refactor: simplify IsValidTimeZone to delegate to GetTimeZone (#54)

* feat: add class function TBundledTimeZone.IsValidTimeZone

* refactor: simplify IsValidTimeZone to delegate to GetTimeZone

Removes duplicated lock acquisition, zone scanning, and alias scanning
logic. GetTimeZone already handles all of this (including alias resolution),
so the implementation reduces to a simple try/except.

AIncludeAliases parameter is retained for API compatibility.

Also adds IsValidTimeZone declaration and implementation to src/TZDBPK/TZDB.pas
which was missing from the original PR.

---------

Co-authored-by: Havrlišan <20707187+havrlisan@users.noreply.github.com>
Co-authored-by: Alex Ciobanu <alex@ciobanu.org>

Author: 3 people

dist/TZDB.pas

@@ -208,6 +208,11 @@   TBundledTimeZone = class
     ///  <exception cref="TZDB|ETimeZoneInvalid">The specified ID cannot be found in the bundled database.</exception>
     class function GetTimeZone(const ATimeZoneID: string): TBundledTimeZone;
 
+    ///  <summary>Returns <c>True</c> if time zone exists.</summary>
+    ///  <param name="ATimeZoneID">The ID of the timezone to validate (ex. "Europe/Zagreb").</param>
+    ///  <param name="AIncludeAliases">Pass <c>True</c> to include time zone aliases into the validation.</param>
+    class function IsValidTimeZone(const ATimeZoneID: string; const AIncludeAliases: Boolean = False): Boolean;
+
     ///  <summary>Returns the version of the TZDB component.</summary>
     ///  <returns>A string representing the version of the source.</returns>
     class function Version: string;
@@ -12768,6 +12773,17 @@ class function TBundledTimeZone.GetTimezoneFromAlias(const AAliasID: string): st
   Result := GetTimeZone(AAliasID).ID;
 end;
 
+class function TBundledTimeZone.IsValidTimeZone(const ATimeZoneID: string; const AIncludeAliases: Boolean = False): Boolean;
+begin
+  try
+    GetTimeZone(ATimeZoneID);
+    Result := True;
+  except
+    on E: ETimeZoneInvalid do
+      Result := False;
+  end;
+end;
+
 function TBundledTimeZone.GetYearBreakdown(const AYear: Word): TYearSegmentArray;
 begin
   { Guard for upper and lower date/time limits }

src/TZDBPK/TZDB.pas

@@ -183,6 +183,12 @@   TBundledTimeZone = class
     ///  <exception cref="TZDB|ETimeZoneInvalid">The specified ID cannot be found in the bundled database.</exception>
     class function GetTimeZone(const ATimeZoneID: string): TBundledTimeZone;
 
+    ///  <summary>Checks if a given time zone ID is valid.</summary>
+    ///  <param name="ATimeZoneID">The ID of the timezone to validate (ex. "Europe/Zagreb").</param>
+    ///  <param name="AIncludeAliases">Pass <c>True</c> to include time zone aliases into the validation.</param>
+    ///  <returns><c>True</c> if the time zone ID is valid; <c>False</c> otherwise.</returns>
+    class function IsValidTimeZone(const ATimeZoneID: string; const AIncludeAliases: Boolean = False): Boolean;
+
     ///  <summary>Returns the version of the TZDB component.</summary>
     ///  <returns>A string representing the version of the source.</returns>
     class function Version: string;
@@ -1767,6 +1773,17 @@ class function TBundledTimeZone.GetTimeZone(const ATimeZoneID: string): TBundled
   end;
 end;
 
+class function TBundledTimeZone.IsValidTimeZone(const ATimeZoneID: string; const AIncludeAliases: Boolean = False): Boolean;
+begin
+  try
+    GetTimeZone(ATimeZoneID);
+    Result := True;
+  except
+    on E: ETimeZoneInvalid do
+      Result := False;
+  end;
+end;
+
 class function TBundledTimeZone.GetTimezoneFromAlias(const AAliasID: string): string;
 begin
   Result := GetTimeZone(AAliasID).ID;