feat: authsession service

authsession/internal/domain/sessionlimit/model.go

@@ -0,0 +1,89 @@
+// Package sessionlimit defines the domain decision shape used for active
+// device-session limit evaluation.
+package sessionlimit
+
+import (
+	"errors"
+	"fmt"
+)
+
+// Kind identifies the coarse outcome of evaluating the active-session limit.
+type Kind string
+
+const (
+	// KindDisabled reports that no configured limit is currently active.
+	KindDisabled Kind = "disabled"
+
+	// KindAllowed reports that creating the next session is allowed.
+	KindAllowed Kind = "allowed"
+
+	// KindExceeded reports that creating the next session would exceed the
+	// configured limit.
+	KindExceeded Kind = "exceeded"
+)
+
+// IsKnown reports whether Kind is one of the session-limit outcomes supported
+// by the current domain model.
+func (k Kind) IsKnown() bool {
+	switch k {
+	case KindDisabled, KindAllowed, KindExceeded:
+		return true
+	default:
+		return false
+	}
+}
+
+// Decision stores the result of evaluating one possible next session creation.
+type Decision struct {
+	// Kind reports the coarse decision outcome.
+	Kind Kind
+
+	// ConfiguredLimit stores the active configured limit when one exists.
+	ConfiguredLimit *int
+
+	// ActiveSessionCount stores the current active-session count before create.
+	ActiveSessionCount int
+
+	// NextSessionCount stores the count that would exist after creating the next
+	// session.
+	NextSessionCount int
+}
+
+// Validate reports whether Decision satisfies the Stage-2 structural
+// invariants.
+func (d Decision) Validate() error {
+	if !d.Kind.IsKnown() {
+		return fmt.Errorf("session-limit decision kind %q is unsupported", d.Kind)
+	}
+	if d.ActiveSessionCount < 0 {
+		return errors.New("session-limit active session count must not be negative")
+	}
+	if d.NextSessionCount < 0 {
+		return errors.New("session-limit next session count must not be negative")
+	}
+	if d.NextSessionCount != d.ActiveSessionCount+1 {
+		return errors.New("session-limit next session count must equal active session count plus one")
+	}
+
+	switch d.Kind {
+	case KindDisabled:
+		if d.ConfiguredLimit != nil {
+			return errors.New("disabled session-limit decision must not contain configured limit")
+		}
+	case KindAllowed, KindExceeded:
+		if d.ConfiguredLimit == nil {
+			return errors.New("limited session-limit decision must contain configured limit")
+		}
+		if *d.ConfiguredLimit <= 0 {
+			return errors.New("session-limit configured limit must be positive")
+		}
+		if d.Kind == KindAllowed && d.NextSessionCount > *d.ConfiguredLimit {
+			return errors.New("allowed session-limit decision must not exceed configured limit")
+		}
+		if d.Kind == KindExceeded && d.NextSessionCount <= *d.ConfiguredLimit {
+			return errors.New("exceeded session-limit decision must be above configured limit")
+		}
+	}
+
+	return nil
+}