feat: logging (#20)

Reviewed-on: #20
Co-authored-by: Timo Behrendt <t.behrendt@t00n.de>
Co-committed-by: Timo Behrendt <t.behrendt@t00n.de>

pkg/config/config.go

@@ -3,7 +3,9 @@ package config
 import (
 	"errors"
 	"fmt"
+	"log/slog"
 	"os"
+	"strings"
 
 	"gopkg.in/yaml.v3"
 )
@@ -15,6 +17,7 @@ type Config struct {
 	NotificationProvider NotificationProviderConfig `yaml:"notification_provider,omitempty"`
 	Domains              []DomainConfig             `yaml:"domains"`
 	CheckInterval        string                     `yaml:"check_interval"`
+	LogLevel             string                     `yaml:"log_level"`
 }
 
 const (
@@ -22,6 +25,18 @@ const (
 	ScheduledMode = "Scheduled"
 )
 
+var LogLevelMap = map[string]slog.Level{
+	"debug": slog.LevelDebug,
+	"info":  slog.LevelInfo,
+	"warn":  slog.LevelWarn,
+	"error": slog.LevelError,
+}
+
+func isValidLogLevel(level string) bool {
+	_, ok := LogLevelMap[strings.ToLower(level)]
+	return ok
+}
+
 type DomainConfig struct {
 	TLD        string   `yaml:"tld"`
 	Subdomains []string `yaml:"subdomains"`
@@ -68,5 +83,9 @@ func (c *Config) validate() error {
 		return errors.New("check interval must be set when mode is 'Scheduled'")
 	}
 
+	if c.LogLevel != "" && !isValidLogLevel(c.LogLevel) {
+		return fmt.Errorf("log level must be one of 'debug', 'info', 'warn', 'error', but got %s", c.LogLevel)
+	}
+
 	return nil
 }