// Package connectsrv implements the public Connect edge service over h2c. Execute
// rate-limits, authenticates (resolving the Authorization bearer token to a user
// id for non-auth operations), and dispatches to the transcode registry; the
// domain outcome is carried back in the ExecuteResponse result_code. Subscribe
// bridges the gateway push hub to a client server-stream with a keep-alive
// heartbeat.
package connectsrv

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

	"connectrpc.com/connect"
	"go.uber.org/zap"
	"golang.org/x/net/http2"
	"golang.org/x/net/http2/h2c"

	"scrabble/gateway/internal/config"
	"scrabble/gateway/internal/push"
	"scrabble/gateway/internal/ratelimit"
	"scrabble/gateway/internal/session"
	"scrabble/gateway/internal/transcode"
	edgev1 "scrabble/gateway/proto/edge/v1"
	"scrabble/gateway/proto/edge/v1/edgev1connect"
)

// heartbeatKind is the live-stream keep-alive event kind.
const heartbeatKind = "heartbeat"

// Server implements edgev1connect.GatewayHandler.
type Server struct {
	registry   *transcode.Registry
	sessions   *session.Cache
	limiter    *ratelimit.Limiter
	hub        *push.Hub
	heartbeat  time.Duration
	log        *zap.Logger
	adminProxy http.Handler

	publicPolicy ratelimit.Policy
	userPolicy   ratelimit.Policy
	emailPolicy  ratelimit.Policy
}

// Deps carries the Server's dependencies.
type Deps struct {
	Registry   *transcode.Registry
	Sessions   *session.Cache
	Limiter    *ratelimit.Limiter
	Hub        *push.Hub
	RateLimit  config.RateLimitConfig
	Heartbeat  time.Duration
	Logger     *zap.Logger
	AdminProxy http.Handler
}

// NewServer constructs the edge service.
func NewServer(d Deps) *Server {
	log := d.Logger
	if log == nil {
		log = zap.NewNop()
	}
	return &Server{
		registry:     d.Registry,
		sessions:     d.Sessions,
		limiter:      d.Limiter,
		hub:          d.Hub,
		heartbeat:    d.Heartbeat,
		log:          log,
		adminProxy:   d.AdminProxy,
		publicPolicy: ratelimit.PerMinute(d.RateLimit.PublicPerMinute, d.RateLimit.PublicBurst),
		userPolicy:   ratelimit.PerMinute(d.RateLimit.UserPerMinute, d.RateLimit.UserBurst),
		emailPolicy:  ratelimit.Per(d.RateLimit.EmailPer10Min, 10*time.Minute, d.RateLimit.EmailBurst),
	}
}

// HTTPHandler returns the h2c-wrapped Connect handler ready to serve.
func (s *Server) HTTPHandler() http.Handler {
	mux := http.NewServeMux()
	path, h := edgev1connect.NewGatewayHandler(s)
	mux.Handle(path, h)
	if s.adminProxy != nil {
		// The admin console (backend /_gm) is served on the public listener behind
		// the proxy's Basic-Auth, mounted below the h2c wrap so the Connect edge keeps
		// working over h2c (docs/ARCHITECTURE.md §12).
		mux.Handle("/_gm/", s.adminProxy)
	}
	return h2c.NewHandler(mux, &http2.Server{})
}

// Execute runs one unary operation. Domain failures are returned in the envelope
// (result_code != "ok", HTTP 200); only edge failures (rate limit, missing
// session, unknown type, internal) become Connect errors.
func (s *Server) Execute(ctx context.Context, req *connect.Request[edgev1.ExecuteRequest]) (*connect.Response[edgev1.ExecuteResponse], error) {
	msgType := req.Msg.GetMessageType()
	op, ok := s.registry.Lookup(msgType)
	if !ok {
		return nil, connect.NewError(connect.CodeNotFound, errUnknownMessageType(msgType))
	}
	clientIP := peerIP(req.Peer().Addr, req.Header())

