sdk: add a logger interface

we are now ready to make the sdk a separate module

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

sdk/logger/logger.go

@@ -0,0 +1,56 @@
+// Package logger provides logging capabilities.
+package logger
+
+import "github.com/hashicorp/go-hclog"
+
+var (
+	logger Logger
+)
+
+func init() {
+	DisableLogger()
+}
+
+// Logger interface
+type Logger interface {
+	// LogWithKeyVals logs at the specified level for the specified sender adding the specified key vals
+	LogWithKeyVals(level hclog.Level, sender, msg string, args ...interface{})
+	// Log logs at the specified level for the specified sender
+	Log(level hclog.Level, sender, format string, v ...interface{})
+}
+
+// SetLogger sets the specified logger
+func SetLogger(l Logger) {
+	logger = l
+}
+
+// DisableLogger disables logging
+func DisableLogger() {
+	logger = &noLogger{}
+}
+
+type noLogger struct{}
+
+func (*noLogger) LogWithKeyVals(level hclog.Level, sender, msg string, args ...interface{}) {}
+
+func (*noLogger) Log(level hclog.Level, sender, format string, v ...interface{}) {}
+
+// Debug logs at debug level for the specified sender
+func Debug(sender, format string, v ...interface{}) {
+	logger.Log(hclog.Debug, sender, format, v...)
+}
+
+// Info logs at info level for the specified sender
+func Info(sender, format string, v ...interface{}) {
+	logger.Log(hclog.Info, sender, format, v...)
+}
+
+// Warn logs at warn level for the specified sender
+func Warn(sender, format string, v ...interface{}) {
+	logger.Log(hclog.Warn, sender, format, v...)
+}
+
+// Error logs at error level for the specified sender
+func Error(sender, format string, v ...interface{}) {
+	logger.Log(hclog.Error, sender, format, v...)
+}