1 files changed, 63 insertions, 0 deletions
diff --git a/pkg/backend/callbacks.go b/pkg/backend/callbacks.go
new file mode 100644
index 0000000..5ea3b04
--- /dev/null
+++ b/pkg/backend/callbacks.go
@@ -0,0 +1,63 @@
+package backend
+
+import (
+	"fmt"
+	"reflect"
+	"sync"
+	"unsafe"
+)
+
+/* NOTE! ATCHUNG! what follow are not silly comments. Well, *this one* is, but
+   the lines after this are not.
+   Those are inline C functions, that are invoked by CGO later on.
+   it's also crucial that you don't any extra space between the function
+   block and the 'import "C"' line. */
+
+// typedef void (*cb)();
+// inline void _do_callback(cb f) {
+// 	f();
+// }
+import "C"
+
+/* callbacks into C-land */
+
+var mut sync.Mutex
+var stmut sync.Mutex
+var cbs = make(map[string](*[0]byte))
+var initOnce sync.Once
+
+// Events are just a enumeration of all the posible events that C functions can
+// be interested in subscribing to. You cannot subscribe to an event that is
+// not listed here.
+type Events struct {
+	OnStatusChanged string
+}
+
+const OnStatusChanged string = "OnStatusChanged"
+
+// subscribe registers a callback from C-land.
+// This callback needs to be passed as a void* C function pointer.
+func subscribe(event string, fp unsafe.Pointer) {
+	mut.Lock()
+	defer mut.Unlock()
+	e := &Events{}
+	v := reflect.Indirect(reflect.ValueOf(&e))
+	hf := v.Elem().FieldByName(event)
+	if reflect.ValueOf(hf).IsZero() {
+		fmt.Println("ERROR: not a valid event:", event)
+	} else {
+		cbs[event] = (*[0]byte)(fp)
+	}
+}
+
+// trigger fires a callback from C-land.
+func trigger(event string) {
+	mut.Lock()
+	defer mut.Unlock()
+	cb := cbs[event]
+	if cb != nil {
+		C._do_callback(cb)
+	} else {
+		fmt.Println("ERROR: this event does not have subscribers:", event)
+	}
+}