	tr := transcode.Request{Payload: req.Msg.GetPayload(), ClientIP: clientIP}
	if op.Auth {
		uid, err := s.resolve(ctx, req.Header())
		if err != nil {
			return nil, err
		}
		if !s.limiter.Allow("user:"+uid, s.userPolicy) {
			return nil, connect.NewError(connect.CodeResourceExhausted, errRateLimited)
		}
		tr.UserID = uid
	} else {
		if !s.limiter.Allow("ip:"+clientIP, s.publicPolicy) {
			return nil, connect.NewError(connect.CodeResourceExhausted, errRateLimited)
		}
		if op.Email && !s.limiter.Allow("email:"+clientIP, s.emailPolicy) {
			return nil, connect.NewError(connect.CodeResourceExhausted, errRateLimited)
		}
	}

	payload, err := op.Handler(ctx, tr)
	if err != nil {
		if code, domain := transcode.DomainCode(err); domain {
			return connect.NewResponse(&edgev1.ExecuteResponse{
				RequestId:  req.Msg.GetRequestId(),
				ResultCode: code,
			}), nil
		}
		s.log.Error("execute failed", zap.String("message_type", msgType), zap.Error(err))
		return nil, connect.NewError(connect.CodeInternal, errInternal)
	}
	return connect.NewResponse(&edgev1.ExecuteResponse{
		RequestId:  req.Msg.GetRequestId(),
		ResultCode: "ok",
		Payload:    payload,
	}), nil
}

// Subscribe streams the authenticated user's live events with a keep-alive
// heartbeat until the client disconnects.
func (s *Server) Subscribe(ctx context.Context, req *connect.Request[edgev1.SubscribeRequest], stream *connect.ServerStream[edgev1.Event]) error {
	uid, err := s.resolve(ctx, req.Header())
	if err != nil {
		return err
	}
	if !s.limiter.Allow("user:"+uid, s.userPolicy) {
		return connect.NewError(connect.CodeResourceExhausted, errRateLimited)
	}

	events, cancel := s.hub.Subscribe(uid)
	defer cancel()

	ticker := time.NewTicker(s.heartbeat)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return nil
		case <-ticker.C:
			if err := stream.Send(&edgev1.Event{Kind: heartbeatKind}); err != nil {
				return err
			}
		case e, ok := <-events:
			if !ok {
				return nil
			}
			if err := stream.Send(&edgev1.Event{Kind: e.Kind, Payload: e.Payload, EventId: e.EventID}); err != nil {
				return err
			}
		}
	}
}

// resolve extracts and resolves the Authorization bearer token to an account id,
// returning a Connect Unauthenticated error when it is missing or unknown.
func (s *Server) resolve(ctx context.Context, h http.Header) (string, error) {
	token := bearerToken(h.Get("Authorization"))
	if token == "" {
		return "", connect.NewError(connect.CodeUnauthenticated, errMissingToken)
	}
	uid, err := s.sessions.Resolve(ctx, token)
	if err != nil {
		return "", connect.NewError(connect.CodeUnauthenticated, errInvalidSession)
	}
	return uid, nil
}

// bearerToken extracts the token from an "Authorization: Bearer <token>" header,
// tolerating a bare token for convenience.
func bearerToken(header string) string {
	header = strings.TrimSpace(header)
	if header == "" {
		return ""
	}
	if rest, ok := strings.CutPrefix(header, "Bearer "); ok {
		return strings.TrimSpace(rest)
	}
	return header
}

// peerIP prefers the X-Forwarded-For client hop, falling back to the connection
// peer address (host part).
func peerIP(peerAddr string, h http.Header) string {
	if xff := h.Get("X-Forwarded-For"); xff != "" {
		if i := strings.IndexByte(xff, ','); i >= 0 {
			return strings.TrimSpace(xff[:i])
		}
		return strings.TrimSpace(xff)
	}
	if host, _, err := net.SplitHostPort(peerAddr); err == nil {
		return host
	}
	return peerAddr
}