Initial scaffold with per-nameserver DNS monitoring model

Full project structure following upaas conventions: uber/fx DI, go-chi
routing, slog logging, Viper config. State persisted as JSON file with
per-nameserver record tracking for inconsistency detection. Stub
implementations for resolver, portcheck, tlscheck, and watcher.

internal/config/config.go

@@ -0,0 +1,187 @@
+// Package config provides application configuration via Viper.
+package config
+
+import (
+	"errors"
+	"fmt"
+	"log/slog"
+	"strings"
+	"time"
+
+	"github.com/spf13/viper"
+	"go.uber.org/fx"
+
+	"sneak.berlin/go/dnswatcher/internal/globals"
+	"sneak.berlin/go/dnswatcher/internal/logger"
+)
+
+// Default configuration values.
+const (
+	defaultPort             = 8080
+	defaultDNSInterval      = 1 * time.Hour
+	defaultTLSInterval      = 12 * time.Hour
+	defaultTLSExpiryWarning = 7
+)
+
+// Params contains dependencies for Config.
+type Params struct {
+	fx.In
+
+	Globals *globals.Globals
+	Logger  *logger.Logger
+}
+
+// Config holds application configuration.
+type Config struct {
+	Port              int
+	Debug             bool
+	DataDir           string
+	Domains           []string
+	Hostnames         []string
+	SlackWebhook      string
+	MattermostWebhook string
+	NtfyTopic         string
+	DNSInterval       time.Duration
+	TLSInterval       time.Duration
+	TLSExpiryWarning  int
+	SentryDSN         string
+	MaintenanceMode   bool
+	MetricsUsername   string
+	MetricsPassword   string
+	params            *Params
+	log               *slog.Logger
+}
+
+// New creates a new Config instance from environment and config files.
+func New(_ fx.Lifecycle, params Params) (*Config, error) {
+	log := params.Logger.Get()
+
+	name := params.Globals.Appname
+	if name == "" {
+		name = "dnswatcher"
+	}
+
+	setupViper(name)
+
+	cfg, err := buildConfig(log, &params)
+	if err != nil {
+		return nil, err
+	}
+
+	configureDebugLogging(cfg, params)
+
+	return cfg, nil
+}
+
+func setupViper(name string) {
+	viper.SetConfigName(name)
+	viper.SetConfigType("yaml")
+	viper.AddConfigPath("/etc/" + name)
+	viper.AddConfigPath("$HOME/.config/" + name)
+	viper.AddConfigPath(".")
+
+	viper.SetEnvPrefix("DNSWATCHER")
+	viper.AutomaticEnv()
+
+	// PORT is not prefixed for compatibility
+	_ = viper.BindEnv("PORT", "PORT")
+
+	viper.SetDefault("PORT", defaultPort)
+	viper.SetDefault("DEBUG", false)
+	viper.SetDefault("DATA_DIR", "./data")
+	viper.SetDefault("DOMAINS", "")
+	viper.SetDefault("HOSTNAMES", "")
+	viper.SetDefault("SLACK_WEBHOOK", "")
+	viper.SetDefault("MATTERMOST_WEBHOOK", "")
+	viper.SetDefault("NTFY_TOPIC", "")
+	viper.SetDefault("DNS_INTERVAL", defaultDNSInterval.String())
+	viper.SetDefault("TLS_INTERVAL", defaultTLSInterval.String())
+	viper.SetDefault("TLS_EXPIRY_WARNING", defaultTLSExpiryWarning)
+	viper.SetDefault("SENTRY_DSN", "")
+	viper.SetDefault("MAINTENANCE_MODE", false)
+	viper.SetDefault("METRICS_USERNAME", "")
+	viper.SetDefault("METRICS_PASSWORD", "")
+}
+
+func buildConfig(
+	log *slog.Logger,
+	params *Params,
+) (*Config, error) {
+	err := viper.ReadInConfig()
+	if err != nil {
+		var notFound viper.ConfigFileNotFoundError
+		if !errors.As(err, &notFound) {
+			log.Error("config file malformed", "error", err)
+
+			return nil, fmt.Errorf(
+				"config file malformed: %w", err,
+			)
+		}
+	}
+
+	dnsInterval, err := time.ParseDuration(
+		viper.GetString("DNS_INTERVAL"),
+	)
+	if err != nil {
+		dnsInterval = defaultDNSInterval
+	}
+
+	tlsInterval, err := time.ParseDuration(
+		viper.GetString("TLS_INTERVAL"),
+	)
+	if err != nil {
+		tlsInterval = defaultTLSInterval
+	}
+
+	cfg := &Config{
+		Port:              viper.GetInt("PORT"),
+		Debug:             viper.GetBool("DEBUG"),
+		DataDir:           viper.GetString("DATA_DIR"),
+		Domains:           parseCSV(viper.GetString("DOMAINS")),
+		Hostnames:         parseCSV(viper.GetString("HOSTNAMES")),
+		SlackWebhook:      viper.GetString("SLACK_WEBHOOK"),
+		MattermostWebhook: viper.GetString("MATTERMOST_WEBHOOK"),
+		NtfyTopic:         viper.GetString("NTFY_TOPIC"),
+		DNSInterval:       dnsInterval,
+		TLSInterval:       tlsInterval,
+		TLSExpiryWarning:  viper.GetInt("TLS_EXPIRY_WARNING"),
+		SentryDSN:         viper.GetString("SENTRY_DSN"),
+		MaintenanceMode:   viper.GetBool("MAINTENANCE_MODE"),
+		MetricsUsername:   viper.GetString("METRICS_USERNAME"),
+		MetricsPassword:   viper.GetString("METRICS_PASSWORD"),
+		params:            params,
+		log:               log,
+	}
+
+	return cfg, nil
+}
+
+func parseCSV(input string) []string {
+	if input == "" {
+		return nil
+	}
+
+	parts := strings.Split(input, ",")
+	result := make([]string, 0, len(parts))
+
+	for _, part := range parts {
+		trimmed := strings.TrimSpace(part)
+		if trimmed != "" {
+			result = append(result, trimmed)
+		}
+	}
+
+	return result
+}
+
+func configureDebugLogging(cfg *Config, params Params) {
+	if cfg.Debug {
+		params.Logger.EnableDebugLogging()
+		cfg.log = params.Logger.Get()
+	}
+}
+
+// StatePath returns the full path to the state JSON file.
+func (c *Config) StatePath() string {
+	return c.DataDir + "/state.json"
+}