refactor: IpLookup lazy load reader

app/controllers/click.cr

@@ -30,7 +30,7 @@ module App::Controllers
 
             click = App::Models::Click.new
             click.link_id = link_id
-            click.country = client_ip ? IpLookup.country(client_ip).try(&.code) : nil
+            click.country = client_ip ? IpLookup.country(client_ip) : nil
             click.user_agent = user_agent_str
             click.browser = ua_parser.try(&.family)
             click.os = ua_parser.try(&.os.try(&.family))

app/lib/ip_lookup.cr

@@ -1,48 +1,45 @@
 require "maxminddb"
 require "log"
 
-struct IpLookup
-  MMDB_PATH = "data/GeoLite2-Country.mmdb"
+module App::Lib
+  struct IpLookup
+    MMDB_PATH = "data/GeoLite2-Country.mmdb"
 
-  record Country, code : String? = nil, name : String? = nil
+    @@reader : MaxMindDB::Reader? = nil
+    @@reader_mutex = Mutex.new
 
-  def self.country(ip_address : String) : Country?
-    return nil if ip_address == "Unknown" || ip_address.empty?
+    private def self.get_reader : MaxMindDB::Reader
+      @@reader_mutex.synchronize do
+        @@reader ||= MaxMindDB.open(MMDB_PATH)
+      end
+    end
 
-    begin
-      reader = MaxMindDB.open(MMDB_PATH)
-      lookup = reader.get(ip_address)
+    def self.country(ip_address : String) : String?
+      return nil if ip_address == "Unknown" || ip_address.empty?
 
-      country_code = lookup["country"]?.try &.["iso_code"]?.try &.as_s
-      country_name = lookup["country"]?.try &.["names"]?.try &.["en"]?.try &.as_s
-
-      if country_code || country_name
-        Country.new(
-          code: country_code,
-          name: country_name
-        )
-      else
+      begin
+        lookup = get_reader.get(ip_address)
+        lookup["country"]?.try &.["iso_code"]?.try &.as_s
+      rescue ex
+        Log.error { "IP lookup failed: #{ex.message}" }
         nil
       end
-    rescue ex
-      Log.error { "IP lookup failed: #{ex.message}" }
-      nil
     end
-  end
 
-  def self.ip_from_address(address_string : String?) : String?
-    return nil if address_string.nil?
+    def self.ip_from_address(address_string : String?) : String?
+      return nil if address_string.nil?
 
-    if address_string.includes?('[') # IPv6 with port: [2001:db8::1]:8080
-      address_string.split(']').first.sub('[', '\'')
-    elsif address_string.includes?(':')
-      if address_string.count(':') > 1 # IPv6 without port
+      if address_string.includes?('[') # IPv6 with port: [2001:db8::1]:8080
+        address_string.split(']').first.sub('[', '\'')
+      elsif address_string.includes?(':')
+        if address_string.count(':') > 1 # IPv6 without port
+          address_string
+        else # IPv4 with port: 192.168.1.1:8080
+          address_string.split(':').first
+        end
+      else # Address without port
         address_string
-      else # IPv4 with port: 192.168.1.1:8080
-        address_string.split(':').first
       end
-    else # Address without port
-      address_string
     end
   end
 end