feat: authsession service

authsession/internal/service/shared/session_limit.go

@@ -0,0 +1,40 @@
+package shared
+
+import (
+	"fmt"
+
+	"galaxy/authsession/internal/domain/sessionlimit"
+	"galaxy/authsession/internal/ports"
+)
+
+// EvaluateSessionLimit evaluates the Stage-4 active-session creation decision
+// from the loaded configuration and current active-session count.
+func EvaluateSessionLimit(config ports.SessionLimitConfig, activeSessionCount int) (sessionlimit.Decision, error) {
+	if err := config.Validate(); err != nil {
+		return sessionlimit.Decision{}, InternalError(fmt.Errorf("evaluate session limit: %w", err))
+	}
+	if activeSessionCount < 0 {
+		return sessionlimit.Decision{}, InternalError(fmt.Errorf("evaluate session limit: active session count %d is negative", activeSessionCount))
+	}
+
+	decision := sessionlimit.Decision{
+		ActiveSessionCount: activeSessionCount,
+		NextSessionCount:   activeSessionCount + 1,
+	}
+
+	if config.ActiveSessionLimit == nil {
+		decision.Kind = sessionlimit.KindDisabled
+	} else {
+		decision.ConfiguredLimit = config.ActiveSessionLimit
+		if decision.NextSessionCount <= *config.ActiveSessionLimit {
+			decision.Kind = sessionlimit.KindAllowed
+		} else {
+			decision.Kind = sessionlimit.KindExceeded
+		}
+	}
+	if err := decision.Validate(); err != nil {
+		return sessionlimit.Decision{}, InternalError(fmt.Errorf("evaluate session limit: %w", err))
+	}
+
+	return decision, nil
+}