parser<string> November = Parse.String("November").Text().Token();
+    private static readonly Parser<string> December = Parse.String("December").Text().Token();
+
+    /// <summary>
+    /// Parser for month names (January through December).
+    /// </summary>
+    public static readonly Parser<string> Month = January
+        .Or(February)
+        .Or(March)
+        .Or(April)
+        .Or(May)
+        .Or(June)
+        .Or(July)
+        .Or(August)
+        .Or(September)
+        .Or(October)
+        .Or(November)
+        .Or(December);
+
+    /// <summary>
+    /// Parser for day of month (1-31, optional semicolon).
+    /// </summary>
+    public static readonly Parser<int> DayOfMonth = 
+        from day in Parse.Number
+        from semicolon in Parse.Char(';').Optional()
+        select int.Parse(day);
+
+    // Time parsing components
+    private static readonly Parser<string> Noon = Parse.String("NOON").Text().Token();
+    private static readonly Parser<string> Tbd = Parse.String("TBD").Text().Token();
+    
+    private static readonly Parser<string> AmPm = 
+        Parse.String("a.m.").Or(Parse.String("am")).Or(Parse.String("A.M.")).Or(Parse.String("AM"))
+        .Or(Parse.String("p.m.")).Or(Parse.String("pm")).Or(Parse.String("P.M.")).Or(Parse.String("PM"))
+        .Text().Token();
+
+    private static readonly Parser<string> TimeValue = 
+        from hour in Parse.Number
+        from colon in Parse.Char(':').Optional()
+        from minute in Parse.Number.Optional()
+        from ws in Parse.WhiteSpace.Many()
+        from ampm in AmPm
+        select $"{hour}:{(minute.IsDefined ? minute.Get() : "00")} {ampm}";
+
+    /// <summary>
+    /// Parser for hyphen characters (en-dash, hyphen, em-dash).
+    /// </summary>
+    public static readonly Parser<char> Hyphen = Parse.Char('–').Or(Parse.Char('-')).Or(Parse.Char('—'));
+
+    /// <summary>
+    /// Parser for time values, including ranges and special values (NOON, TBD).
+    /// </summary>
+    public static readonly Parser<string> Time = 
+        Noon.Or(Tbd)
+        .Or(
+            from start in TimeValue.Or(Noon)
+            from dash in Hyphen.Then(_ => Parse.WhiteSpace.Many()).Optional()
+            from end in TimeValue.Or(Noon).Optional()
+            select end.IsDefined 
+                ? $"{start} – {end.Get()}" 
+                : start
+        );
+
+    /// <summary>
+    /// Parser for section headers: EventName [–-—] (MS|HS).
+    /// </summary>
+    public static readonly Parser<(string EventName, string SchoolLevel)> SectionHeader =
+        from eventName in Parse.AnyChar.Except(Hyphen).Many().Text().Token()
+        from hyphen in Hyphen.Token()
+        from schoolLevel in Parse.String("MS").Or(Parse.String("HS")).Text().Token()
+        select (eventName.Trim(), schoolLevel);
+
+    /// <summary>
+    /// Parser for General Schedule/Session headers.
+    /// </summary>
+    public static readonly Parser<string> GeneralSchedule = 
+        Parse.String("General Schedule").Or(Parse.String("General Session")).Text().Token();
+
+    /// <summary>
+    /// Parser for comment lines (starting with #).
+    /// </summary>
+    public static readonly Parser<string> CommentLine = 
+        from hash in Parse.Char('#')
+        from rest in Parse.AnyChar.Many().Text()
+        select rest;
+
+    /// <summary>
+    /// Attempts to parse a section header from the given line.
+    /// Returns null if not a section header.
+    /// </summary>
+    public static (string EventName, string SchoolLevel)? TryParseSectionHeader(string line)
+    {
+        try
+        {
+            var result = SectionHeader.Parse(line);
+            return result;
+        }
+        catch
+        {
+            return null;
+        }
+    }
+
+    /// <summary>
+    /// Attempts to parse a General Schedule/Session header from the given line.
+    /// Returns null if not a General Schedule header.
+    /// </summary>
+    public static bool IsGeneralSchedule(string line)
+    {
+        try
+        {
+            GeneralSchedule.Parse(line);
+            return true;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
+    /// <summary>
+    /// Attempts to parse a comment line from the given line.
+    /// Returns true if the line is a comment.
+    /// </summary>
+    public static bool IsCommentLine(string line)
+    {
+        return line.TrimStart().StartsWith("#", StringComparison.Ordinal);
+    }
+}
+