scrabble-game/gateway/internal/config/config.go

// Package config loads and validates the gateway's runtime configuration from
// the process environment. Every variable is prefixed GATEWAY_.
package config

import (
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"

	pkgtel "scrabble/pkg/telemetry"
)

// Config holds the gateway's runtime configuration.
type Config struct {
	// HTTPAddr is the public Connect/h2c listener address (host:port). It also
	// serves the admin console at /_gm when admin credentials are configured.
	HTTPAddr string
	// LogLevel is the zap log level: "debug", "info", "warn" or "error".
	LogLevel string
	// BackendHTTPURL is the base URL of the backend REST API (gateway -> backend).
	BackendHTTPURL string
	// BackendGRPCAddr is the backend push gRPC address the gateway subscribes to.
	BackendGRPCAddr string
	// BackendTimeout bounds a single backend REST call.
	BackendTimeout time.Duration
	// AdminUser and AdminPassword are the Basic-Auth credentials the gateway
	// checks before proxying admin traffic to the backend. Empty disables admin.
	AdminUser     string
	AdminPassword string
	// ConnectorAddr is the gRPC address of the Telegram connector side-service. The
	// gateway calls it to validate Mini App initData and to deliver out-of-app push.
	// Empty disables the telegram auth path and the out-of-app push channel.
	ConnectorAddr string
	// DefaultSupportedLanguages is the New Game variant gating set put on the Session
	// for non-platform logins (web / email / guest), which carry no service container
	// to declare one. The UI offers only variants in this set (en -> English; ru ->
	// Russian + Эрудит). Defaults to all of them; a deployment may narrow it.
	DefaultSupportedLanguages []string
	// SessionTTL bounds how long a resolved session stays cached; SessionCacheMax
	// caps the number of cached sessions.
	SessionTTL      time.Duration
	SessionCacheMax int
	// PushHeartbeatInterval is the idle keep-alive cadence on a client live stream.
	PushHeartbeatInterval time.Duration
	// MaxBodyBytes caps one inbound request body on the public listener and one
	// Connect message read; oversized requests are refused without buffering.
	MaxBodyBytes int
	// RateLimit configures the in-memory anti-abuse limiter.
	RateLimit RateLimitConfig
	// Telemetry configures the OpenTelemetry providers (shared bootstrap).
	Telemetry pkgtel.Config
}

// RateLimitConfig holds the token-bucket limits per class. Public and admin are
// keyed per client IP; the authenticated class is keyed per user id; the email
// sub-limit guards the costly email-code path per IP.
type RateLimitConfig struct {
	PublicPerMinute int
	PublicBurst     int
	UserPerMinute   int
	UserBurst       int
	AdminPerMinute  int
	AdminBurst      int
	EmailPer10Min   int
	EmailBurst      int
}

// Defaults applied when the corresponding environment variable is unset.
const (
	defaultHTTPAddr              = ":8081"
	defaultLogLevel              = "info"
	defaultBackendHTTPURL        = "http://localhost:8080"
	defaultBackendGRPCAddr       = "localhost:9090"
	defaultBackendTimeout        = 5 * time.Second
	defaultSessionTTL            = 10 * time.Minute
	defaultSessionCacheMax       = 50000
	defaultPushHeartbeatInterval = 10 * time.Second // under the ~15 s edge idle timeout (Stage 17)
	defaultServiceName           = "scrabble-gateway"
)

// DefaultMaxBodyBytes is the default request-body cap (GATEWAY_MAX_BODY_BYTES):
// 1 MiB — far above any legitimate edge payload (drafts and chat are a few KB)
// yet small enough to stop a cheap memory-amplification upload (R3).
const DefaultMaxBodyBytes = 1 << 20

// supportedLanguages is the set of game languages a service may declare for the
// New Game variant gating; defaultSupportedLanguages is the non-platform fallback.
var (
	supportedLanguages        = map[string]bool{"en": true, "ru": true}
	defaultSupportedLanguages = []string{"en", "ru"}
)

// DefaultRateLimit returns the built-in anti-abuse limits.
func DefaultRateLimit() RateLimitConfig {
	return RateLimitConfig{
		PublicPerMinute: 30, PublicBurst: 10,
		// Per-user (not per-IP): one user may run several devices, each holding a
		// Subscribe stream and reloading state on every live event, so the authenticated
		// budget is generous (a per-user cap cannot DoS the service). Raised in Stage 17
		// after multi-device play tripped the old 120/40.
		UserPerMinute: 300, UserBurst: 80,
		AdminPerMinute: 60, AdminBurst: 20,
		EmailPer10Min: 5, EmailBurst: 2,
	}
}

