Refine API store capability boundaries

backend/internal/api/handlers.go

@@ -160,8 +160,9 @@ func (h *Handlers) Status(w http.ResponseWriter, r *http.Request) {
 	resp := statusResponse{Daemon: ds}
 
 	if h.store != nil {
+		var statsStore statsReader = h.store
 		currency := h.currentBaseCurrency(r.Context())
-		if stats, err := h.store.GetStats(r.Context(), currency); err == nil {
+		if stats, err := statsStore.GetStats(r.Context(), currency); err == nil {
 			resp.Stats = stats
 		}
 	}

backend/internal/api/handlers_config.go

@@ -61,6 +61,7 @@ func (h *Handlers) SetBaseCurrency(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusServiceUnavailable, "database not connected")
 		return
 	}
+	var configStore appConfigWriter = h.store
 	var body struct {
 		BaseCurrency string `json:"base_currency"`
 	}
@@ -79,7 +80,7 @@ func (h *Handlers) SetBaseCurrency(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 	}
-	if err := h.store.SetAppConfig(r.Context(), "base_currency", currency); err != nil {
+	if err := configStore.SetAppConfig(r.Context(), "base_currency", currency); err != nil {
 		h.logger.Error("set base currency", "error", err)
 		writeError(w, http.StatusInternalServerError, "failed to update base currency")
 		return
@@ -99,8 +100,9 @@ func (h *Handlers) GetScanInterval(w http.ResponseWriter, r *http.Request) {
 		writeError(w, http.StatusServiceUnavailable, "database not connected")
 		return
 	}
+	var configStore appConfigReader = h.store
 	val := strconv.Itoa(h.scanInterval)
-	if dbVal, err := h.store.GetAppConfig(r.Context(), "scan_interval"); err == nil && dbVal != "" {
+	if dbVal, err := configStore.GetAppConfig(r.Context(), "scan_interval"); err == nil && dbVal != "" {
 		val = dbVal
 	}
 	writeJSON(w, http.StatusOK, map[string]string{"scan_interval": val})
@@ -119,11 +121,12 @@ func (h *Handlers) GetScanInterval(w http.ResponseWriter, r *http.Request) {
 // @Failure 500 {object} ErrorResponse
 // @Failure 503 {object} ErrorResponse
 // @Router /config/scan-interval [put]
-func (h *Handlers) SetScanInterval(w http.ResponseWriter, r *http.Request) { //nolint:dupl // same shape as SetLookbackDays; different key and bounds
+func (h *Handlers) SetScanInterval(w http.ResponseWriter, r *http.Request) {
 	if h.store == nil {
 		writeError(w, http.StatusServiceUnavailable, "database not connected")
 		return
 	}
+	var configStore appConfigWriter = h.store
 	var body struct {
 		ScanInterval string `json:"scan_interval"`
 	}
@@ -136,7 +139,7 @@ func (h *Handlers) SetScanInterval(w http.ResponseWriter, r *http.Request) { //n
 		writeError(w, http.StatusBadRequest, "scan_interval must be an integer between 10 and 3600 seconds")
 		return
 	}
-	if err := h.store.SetAppConfig(r.Context(), "scan_interval", body.ScanInterval); err != nil {
+	if err := configStore.SetAppConfig(r.Context(), "scan_interval", body.ScanInterval); err != nil {
 		h.logger.Error("set scan interval", "error", err)
 		writeError(w, http.StatusInternalServerError, "failed to update scan interval")
 		return
@@ -176,7 +179,7 @@ func (h *Handlers) GetLookbackDays(w http.ResponseWriter, r *http.Request) {
 // @Failure 500 {object} ErrorResponse
 // @Failure 503 {object} ErrorResponse
 // @Router /config/lookback-days [put]
-func (h *Handlers) SetLookbackDays(w http.ResponseWriter, r *http.Request) { //nolint:dupl // same shape as SetScanInterval; different key and bounds
+func (h *Handlers) SetLookbackDays(w http.ResponseWriter, r *http.Request) {
 	if h.store == nil {
 		writeError(w, http.StatusServiceUnavailable, "database not connected")
 		return

backend/internal/api/http_helpers.go

@@ -14,7 +14,8 @@ import (
 // currentBaseCurrency returns the base currency from the DB, falling back to INR.
 func (h *Handlers) currentBaseCurrency(ctx context.Context) string {
 	if h.store != nil {
-		if val, err := h.store.GetAppConfig(ctx, "base_currency"); err == nil && val != "" {
+		var reader appConfigReader = h.store
+		if val, err := reader.GetAppConfig(ctx, "base_currency"); err == nil && val != "" {
 			return val
 		}
 	}

backend/internal/api/store_capabilities.go

@@ -0,0 +1,19 @@
+package api
+
+import (
+	"context"
+
+	"github.com/ArionMiles/expensor/backend/internal/store"
+)
+
+type appConfigReader interface {
+	GetAppConfig(ctx context.Context, key string) (string, error)
+}
+
+type appConfigWriter interface {
+	SetAppConfig(ctx context.Context, key, value string) error
+}
+
+type statsReader interface {
+	GetStats(ctx context.Context, baseCurrency string) (*store.Stats, error)
+}

backend/internal/api/store_capabilities_test.go

@@ -0,0 +1,15 @@
+package api
+
+import (
+	"github.com/ArionMiles/expensor/backend/internal/store"
+)
+
+var (
+	_ appConfigReader = (*store.Store)(nil)
+	_ appConfigWriter = (*store.Store)(nil)
+	_ statsReader     = (*store.Store)(nil)
+
+	_ appConfigReader = (*store.InstrumentedStore)(nil)
+	_ appConfigWriter = (*store.InstrumentedStore)(nil)
+	_ statsReader     = (*store.InstrumentedStore)(nil)
+)