breaking: move maxmind config to config.providers

- moved maxmind to separate module
- code refactored
- simplified test

internal/maxmind/instance.go

@@ -0,0 +1,31 @@
+package maxmind
+
+import (
+	"github.com/yusing/go-proxy/internal/gperr"
+	"github.com/yusing/go-proxy/internal/task"
+)
+
+var instance *MaxMind
+
+func SetInstance(parent task.Parent, cfg *Config) gperr.Error {
+	newInstance := &MaxMind{Config: cfg}
+	if err := newInstance.LoadMaxMindDB(parent); err != nil {
+		return err
+	}
+	if instance != nil {
+		instance.task.Finish("updated")
+	}
+	instance = newInstance
+	return nil
+}
+
+func HasInstance() bool {
+	return instance != nil
+}
+
+func LookupCity(ip *IPInfo) (*City, bool) {
+	if instance == nil {
+		return nil, false
+	}
+	return instance.lookupCity(ip)
+}