entry: Add a new API for log related things

This needs improvement to eventually let the embedded application
disable logs from the main execution, or at least filter them through
itself to decide what to keep. That's a future complex project though.

entry/entry.go

@@ -76,9 +76,11 @@ type Data struct {
 	// Version is the version of this program, usually set at compile time.
 	Version string
 
-	// TODO: flags struct API here?
+	// Debug represents if we're running in debug mode or not.
 	Debug bool
-	//Verbose bool
+
+	// Logf is a logger which should be used.
+	Logf func(format string, v ...interface{})
 
 	// Args is the CLI struct to use. This takes the format of the go-arg
 	// API. Keep in mind that these values will be added on to the normal
@@ -260,7 +262,25 @@ func (obj *Runner) CLI(ctx context.Context, data *cliUtil.Data) error {
 	}
 	_ = args
 
+	//debug := data.Flags.Debug // this one comes from main
+	debug := obj.data.Debug // this one comes from entry
+	logf := func(format string, v ...interface{}) {
+		//data.Flags.Logf(obj.data.Program+": "+format, v...)
+		obj.data.Logf(obj.data.Program+": "+format, v...)
+	}
 	if obj.data.Custom != nil {
+		if x, ok := obj.data.Custom.(Initable); ok {
+			init := &Init{
+				Data:  data,
+				Debug: debug,
+				Logf:  logf,
+				// TODO: add more?
+			}
+			if err := x.Init(init); err != nil {
+				return errwrap.Wrapf(err, "can't init custom struct")
+			}
+		}
+
 		// The obj.data.Args value is our own Args struct which we can
 		// already have access to by holding on to it ourselves when we
 		// create it! So no need to pass it back in to ourselves...
@@ -296,6 +316,24 @@ func (obj *Runner) CLI(ctx context.Context, data *cliUtil.Data) error {
 	return nil
 }
 
+// Init is some data and handles to pass in.
+type Init struct {
+	// Data is the original data that we get from the core compilation.
+	Data *cliUtil.Data
+
+	Debug bool
+	Logf  func(format string, v ...interface{})
+}
+
+// Initable lets us have a way to pass in some data and handles if the struct
+// wants them. Implementing this is optional.
+type Initable interface {
+	Customizable
+
+	// Init passes in some data and handles.
+	Init(*Init) error
+}
+
 // Customizable is an additional API you can implement to have tighter control
 // over how the entry executes mgmt.
 // TODO: add an API with: func(arg.Config) (*arg.Parser, error) ?