// Package server wires the backend's HTTP listener: the gin engine, its route
// groups, the per-request telemetry middleware and the start/stop lifecycle.
//
// The /api/v1 route groups (public, user, internal, admin) are created here so
// later stages attach their endpoints to a stable structure; the /user group
// requires the X-User-ID identity header. The probes /healthz (liveness) and
// /readyz (database + session-cache readiness) are unauthenticated.
package server

import (
	"context"
	"database/sql"
	"errors"
	"net/http"
	"time"

	"github.com/gin-gonic/gin"
	"go.uber.org/zap"

	"scrabble/backend/internal/account"
	"scrabble/backend/internal/game"
	"scrabble/backend/internal/lobby"
	"scrabble/backend/internal/session"
	"scrabble/backend/internal/social"
	"scrabble/backend/internal/telemetry"
)

// shutdownTimeout bounds how long Run waits for in-flight requests to finish
// during a graceful shutdown.
const shutdownTimeout = 10 * time.Second

// defaultPingTimeout bounds the /readyz database ping when Deps.PingTimeout is
// not set.
const defaultPingTimeout = 5 * time.Second

// Deps carries the runtime dependencies the HTTP layer needs.
type Deps struct {
	// Logger receives lifecycle, request and readiness diagnostics.
	Logger *zap.Logger
	// DB backs the /readyz database ping. A nil DB skips the database check.
	DB *sql.DB
	// PingTimeout bounds the /readyz database ping.
	PingTimeout time.Duration
	// SessionsReady reports whether the session cache has been warmed. A nil
	// func skips the session-readiness check.
	SessionsReady func() bool
	// Sessions, Accounts and Games are the identity, account and game-domain
	// services the Stage 6 REST handlers route to.
	Sessions *session.Service
	Accounts *account.Store
	Games    *game.Service
	// Social, Matchmaker, Invitations and Emails are the Stage 4 domain services
	// the Stage 6 REST handlers route to.
	Social      *social.Service
	Matchmaker  *lobby.Matchmaker
	Invitations *lobby.InvitationService
	Emails      *account.EmailService
}

// Server owns the gin engine, the underlying HTTP server and the readiness
// dependencies.
type Server struct {
	log           *zap.Logger
	http          *http.Server
	db            *sql.DB
	pingTimeout   time.Duration
	sessionsReady func() bool

	sessions    *session.Service
	accounts    *account.Store
	games       *game.Service
	social      *social.Service
	matchmaker  *lobby.Matchmaker
	invitations *lobby.InvitationService
	emails      *account.EmailService

	public   *gin.RouterGroup
	user     *gin.RouterGroup
	internal *gin.RouterGroup
	admin    *gin.RouterGroup
}

// New returns a Server that will listen on addr. It installs the recovery and
// telemetry middleware, the infrastructure probes, and the /api/v1 route groups.
func New(addr string, deps Deps) *Server {
	log := deps.Logger
	if log == nil {
		log = zap.NewNop()
	}
	pingTimeout := deps.PingTimeout
	if pingTimeout <= 0 {
		pingTimeout = defaultPingTimeout
	}

	gin.SetMode(gin.ReleaseMode)
	engine := gin.New()
	engine.Use(gin.Recovery())
	engine.Use(telemetry.Middleware(log))

	s := &Server{
		log:           log,
		db:            deps.DB,
		pingTimeout:   pingTimeout,
		sessionsReady: deps.SessionsReady,
		sessions:      deps.Sessions,
		accounts:      deps.Accounts,
		games:         deps.Games,
		social:        deps.Social,
		matchmaker:    deps.Matchmaker,
		invitations:   deps.Invitations,
		emails:        deps.Emails,
		http:          &http.Server{Addr: addr, Handler: engine},
	}
	s.registerProbes(engine)
	s.registerAPIGroups(engine)
	s.registerRoutes()
	return s
}

// registerProbes installs the unauthenticated infrastructure probes: /healthz
// reports process liveness and /readyz reports readiness to serve traffic
// (database reachable and session cache warmed).
func (s *Server) registerProbes(engine *gin.Engine) {
	engine.GET("/healthz", func(c *gin.Context) { c.String(http.StatusOK, "ok") })
	engine.GET("/readyz", s.readyz)
}

// readyz reports 200 only when the database answers a bounded ping and the
// session cache is warmed; otherwise 503.
func (s *Server) readyz(c *gin.Context) {
	if s.db != nil {
		ctx, cancel := context.WithTimeout(c.Request.Context(), s.pingTimeout)
		defer cancel()
		if err := s.db.PingContext(ctx); err != nil {
			s.log.Warn("readiness: database ping failed", zap.Error(err))
			c.String(http.StatusServiceUnavailable, "database unavailable")
			return
		}
	}
	if s.sessionsReady != nil && !s.sessionsReady() {
		c.String(http.StatusServiceUnavailable, "sessions not ready")
		return
	}
	c.String(http.StatusOK, "ok")
}

// registerAPIGroups wires the /api/v1 route groups. They are populated by the
// stages that add their first endpoint; the /user group requires X-User-ID,
// which the gateway injects after resolving a session.
func (s *Server) registerAPIGroups(engine *gin.Engine) {
	v1 := engine.Group("/api/v1")
	s.public = v1.Group("/public")
	s.user = v1.Group("/user")
	s.user.Use(RequireUserID())
	s.internal = v1.Group("/internal")
	s.admin = v1.Group("/admin")
}

// PublicGroup returns the unauthenticated public route group.
func (s *Server) PublicGroup() *gin.RouterGroup { return s.public }

// UserGroup returns the authenticated user route group (requires X-User-ID).
func (s *Server) UserGroup() *gin.RouterGroup { return s.user }

// InternalGroup returns the gateway-facing internal route group.
func (s *Server) InternalGroup() *gin.RouterGroup { return s.internal }

// AdminGroup returns the admin route group (authenticated at the gateway).
func (s *Server) AdminGroup() *gin.RouterGroup { return s.admin }

// Social returns the social domain service for the handlers added in Stage 6.
func (s *Server) Social() *social.Service { return s.social }

// Matchmaker returns the in-memory matchmaking pool for the Stage 6 handlers.
func (s *Server) Matchmaker() *lobby.Matchmaker { return s.matchmaker }

// Invitations returns the friend-game invitation service for the Stage 6 handlers.
func (s *Server) Invitations() *lobby.InvitationService { return s.invitations }

// Emails returns the email confirm-code service for the Stage 6 handlers.
func (s *Server) Emails() *account.EmailService { return s.emails }

// Handler returns the underlying HTTP handler. It lets tests drive the server
// without binding a socket and lets later stages compose the backend behind
// another listener.
func (s *Server) Handler() http.Handler { return s.http.Handler }

// Run starts the listener and blocks until ctx is cancelled, then shuts the
// server down gracefully within shutdownTimeout. It returns the first error
// that is not the expected http.ErrServerClosed.
func (s *Server) Run(ctx context.Context) error {
	errc := make(chan error, 1)
	go func() {
		s.log.Info("http listener starting", zap.String("addr", s.http.Addr))
		errc <- s.http.ListenAndServe()
	}()

	select {
	case err := <-errc:
		if errors.Is(err, http.ErrServerClosed) {
			return nil
		}
		return err
	case <-ctx.Done():
		s.log.Info("http listener stopping")
		shutdownCtx, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
		defer cancel()
		return s.http.Shutdown(shutdownCtx)
	}
}