refactor: Move code from main into sub packages

Move internal logic into `internal/fn` and expose constructor in
`pkg/fn` that can be importet in other modules.

Signed-off-by: Maximilian Blatt <maximilian.blatt-extern@deutschebahn.com>

fn.go → internal/fn/fn.go

@@ -1,4 +1,4 @@
-package main
+package fn
 
 import (
 	"bytes"
@@ -43,6 +43,35 @@ type Function struct {
 	fsys fs.FS
 }
 
+// FunctionOpt can modify a Function upon creation.
+type FunctionOpt func(f *Function)
+
+// WithLogger adds a logger to a Function.
+func WithLogger(log logging.Logger) FunctionOpt {
+	return func(f *Function) { f.log = log }
+}
+
+// WithFilesystem adds a filesystem to a Function.
+func WithFileSystem(fsys fs.FS) FunctionOpt {
+	return func(f *Function) { f.fsys = fsys }
+}
+
+// NewFunction creates a new Function with the given options.
+func NewFunction(opts ...FunctionOpt) *Function {
+	f := &Function{}
+	for _, opt := range opts {
+		opt(f)
+	}
+	// Set defaults
+	if f.fsys == nil {
+		f.fsys = &osFS{}
+	}
+	if f.log == nil {
+		f.log = logging.NewNopLogger()
+	}
+	return f
+}
+
 const (
 	annotationKeyCompositionResourceName = "gotemplating.fn.crossplane.io/composition-resource-name"
 	annotationKeyReady                   = "gotemplating.fn.crossplane.io/ready"

fn_test.go → internal/fn/fn_test.go

@@ -1,4 +1,4 @@
-package main
+package fn
 
 import (
 	"context"
@@ -11,8 +11,6 @@ import (
 	"google.golang.org/protobuf/testing/protocmp"
 	"google.golang.org/protobuf/types/known/durationpb"
 
-	"github.com/crossplane/crossplane-runtime/pkg/logging"
-
 	fnv1beta1 "github.com/crossplane/function-sdk-go/proto/v1beta1"
 	"github.com/crossplane/function-sdk-go/resource"
 	"github.com/crossplane/function-sdk-go/response"
@@ -591,10 +589,9 @@ func TestRunFunction(t *testing.T) {
 
 	for name, tc := range cases {
 		t.Run(name, func(t *testing.T) {
-			f := &Function{
-				log:  logging.NewNopLogger(),
-				fsys: testdataFS,
-			}
+			f := NewFunction(
+				WithFileSystem(testdataFS),
+			)
 			rsp, err := f.RunFunction(tc.args.ctx, tc.args.req)
 
 			if diff := cmp.Diff(tc.want.rsp, rsp, protocmp.Transform()); diff != "" {

function_maps.go → internal/fn/function_maps.go

@@ -1,4 +1,4 @@
-package main
+package fn
 
 import (
 	"fmt"
@@ -41,7 +41,7 @@ func GetNewTemplateWithFunctionMaps(delims *v1beta1.Delims) *template.Template {
 		tpl.Funcs(f)
 	}
 	tpl.Funcs(template.FuncMap{
-			"include": initInclude(tpl),
+		"include": initInclude(tpl),
 	})
 	tpl.Funcs(sprig.FuncMap())
 
@@ -103,4 +103,4 @@ func initInclude(t *template.Template) func(string, interface{}) (string, error)
 		return buf.String(), err
 	}
 
-}
+}

function_maps_test.go → internal/fn/function_maps_test.go

@@ -1,4 +1,4 @@
-package main
+package fn
 
 import (
 	"bytes"
@@ -32,7 +32,7 @@ func Test_fromYaml(t *testing.T) {
 complexDictionary:
   scalar1: true
   list:
-  - abc	
+  - abc
   - def`,
 			},
 			want: want{

template.go → internal/fn/template.go

@@ -1,4 +1,4 @@
-package main
+package fn
 
 import (
 	"io/fs"

main.go

@@ -5,6 +5,8 @@ import (
 	"github.com/alecthomas/kong"
 
 	"github.com/crossplane/function-sdk-go"
+
+	"github.com/crossplane-contrib/function-go-templating/pkg/fn"
 )
 
 // CLI of this Function.
@@ -24,11 +26,7 @@ func (c *CLI) Run() error {
 		return err
 	}
 
-	return function.Serve(
-		&Function{
-			log:  log,
-			fsys: &osFS{},
-		},
+	return function.Serve(fn.NewFunction(fn.WithLogger(log)),
 		function.Listen(c.Network, c.Address),
 		function.MTLSCertificates(c.TLSCertsDir),
 		function.Insecure(c.Insecure))

pkg/fn/fn.go

@@ -0,0 +1,17 @@
+// Package fn defines the public interface for patch-and-transform functions.
+package fn
+
+import (
+	fninternal "github.com/crossplane-contrib/function-go-templating/internal/fn"
+)
+
+var (
+	// NewFunction creates a new Function with the given options.
+	NewFunction = fninternal.NewFunction
+
+	// WithLogger adds a logger to a Function.
+	WithLogger = fninternal.WithLogger
+
+	// WithFilesystem adds a filesystem to a Function.
+	WithFileSystem = fninternal.WithFileSystem
+)