dnswatcher/internal/config/config.go

// 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
)

// ErrNoTargets is returned when no monitoring targets are configured.
var ErrNoTargets = errors.New(
	"no monitoring targets configured: set DNSWATCHER_TARGETS environment variable",
)

// ErrInvalidInterval is returned when DNSWATCHER_DNS_INTERVAL or
// DNSWATCHER_TLS_INTERVAL is set but is not a positive duration. An empty
// value counts as unset and means the default.
var ErrInvalidInterval = errors.New(
	"interval must be a positive duration such as 30m or 1h",
)

// 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
	SendTestNotification bool
	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", "/var/lib/"+name)
	viper.SetDefault("TARGETS", "")
	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", "")
	viper.SetDefault("SEND_TEST_NOTIFICATION", false)
}

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 := parseInterval("DNS_INTERVAL")
	if err != nil {
		return nil, err
	}

	tlsInterval, err := parseInterval("TLS_INTERVAL")
	if err != nil {
		return nil, err
	}

	domains, hostnames, err := parseAndValidateTargets()
	if err != nil {
		return nil, err
	}

	cfg := &Config{
		Port:                 viper.GetInt("PORT"),
		Debug:                viper.GetBool("DEBUG"),
		DataDir:              viper.GetString("DATA_DIR"),
		Domains:              domains,
		Hostnames:            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"),
		SendTestNotification: viper.GetBool("SEND_TEST_NOTIFICATION"),
		params:               params,
		log:                  log,
	}

	return cfg, nil
}

// parseInterval reads the DNSWATCHER_-prefixed setting key as a duration. A
// value that does not parse, or is zero or negative, is an error naming the
// variable and the value; an unset variable has its default from setupViper.
func parseInterval(key string) (time.Duration, error) {
	value := viper.GetString(key)

	interval, err := time.ParseDuration(value)
	if err != nil || interval <= 0 {
		return 0, fmt.Errorf(
			"invalid DNSWATCHER_%s %q: %w", key, value, ErrInvalidInterval,
		)
	}

	return interval, nil
}

func parseAndValidateTargets() ([]string, []string, error) {
	domains, hostnames, err := ClassifyTargets(
		parseCSV(viper.GetString("TARGETS")),
	)
	if err != nil {
		return nil, nil, fmt.Errorf(
			"invalid targets configuration: %w", err,
		)
	}

	if len(domains) == 0 && len(hostnames) == 0 {
		return nil, nil, ErrNoTargets
	}

	return domains, hostnames, 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"
}