feat: add mode selecting (#15)

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

pkg/config/config.go

@@ -1,17 +1,15 @@
 package config
 
 import (
+	"errors"
+	"fmt"
 	"os"
 
 	"gopkg.in/yaml.v3"
 )
 
-type DomainConfig struct {
-	TLD        string   `yaml:"tld"`
-	Subdomains []string `yaml:"subdomains"`
-}
-
 type Config struct {
+	Mode                 string                     `yaml:"mode"`
 	ExternalIPProvider   ExternalIpProviderConfig   `yaml:"ip_provider"`
 	DNSProvider          DNSProviderConfig          `yaml:"dns_provider"`
 	NotificationProvider NotificationProviderConfig `yaml:"notification_provider,omitempty"`
@@ -19,6 +17,16 @@ type Config struct {
 	CheckInterval        string                     `yaml:"check_interval"`
 }
 
+const (
+	RunOnceMode    = "RunOnce"
+	ScheduledMode  = "Scheduled"
+)
+
+type DomainConfig struct {
+	TLD        string   `yaml:"tld"`
+	Subdomains []string `yaml:"subdomains"`
+}
+
 type ExternalIpProviderConfig struct {
 	Type           string    `yaml:"type"`
 	ProviderConfig yaml.Node `yaml:"config"`
@@ -35,15 +43,30 @@ type NotificationProviderConfig struct {
 }
 
 func (c *Config) Load(filePath string) error {
-	err := yaml.Unmarshal([]byte(filePath), c)
+	inputConfig, err := os.ReadFile(filePath)
 	if err != nil {
-		inputConfig, err := os.ReadFile(filePath)
-		if err != nil {
-			return err
-		}
-
-		return yaml.Unmarshal(inputConfig, c)
+		return fmt.Errorf("failed to read config file: %w", err)
 	}
 
-	return err
+	if err := yaml.Unmarshal(inputConfig, c); err != nil {
+		return fmt.Errorf("failed to unmarshal config file: %w", err)
+	}
+
+	if err := c.validate(); err != nil {
+		return fmt.Errorf("failed to validate config: %w", err)
+	}
+
+	return nil;
 }
+
+func (c *Config) validate() error {
+	if c.Mode != RunOnceMode && c.Mode != ScheduledMode {
+		return errors.New("mode must be one of 'RunOnce' or 'Scheduled'")
+	}
+
+	if c.Mode == ScheduledMode && c.CheckInterval == "" {
+		return errors.New("check interval must be set when mode is 'Scheduled'")
+	}
+
+	return nil;
+}