Read the zone lists in the country file

The # blocks in wl_cty.dat list CQ and ITU zones by call area and the
first letter after the digit, written with the main prefix letters. A call
now takes them whatever its own prefix letters are, so RA9Y and RM9I get
what UA9Y gets, as in N1MM. A call whose own prefix rule gives a zone, and
a whole-call entry, are left as they are.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/Nonemm.Core/Country/CountryFile.cs

@@ -1,25 +1,29 @@
 using System.Globalization;
+using System.Text.RegularExpressions;
 
 namespace Nonemm.Core.Country;
 
 /// The country file (`cty.dat` or `wl_cty.dat`), which says which entity, zone
 /// and continent a callsign belongs to.
-public sealed class CountryFile
+public sealed partial class CountryFile
 {
     private readonly Dictionary<string, PrefixRule> exactCalls;
     private readonly Dictionary<string, PrefixRule> prefixes;
+    private readonly Dictionary<DxccEntity, List<PrefixRule>> zoneRules;
     private readonly int longestPrefix;
 
     private CountryFile(
         IReadOnlyList<DxccEntity> entities,
         Dictionary<string, PrefixRule> exactCalls,
         Dictionary<string, PrefixRule> prefixes,
+        Dictionary<DxccEntity, List<PrefixRule>> zoneRules,
         string version)
     {
         Entities = entities;
         Version = version;
         this.exactCalls = exactCalls;
         this.prefixes = prefixes;
+        this.zoneRules = zoneRules;
         longestPrefix = prefixes.Count == 0 ? 0 : prefixes.Keys.Max(k => k.Length);
     }
 
@@ -38,16 +42,37 @@ public sealed class CountryFile
         List<DxccEntity> entities = [];
         Dictionary<string, PrefixRule> exactCalls = new(StringComparer.Ordinal);
         Dictionary<string, PrefixRule> prefixes = new(StringComparer.Ordinal);
+        Dictionary<DxccEntity, List<PrefixRule>> zoneRules = [];
         DxccEntity? current = null;
         string version = "";
+        bool isInZoneBlock = false;
 
         foreach (string rawLine in text.Split('\n'))
         {
             string line = rawLine.TrimEnd('\r', ' ', '\t');
-            if (line.Length == 0 || line.StartsWith('#'))
+            if (line.Length == 0)
             {
                 continue;
             }
+            if (line.StartsWith('#'))
+            {
+                // `#   UA9: UA9H(18)[31],...;` is a comment to a program that
+                // ignores it and a list of zones by call area to one that
+                // reads it. It can run on over the lines that follow.
+                if (current is not null && ZoneBlockStart.Match(line) is { Success: true } start)
+                {
+                    AddZoneRules(zoneRules, current, start.Groups[1].Value);
+                    isInZoneBlock = !line.EndsWith(';');
+                }
+                continue;
+            }
+            if (isInZoneBlock && char.IsWhiteSpace(rawLine[0]) && current is not null)
+            {
+                // the lines the block runs over are also read as aliases below,
+                // which is what makes UA9X a European Russia prefix
+                AddZoneRules(zoneRules, current, line);
+                isInZoneBlock = !line.EndsWith(';');
+            }
             if (!char.IsWhiteSpace(rawLine[0]))
             {
                 current = ParseHeader(line);
@@ -75,7 +100,7 @@ public sealed class CountryFile
         {
             throw new FormatException("country file holds no entities");
         }
-        return new CountryFile(entities, exactCalls, prefixes, version);
+        return new CountryFile(entities, exactCalls, prefixes, zoneRules, version);
     }
 
     public CountryLookup? Find(Callsign call)
@@ -94,9 +119,73 @@ public sealed class CountryFile
         }
         return IsGuantanamoException(call)
             ? FindByPrefix("K")
-            : FindByPrefix(call.EntityLookupText());
+            : FindByPrefix(call.EntityLookupText()) is { } found
+                ? WithZoneByCallArea(found, call.EntityLookupText())
+                : null;
     }
 
+    /// The zone block of the file (`#   UA9: UA9H(18)[31],...`) lists zones by
+    /// call area and the first letter after the digit, written with the
+    /// prefix letters of the entity's main prefix. N1MM reads it for every
+    /// call of the entity, whatever its own prefix letters are, so RA9Y and
+    /// RM9I get what UA9Y gets. A call whose own prefix rule already gives a
+    /// zone, such as VO2, is left as it is.
+    private CountryLookup WithZoneByCallArea(CountryLookup found, string text)
+    {
+        if (!zoneRules.TryGetValue(found.Entity, out List<PrefixRule>? rules)
+            || found.CqZone != found.Entity.CqZone
+            || found.ItuZone != found.Entity.ItuZone)
+        {
+            return found;
+        }
+        int digit = text.IndexOfAny(['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']);
+        if (digit < 1)
+        {
+            return found;
+        }
+        string tail = text[digit..];
+        foreach (PrefixRule rule in rules)
+        {
+            int rulesDigit = rule.Key.IndexOfAny(['0', '1', '2', '3', '4', '5', '6', '7', '8', '9']);
+            if (rulesDigit >= 1 && (rule.Key[..rulesDigit] + tail).StartsWith(rule.Key, StringComparison.Ordinal))
+            {
+                return found with
+                {
+                    CqZone = rule.CqZoneOverride ?? found.CqZone,
+                    ItuZone = rule.ItuZoneOverride ?? found.ItuZone,
+                };
+            }
+        }
+        return found;
+    }
+
+    private static void AddZoneRules(
+        Dictionary<DxccEntity, List<PrefixRule>> zoneRules,
+        DxccEntity entity,
+        string list)
+    {
+        if (!zoneRules.TryGetValue(entity, out List<PrefixRule>? rules))
+        {
+            rules = [];
+            zoneRules[entity] = rules;
+        }
+        foreach (string item in list.TrimEnd(';').Split(',', StringSplitOptions.RemoveEmptyEntries))
+        {
+            PrefixRule rule = PrefixRule.Parse(entity, item.Trim());
+            if (rule.Key.Length > 0)
+            {
+                rules.Add(rule);
+            }
+        }
+        // the longest prefix first, so VE3 is read before a shorter VE
+        rules.Sort((a, b) => b.Key.Length.CompareTo(a.Key.Length));
+    }
+
+    [GeneratedRegex(@"^#\s+\w+:\s*(.*)$")]
+    private static partial Regex ZoneBlockStartPattern();
+
+    private static readonly Regex ZoneBlockStart = ZoneBlockStartPattern();
+
     /// The country file lists `KG4` as Guantanamo Bay, but only a three or five
     /// character call is Guantanamo: KG4NE is, KG4IGC is an ordinary US call.
     /// The file cannot say that, so every program that reads it carries the

src/Nonemm.Core/Country/PrefixRule.cs

@@ -33,6 +33,12 @@ public sealed class PrefixRule
 
     public string Key { get; }
 
+    /// The CQ zone the alias gives, or null when it leaves the entity's own.
+    public int? CqZoneOverride => cqZone;
+
+    /// The ITU zone the alias gives, or null when it leaves the entity's own.
+    public int? ItuZoneOverride => ituZone;
+
     public static PrefixRule Parse(DxccEntity entity, string alias)
     {
         string key = alias;