// Load reads the configuration from the environment, applies defaults, and
// validates the result.
func Load() (Config, error) {
	var err error
	c := Config{
		HTTPAddr:        envOr("GATEWAY_HTTP_ADDR", defaultHTTPAddr),
		LogLevel:        envOr("GATEWAY_LOG_LEVEL", defaultLogLevel),
		BackendHTTPURL:  envOr("GATEWAY_BACKEND_HTTP_URL", defaultBackendHTTPURL),
		BackendGRPCAddr: envOr("GATEWAY_BACKEND_GRPC_ADDR", defaultBackendGRPCAddr),
		AdminUser:       os.Getenv("GATEWAY_ADMIN_USER"),
		AdminPassword:   os.Getenv("GATEWAY_ADMIN_PASSWORD"),
		ConnectorAddr:   os.Getenv("GATEWAY_CONNECTOR_ADDR"),
		SessionCacheMax: defaultSessionCacheMax,
		RateLimit:       DefaultRateLimit(),
	}
	tel := pkgtel.DefaultConfig(defaultServiceName)
	tel.ServiceName = envOr("GATEWAY_SERVICE_NAME", tel.ServiceName)
	tel.TracesExporter = envOr("GATEWAY_OTEL_TRACES_EXPORTER", tel.TracesExporter)
	tel.MetricsExporter = envOr("GATEWAY_OTEL_METRICS_EXPORTER", tel.MetricsExporter)
	c.Telemetry = tel
	if c.BackendTimeout, err = envDuration("GATEWAY_BACKEND_TIMEOUT", defaultBackendTimeout); err != nil {
		return Config{}, err
	}
	if c.SessionTTL, err = envDuration("GATEWAY_SESSION_TTL", defaultSessionTTL); err != nil {
		return Config{}, err
	}
	if c.SessionCacheMax, err = envInt("GATEWAY_SESSION_CACHE_MAX", defaultSessionCacheMax); err != nil {
		return Config{}, err
	}
	if c.PushHeartbeatInterval, err = envDuration("GATEWAY_PUSH_HEARTBEAT_INTERVAL", defaultPushHeartbeatInterval); err != nil {
		return Config{}, err
	}
	if c.MaxBodyBytes, err = envInt("GATEWAY_MAX_BODY_BYTES", DefaultMaxBodyBytes); err != nil {
		return Config{}, err
	}
	if c.DefaultSupportedLanguages, err = envLanguages("GATEWAY_DEFAULT_SUPPORTED_LANGUAGES", defaultSupportedLanguages); err != nil {
		return Config{}, err
	}
	if err := c.validate(); err != nil {
		return Config{}, err
	}
	return c, nil
}

// AdminEnabled reports whether the admin console proxy should be mounted (both
// Basic-Auth credentials are configured).
func (c Config) AdminEnabled() bool {
	return c.AdminUser != "" && c.AdminPassword != ""
}

// validate reports whether the configuration values are acceptable.
func (c Config) validate() error {
	switch c.LogLevel {
	case "debug", "info", "warn", "error":
	default:
		return fmt.Errorf("config: invalid GATEWAY_LOG_LEVEL %q", c.LogLevel)
	}
	if c.HTTPAddr == "" {
		return fmt.Errorf("config: GATEWAY_HTTP_ADDR must not be empty")
	}
	if c.BackendHTTPURL == "" {
		return fmt.Errorf("config: GATEWAY_BACKEND_HTTP_URL must not be empty")
	}
	if c.BackendGRPCAddr == "" {
		return fmt.Errorf("config: GATEWAY_BACKEND_GRPC_ADDR must not be empty")
	}
	if c.MaxBodyBytes <= 0 {
		return fmt.Errorf("config: GATEWAY_MAX_BODY_BYTES must be positive")
	}
	if err := c.Telemetry.Validate(); err != nil {
		return fmt.Errorf("config: %w", err)
	}
	return nil
}

// envOr returns the value of the environment variable named key, or fallback
// when the variable is unset or empty.
func envOr(key, fallback string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return fallback
}

// envLanguages parses a comma-separated language list (e.g. "en,ru") from the
// environment variable named key, returning fallback when it is unset. Every entry
// must be a supported language and the result must be non-empty.
func envLanguages(key string, fallback []string) ([]string, error) {
	raw := strings.TrimSpace(os.Getenv(key))
	if raw == "" {
		return fallback, nil
	}
	var out []string
	for part := range strings.SplitSeq(raw, ",") {
		lang := strings.ToLower(strings.TrimSpace(part))
		if lang == "" {
			continue
		}
		if !supportedLanguages[lang] {
			return nil, fmt.Errorf("config: %s: unsupported language %q", key, lang)
		}
		out = append(out, lang)
	}
	if len(out) == 0 {
		return nil, fmt.Errorf("config: %s must list at least one language", key)
	}
	return out, nil
}

// envInt parses the environment variable named key as an int, returning fallback
// when it is unset and an error when it is set but malformed.
func envInt(key string, fallback int) (int, error) {
	v := os.Getenv(key)
	if v == "" {
		return fallback, nil
	}
	n, err := strconv.Atoi(v)
	if err != nil {
		return 0, fmt.Errorf("config: %s: %w", key, err)
	}
	return n, nil
}

// envDuration parses the environment variable named key as a Go duration,
// returning fallback when it is unset and an error when it is set but malformed.
func envDuration(key string, fallback time.Duration) (time.Duration, error) {
	v := os.Getenv(key)
	if v == "" {
		return fallback, nil
	}
	d, err := time.ParseDuration(v)
	if err != nil {
		return 0, fmt.Errorf("config: %s: %w", key, err)
	}
	return d, nil
}