Add debug mode and logging

_example/go.mod

@@ -2,6 +2,6 @@ module github.com/ivanglie/go-coingate-client/_example
 
 go 1.16
 
-require github.com/ivanglie/go-coingate-client v1.0.0
+require github.com/ivanglie/go-coingate-client v1.0.1
 
 replace github.com/ivanglie/go-coingate-client => ../

coingate.go

@@ -4,12 +4,15 @@ import (
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
-	"log"
 	"strconv"
 )
 
 const baseURL = "https://api.coingate.com/v2/rates/merchant"
 
+// Debug mode
+// If this variable is set to true, debug mode activated for the package
+var Debug = false
+
 // CoinGate API error responses
 // Response example:
 // {
@@ -27,7 +30,9 @@ type Error struct {
 // Arguments are ISO Symbol. Example: EUR, USD, BTC, ETH, etc.
 // See https://developer.coingate.com/docs/get-rate
 func getRate(from, to string, fetch FetchFunction) (float64, error) {
-	log.Printf("Fetching the currency rate for %s\n", to)
+	if Debug {
+		log.Printf("Fetching the currency rate for %s\n", to)
+	}
 
 	var res float64 = 0
 	url := fmt.Sprintf("%s/%s/%s", baseURL, from, to)

log.go

@@ -0,0 +1,24 @@
+package coingate
+
+import (
+	"errors"
+	stdlog "log"
+	"os"
+)
+
+// Logger is an interface that represents the required methods to log data.
+type Logger interface {
+	Println(v ...interface{})
+	Printf(format string, v ...interface{})
+}
+
+var log Logger = stdlog.New(os.Stderr, "", stdlog.LstdFlags)
+
+// SetLogger specifies the logger that the package should use.
+func SetLogger(logger Logger) error {
+	if logger == nil {
+		return errors.New("logger is nil")
+	}
+	log = logger
+	return nil
+}