fix(rpn): complete DIP for MetricRegistry — use MetricReader/MetricWriter interfaces (task ek)

6 files changed, 33 insertions, 17 deletions

diff --git a/internal/rpn/metric_registry.go b/internal/rpn/metric_registry.go
index a221e56..1aed264 100644
--- a/internal/rpn/metric_registry.go
+++ b/internal/rpn/metric_registry.go
@@ -28,6 +28,14 @@ type MetricReader interface {
 	ListByCategory(cat Category) []*Metric
 }
 
+// MetricWriter defines the write operations on a metric registry.
+type MetricWriter interface {
+	Register(m *Metric)
+	RegisterAlias(alias, canonicalName string)
+	Unregister(name string) error
+	MarkExactMatch(names ...string)
+}
+
 // Global registry instance.
 var defaultRegistry *MetricRegistry
 var registryOnce sync.Once
diff --git a/internal/rpn/operations.go b/internal/rpn/operations.go
index f79457c..989ce87 100644
--- a/internal/rpn/operations.go
+++ b/internal/rpn/operations.go
@@ -13,7 +13,7 @@ type Operations struct {
 	consts         ConstantsProvider
 	mode           CalculationMode
 	prefixMode     PrefixMode
-	metricRegistry *MetricRegistry
+	metricRegistry MetricReader
 	mu             sync.RWMutex
 }
 
@@ -38,8 +38,8 @@ var (
 // NewOperations creates a new Operations instance with the given variable store.
 // Does not create a ConstantsProvider internally; caller must use SetConstants.
 // If no registry is provided, defaults to the global MetricRegistry.
-func NewOperations(vars VariableStore, reg ...*MetricRegistry) *Operations {
-	r := GetMetricRegistry()
+func NewOperations(vars VariableStore, reg ...MetricReader) *Operations {
+	r := MetricReader(GetMetricRegistry())
 	if len(reg) > 0 && reg[0] != nil {
 		r = reg[0]
 	}
diff --git a/internal/rpn/operations_arithmetic.go b/internal/rpn/operations_arithmetic.go
index 1c4252c..4468edb 100644
--- a/internal/rpn/operations_arithmetic.go
+++ b/internal/rpn/operations_arithmetic.go
@@ -24,7 +24,7 @@ func (o *Operations) binaryMetricOp(
 	op string,
 	compatCheck func(*Metric, *Metric) error,
 	compute func(float64, float64) float64,
-	resultMetricFn func(*MetricRegistry, *Metric, *Metric) (*Metric, error),
+	resultMetricFn func(MetricReader, *Metric, *Metric) (*Metric, error),
 	preChecks ...func(StackValue) error,
 ) error {
 	a, b, err := popTwo(stack, op)
@@ -85,7 +85,7 @@ func (o *Operations) Add(stack *Stack) error {
 			return nil
 		},
 		func(a, b float64) float64 { return a + b },
-		func(reg *MetricRegistry, aM, bM *Metric) (*Metric, error) {
+		func(reg MetricReader, aM, bM *Metric) (*Metric, error) {
 			return compatibleMetric(reg, aM, bM), nil
 		},
 	)
@@ -102,7 +102,7 @@ func (o *Operations) Subtract(stack *Stack) error {
 			return nil
 		},
 		func(a, b float64) float64 { return a - b },
-		func(reg *MetricRegistry, aM, bM *Metric) (*Metric, error) {
+		func(reg MetricReader, aM, bM *Metric) (*Metric, error) {
 			return compatibleMetric(reg, aM, bM), nil
 		},
 	)
diff --git a/internal/rpn/operations_metric.go b/internal/rpn/operations_metric.go
index 64cce98..b621085 100644
--- a/internal/rpn/operations_metric.go
+++ b/internal/rpn/operations_metric.go
@@ -6,7 +6,7 @@ package rpn
 import "fmt"
 
 // resolveMetric returns the metric for a StackValue, defaulting to Cool if nil.
-func resolveMetric(reg *MetricRegistry, n StackValue) (*Metric, error) {
+func resolveMetric(reg MetricReader, n StackValue) (*Metric, error) {
 	m := n.Metric()
 	if m == nil {
 		var ok bool
@@ -59,7 +59,7 @@ func categoriesCompatible(a, b *Metric) bool {
 }
 
 // compatibleMetric returns the resulting metric for + and - operations.
-func compatibleMetric(reg *MetricRegistry, a, b *Metric) *Metric {
+func compatibleMetric(reg MetricReader, a, b *Metric) *Metric {
 	return resultMetricForAdd([]*Metric{a, b})
 }
 
