// 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("TARGETS", "")
	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
	}

	domains, hostnames, err := resolveTargets(log)
	if err != nil {
		return nil, fmt.Errorf("invalid targets configuration: %w", 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"),
		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()
	}
}

// resolveTargets merges DNSWATCHER_TARGETS with the deprecated
// DNSWATCHER_DOMAINS and DNSWATCHER_HOSTNAMES variables. When TARGETS
// is set, names are automatically classified using the Public Suffix
// List. Legacy variables are merged in and a deprecation warning is
// logged when they are used.
func resolveTargets(log *slog.Logger) ([]string, []string, error) {
	targets := parseCSV(viper.GetString("TARGETS"))
	legacyDomains := parseCSV(viper.GetString("DOMAINS"))
	legacyHostnames := parseCSV(viper.GetString("HOSTNAMES"))

	if len(legacyDomains) > 0 || len(legacyHostnames) > 0 {
		log.Warn(
			"DNSWATCHER_DOMAINS and DNSWATCHER_HOSTNAMES are deprecated; use DNSWATCHER_TARGETS instead",
		)
	}

	var domains, hostnames []string

	if len(targets) > 0 {
		var err error

		domains, hostnames, err = ClassifyTargets(targets)
		if err != nil {
			return nil, nil, err
		}
	}

	domains = mergeUnique(domains, legacyDomains)
	hostnames = mergeUnique(hostnames, legacyHostnames)

	return domains, hostnames, nil
}

// mergeUnique appends items from b into a, skipping duplicates.
func mergeUnique(a, b []string) []string {
	seen := make(map[string]bool, len(a))
	for _, v := range a {
		seen[v] = true
	}

	for _, v := range b {
		if !seen[v] {
			a = append(a, v)
			seen[v] = true
		}
	}

	return a
}

// StatePath returns the full path to the state JSON file.
func (c *Config) StatePath() string {
	return c.DataDir + "/state.json"
}