feat: mvp (#1)

MVP including features:
* Detect IP change
* Configurable/generic external IP provider
* Configurable/generic DNS provider
* Impl. of plain external IP provider
* Impl. of Ionos DNS provider

Reviewed-on: #1
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

pkg/changeDetector/changeDetector.go

@@ -0,0 +1,53 @@
+package changeDetector
+
+import (
+	"realdnydns/pkg/config"
+	"realdnydns/pkg/dnsProvider"
+	"realdnydns/pkg/externalIpProvider"
+)
+
+type ChangeDetector struct {
+	externalIpProvider externalIpProvider.ExternalIpProvider
+	dnsProvider        dnsProvider.DNSProvider
+	domains            []config.DomainConfig
+}
+
+func New(
+	externalIpProvider externalIpProvider.ExternalIpProvider,
+	dnsProvider dnsProvider.DNSProvider,
+	domains []config.DomainConfig,
+) ChangeDetector {
+	return ChangeDetector{
+		externalIpProvider: externalIpProvider,
+		dnsProvider:        dnsProvider,
+		domains:            domains,
+	}
+}
+
+func (c *ChangeDetector) DetectAndApplyChanges() (int, error) {
+	externalIp, err := c.externalIpProvider.GetExternalIp()
+	if err != nil {
+		return 0, err
+	}
+
+	var numberUpdated int
+
+	for _, domain := range c.domains {
+		for _, subdomain := range domain.Subdomains {
+			currentRecord, err := c.dnsProvider.GetRecord(domain.TLD, subdomain)
+			if err != nil {
+				return numberUpdated, err
+			}
+
+			if currentRecord.IP != externalIp.String() {
+				_, err = c.dnsProvider.UpdateRecord(domain.TLD, subdomain, externalIp, currentRecord.TTL, currentRecord.Prio, currentRecord.Disabled)
+				numberUpdated++
+				if err != nil {
+					return numberUpdated, err
+				}
+			}
+		}
+	}
+
+	return numberUpdated, nil
+}