Add a couple of overridable completion functions (#3)

There are more times that we can tap into providing support for.
For now, set up the following types with overridable completion handler
functions:
- Space, Org, AppName
- Binding Name (this more for further experimentation)

ai-assisted=no
TNZ-87450

Author: vuil

command/flag/arguments.go

@@ -1,5 +1,29 @@
 package flag
 
+import flags "github.com/jessevdk/go-flags"
+
+// List of overridable completion function for various types
+
+var SpaceCompleteFunc = func(prefix string) []flags.Completion { return nil }
+
+func (Space) Complete(prefix string) []flags.Completion {
+	return SpaceCompleteFunc(prefix)
+}
+
+var OrganizationCompleteFunc = func(prefix string) []flags.Completion { return nil }
+
+func (Organization) Complete(prefix string) []flags.Completion {
+	return OrganizationCompleteFunc(prefix)
+}
+
+var AppNameCompleteFunc = func(prefix string) []flags.Completion { return nil }
+
+func (AppName) Complete(prefix string) []flags.Completion {
+	return AppNameCompleteFunc(prefix)
+}
+
+// --------------------------------------------------------------------------------------------------
+
 type AppName struct {
 	AppName string `positional-arg-name:"APP_NAME" required:"true" description:"The application name"`
 }

command/flag/binding_name.go

@@ -6,6 +6,12 @@ type BindingName struct {
 	Value string
 }
 
+var BindingNameCompleteFunc = func(prefix string) []flags.Completion { return nil }
+
+func (BindingName) Complete(prefix string) []flags.Completion {
+	return BindingNameCompleteFunc(prefix)
+}
+
 func (b *BindingName) UnmarshalFlag(val string) error {
 	if val == "" {
 		return &flags.Error{

command/flag/binding_name_test.go

@@ -30,4 +30,47 @@ var _ = Describe("BindingName", func() {
 			Expect(bindingName.Value).To(Equal("some-name"))
 		})
 	})
+
+	Describe("Complete", func() {
+		When("BindingNameCompleteFunc is not set", func() {
+			It("returns nil", func() {
+				result := bindingName.Complete("test-")
+				Expect(result).To(BeNil())
+			})
+		})
+
+		When("BindingNameCompleteFunc is set", func() {
+			It("calls BindingNameCompleteFunc with the provided prefix and returns the result", func() {
+				expectedCompletions := []flags.Completion{
+					{Item: "binding-1"},
+					{Item: "binding-2"},
+				}
+				BindingNameCompleteFunc = func(prefix string) []flags.Completion {
+					return expectedCompletions
+				}
+				defer func() {
+					BindingNameCompleteFunc = func(prefix string) []flags.Completion { return nil }
+				}()
+
+				result := bindingName.Complete("binding-")
+				Expect(result).To(Equal(expectedCompletions))
+			})
+		})
+
+		When("Complete is called with different prefixes", func() {
+			It("passes the prefix correctly to BindingNameCompleteFunc", func() {
+				var capturedPrefix string
+				BindingNameCompleteFunc = func(prefix string) []flags.Completion {
+					capturedPrefix = prefix
+					return nil
+				}
+				defer func() {
+					BindingNameCompleteFunc = func(prefix string) []flags.Completion { return nil }
+				}()
+
+				bindingName.Complete("my-prefix")
+				Expect(capturedPrefix).To(Equal("my-prefix"))
+			})
+		})
+	})
 })