@@ -73,7 +73,7 @@ func compatibleMetric(reg *MetricRegistry, a, b *Metric) *Metric {
 // NOT by 1 (base units).
 //
 // Returns the converted float64 value in base units.
-func convertToBase(reg *MetricRegistry, n StackValue, mode PrefixMode, resultMetric *Metric) (float64, error) {
+func convertToBase(reg MetricReader, n StackValue, mode PrefixMode, resultMetric *Metric) (float64, error) {
 	nv, ok := n.(NumericValue)
 	if !ok {
 		return 0, fmt.Errorf("convertToBase: value %q is not numeric", n)
@@ -95,7 +95,7 @@ func convertToBase(reg *MetricRegistry, n StackValue, mode PrefixMode, resultMet
 }
 
 // convertFromBase converts a base-unit value back to the given metric.
-func convertFromBase(reg *MetricRegistry, baseVal float64, m *Metric, mode PrefixMode) (float64, error) {
+func convertFromBase(reg MetricReader, baseVal float64, m *Metric, mode PrefixMode) (float64, error) {
 	if m == nil {
 		var err error
 		m, err = baseMetric(reg, "Cool")
@@ -116,7 +116,7 @@ var multiplicationInference = map[[2]Category]string{
 }
 
 // resultMetricForMul computes the resulting metric for multiplication.
-func resultMetricForMul(reg *MetricRegistry, a, b *Metric) (*Metric, error) {
+func resultMetricForMul(reg MetricReader, a, b *Metric) (*Metric, error) {
 	if a == nil || a.Category == Universal {
 		if b == nil {
 			return baseMetric(reg, "Cool")
@@ -141,7 +141,7 @@ var divisionInference = map[[2]Category]string{
 }
 
 // resultMetricForDiv computes the resulting metric for division.
-func resultMetricForDiv(reg *MetricRegistry, a, b *Metric) (*Metric, error) {
+func resultMetricForDiv(reg MetricReader, a, b *Metric) (*Metric, error) {
 	if a == nil && b == nil {
 		return baseMetric(reg, "Cool")
 	}
@@ -179,7 +179,7 @@ func metricError(op string, a, b *Metric) error {
 }
 
 // coolMetric returns the Cool metric from the registry.
-func coolMetric(reg *MetricRegistry) (*Metric, error) {
+func coolMetric(reg MetricReader) (*Metric, error) {
 	m, ok := reg.Find("Cool")
 	if !ok {
 		return nil, fmt.Errorf("metric registry missing Cool metric")
@@ -188,7 +188,7 @@ func coolMetric(reg *MetricRegistry) (*Metric, error) {
 }
 
 // baseMetric looks up a base metric from the registry.
-func baseMetric(reg *MetricRegistry, name string) (*Metric, error) {
+func baseMetric(reg MetricReader, name string) (*Metric, error) {
 	m, ok := reg.Find(name)
 	if !ok {
 		return nil, fmt.Errorf("metric registry missing base unit %q", name)
diff --git a/internal/rpn/operations_metric_cmd.go b/internal/rpn/operations_metric_cmd.go
index 255daed..370be98 100644
--- a/internal/rpn/operations_metric_cmd.go
+++ b/internal/rpn/operations_metric_cmd.go
@@ -150,11 +150,19 @@ func (o *Operations) CustomDefine(name string, factor float64, category string)
 		Factor:   func(PrefixMode) float64 { return factor },
 		IsCustom: true,
 	}
-	reg.Register(m)
+	writer, ok := reg.(MetricWriter)
+	if !ok {
+		return fmt.Errorf("metric registry does not support write operations")
+	}
+	writer.Register(m)
 	return nil
 }
 
 // CustomUndefine removes a custom metric.
 func (o *Operations) CustomUndefine(name string) error {
-	return o.metricRegistry.Unregister(name)
+	writer, ok := o.metricRegistry.(MetricWriter)
+	if !ok {
+		return fmt.Errorf("metric registry does not support write operations")
+	}
+	return writer.Unregister(name)
 }
diff --git a/internal/rpn/rpn_state.go b/internal/rpn/rpn_state.go
index adcf449..a42372a 100644
--- a/internal/rpn/rpn_state.go
+++ b/internal/rpn/rpn_state.go
@@ -22,7 +22,7 @@ type RPN struct {
 
 // NewRPN creates a new RPN parser and evaluator with the given variable store.
 // If no registry is provided, defaults to the global MetricRegistry.
-func NewRPN(vars VariableStore, reg ...*MetricRegistry) *RPN {
+func NewRPN(vars VariableStore, reg ...MetricReader) *RPN {
 	consts := NewConstants()
 	ops := NewOperations(vars, reg...)
 	ops.SetMode(FloatMode) // Set default mode