feat: backend service

backend/internal/server/middleware/geocounter/geocounter.go

@@ -0,0 +1,58 @@
+// Package geocounter exposes the gin middleware that records
+// `(user_id, country)` counters for every authenticated user-surface
+// request. The middleware sits one layer below `userid.Middleware` in
+// the route chain: it relies on the parsed user id already being on
+// the request context.
+//
+// The middleware never blocks: the underlying counter implementation
+// looks up the country synchronously (mmap read) and dispatches the
+// database upsert to a fire-and-forget goroutine. Errors from the
+// asynchronous path are logged inside the geo service, never surfaced
+// to the response.
+package geocounter
+
+import (
+	"context"
+
+	"galaxy/backend/internal/server/clientip"
+	"galaxy/backend/internal/server/middleware/userid"
+
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+)
+
+// Service is the narrow contract the middleware needs from the geo
+// package. It is satisfied by `*geo.Service` directly; tests inject a
+// recording stub. A nil Service is allowed and disables the
+// middleware's side effect.
+type Service interface {
+	IncrementCounterAsync(ctx context.Context, userID uuid.UUID, sourceIP string)
+}
+
+// Middleware returns a gin handler that, after the wrapped handler
+// chain has run, dispatches an `IncrementCounterAsync` call for the
+// authenticated user and the originating IP. svc may be nil, in which
+// case the middleware is a no-op pass-through.
+//
+// The middleware reads the user id from the request context populated
+// by `userid.Middleware`; routes that mount this middleware without
+// `userid.Middleware` ahead of it will silently skip the increment
+// because the user id is absent.
+func Middleware(svc Service) gin.HandlerFunc {
+	return func(c *gin.Context) {
+		c.Next()
+
+		if svc == nil {
+			return
+		}
+		userID, ok := userid.FromContext(c.Request.Context())
+		if !ok || userID == uuid.Nil {
+			return
+		}
+		ip := clientip.ExtractSourceIP(c)
+		if ip == "" {
+			return
+		}
+		svc.IncrementCounterAsync(c.Request.Context(), userID, ip)
+	}
+}