package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"strings"
	"time"

	"github.com/gofiber/fiber/v3"
	"github.com/gofiber/fiber/v3/middleware/adaptor"
	redisv9 "github.com/redis/go-redis/v9"

	gconfig "knowfoolery/backend/services/gateway-service/internal/infra/config"
	"knowfoolery/backend/services/gateway-service/internal/infra/proxy"
	httpapi "knowfoolery/backend/services/gateway-service/internal/interfaces/http"
	"knowfoolery/backend/services/gateway-service/internal/interfaces/http/middleware"
	"knowfoolery/backend/shared/infra/auth/zitadel"
	"knowfoolery/backend/shared/infra/observability/logging"
	sharedmetrics "knowfoolery/backend/shared/infra/observability/metrics"
	"knowfoolery/backend/shared/infra/observability/tracing"
	"knowfoolery/backend/shared/infra/utils/serviceboot"
)

func main() {
	cfg := gconfig.FromEnv()

	logger := logging.NewLogger(cfg.Logging)
	if err := cfg.Upstreams.Validate(); err != nil {
		logger.WithError(err).Fatal("invalid gateway upstream configuration")
	}

	sharedmetrics.NewMetrics(cfg.Metrics)

	tracer, err := tracing.NewTracer(cfg.Tracing)
	if err != nil {
		logger.Fatal("failed to initialize tracer")
	}
	defer func() {
		_ = tracer.Shutdown(context.Background())
	}()

	redisClient := initRedis(cfg, logger)
	if redisClient != nil {
		defer func() { _ = redisClient.Close() }()
	}

	bootCfg := serviceboot.Config{
		AppName:     cfg.AppName,
		ServiceSlug: "gateway",
		PortEnv:     "GATEWAY_INTERNAL_PORT",
		DefaultPort: cfg.Port,
	}
	app := serviceboot.NewFiberApp(bootCfg)
	serviceboot.RegisterHealth(app, bootCfg.ServiceSlug)
	serviceboot.RegisterReadiness(app, 2*time.Second, readinessChecks(cfg, redisClient)...)
	app.Get("/metrics", adaptor.HTTPHandler(sharedmetrics.Handler()))

	app.Use(middleware.RequestContext(logger))
	app.Use(middleware.SecurityHeaders(cfg.Security))
	app.Use(middleware.CORS(cfg.CORS))

	authMiddleware := buildAuthMiddleware(cfg)
	rateLimitMiddleware := middleware.RateLimitMiddleware(redisClient, cfg.Rate, cfg.PublicPrefix, logger)

	httpapi.RegisterRoutes(app, httpapi.Options{
		PublicPrefix:        cfg.PublicPrefix,
		Upstreams:           cfg.Upstreams,
		Proxy:               proxy.New(cfg.UpstreamTimeout, logger),
		AuthMiddleware:      authMiddleware,
		RateLimitMiddleware: rateLimitMiddleware,
	})

	addr := serviceboot.ListenAddress(bootCfg.PortEnv, bootCfg.DefaultPort)
	log.Fatal(serviceboot.Run(app, addr))
}

func initRedis(cfg gconfig.Config, logger *logging.Logger) *redisv9.Client {
	opt := &redisv9.Options{
		Addr:         cfg.Redis.Addr(),
		Password:     cfg.Redis.Password,
		DB:           cfg.Redis.DB,
		PoolSize:     cfg.Redis.PoolSize,
		MinIdleConns: cfg.Redis.MinIdleConns,
		DialTimeout:  cfg.Redis.DialTimeout,
		ReadTimeout:  cfg.Redis.ReadTimeout,
		WriteTimeout: cfg.Redis.WriteTimeout,
	}

	client := redisv9.NewClient(opt)
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	if err := client.Ping(ctx).Err(); err != nil {
		logger.WithError(err).Warn("redis unavailable; rate limiting running in degraded fail-open mode")
		_ = client.Close()
		return nil
	}

	return client
}

func readinessChecks(cfg gconfig.Config, redisClient *redisv9.Client) []serviceboot.ReadyCheck {
	checks := []serviceboot.ReadyCheck{
		{
			Name:     "redis",
			Required: false,
			Probe: func(ctx context.Context) error {
				if redisClient == nil {
					return fmt.Errorf("redis unavailable")
				}
				return redisClient.Ping(ctx).Err()
			},
		},
		{
			Name:     "game-session",
			Required: false,
			Probe:    makeHealthProbe(cfg.Upstreams.GameSession, cfg.UpstreamTimeout),
		},
		{
			Name:     "question-bank",
			Required: false,
			Probe:    makeHealthProbe(cfg.Upstreams.QuestionBank, cfg.UpstreamTimeout),
		},
		{
			Name:     "user",
			Required: false,
			Probe:    makeHealthProbe(cfg.Upstreams.User, cfg.UpstreamTimeout),
		},
		{
			Name:     "leaderboard",
			Required: false,
			Probe:    makeHealthProbe(cfg.Upstreams.Leaderboard, cfg.UpstreamTimeout),
		},
		{
			Name:     "admin",
			Required: false,
			Probe:    makeHealthProbe(cfg.Upstreams.Admin, cfg.UpstreamTimeout),
		},
	}
	return checks
}

func makeHealthProbe(baseURL string, timeout time.Duration) func(ctx context.Context) error {
	if timeout <= 0 {
		timeout = 2 * time.Second
	}

	return func(ctx context.Context) error {
		healthURL := strings.TrimRight(baseURL, "/") + "/health"
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, healthURL, nil)
		if err != nil {
			return err
		}

		client := &http.Client{Timeout: timeout}
		resp, err := client.Do(req)
		if err != nil {
			return err
		}
		defer resp.Body.Close()

		if resp.StatusCode >= 400 {
			return fmt.Errorf("upstream returned %d", resp.StatusCode)
		}
		return nil
	}
}

func buildAuthMiddleware(cfg gconfig.Config) fiber.Handler {
	skipPaths := []string{
		"/health",
		"/ready",
		"/metrics",
		cfg.PublicPrefix + "/questions",
		cfg.PublicPrefix + "/leaderboard/top10",
		cfg.PublicPrefix + "/leaderboard/stats",
		cfg.PublicPrefix + "/admin/auth",
		cfg.PublicPrefix + "/users/register",
		cfg.PublicPrefix + "/users/verify-email",
	}

	return zitadel.BuildJWTMiddleware(zitadel.MiddlewareFactoryConfig{
		BaseURL:      cfg.ZitadelBaseURL,
		ClientID:     cfg.ZitadelClientID,
		ClientSecret: cfg.ZitadelSecret,
		Issuer:       cfg.ZitadelIssuer,
		Audience:     cfg.ZitadelAudience,
		RequiredClaims: []string{
			"sub",
		},
		AdminEndpoints: []string{cfg.PublicPrefix + "/admin"},
		SkipPaths:      skipPaths,
		Timeout:        10 * time.Second,
	})
}