fix: move implementation to "internal" package

internal/log/default.go

@@ -0,0 +1,56 @@
+package log
+
+import (
+	"fmt"
+	"log"
+	"log/slog"
+	"strings"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	errorMetric = promauto.NewCounter(
+		prometheus.CounterOpts{
+			Name: "spendsparrow_error_total",
+			Help: "The total number of errors during processing",
+		},
+	)
+)
+
+func Fatal(message string, args ...interface{}) {
+	errorMetric.Inc()
+
+	s := format(message, args)
+	log.Fatal(s)
+}
+
+func Error(message string, args ...interface{}) {
+	errorMetric.Inc()
+
+	s := format(message, args)
+	slog.Error(s)
+}
+
+func Warn(message string, args ...interface{}) {
+	s := format(message, args)
+	slog.Warn(s)
+}
+
+func Info(message string, args ...interface{}) {
+	s := format(message, args)
+	slog.Info(s)
+}
+
+func format(message string, args []interface{}) string {
+	var w strings.Builder
+
+	if len(args) > 0 {
+		fmt.Fprintf(&w, message, args...)
+	} else {
+		w.WriteString(message)
+	}
+
+	return w.String()
+}