imagefilter: add ResultFormatter type to support flexible output

This commit adds a new `ResultFormatter` interface that supports
outputing the results as text or JSON.

Note that the text output should be copy/paste friendly, i.e. the
"image-builder" cmdline (or other consuemrs) should support:
```
$ image-builder manifest centos-9 type:qcow2 arch:s390
$ image-builder build centos-9 type:qcow2 arch:x86_64
```
(and of course `build` will need to error there is an architecture
 mistach like host-arch != target-arch).

pkg/imagefilter/formatter.go

@@ -0,0 +1,96 @@
+package imagefilter
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+)
+
+// OutputFormat contains the valid output formats for formatting results
+type OutputFormat string
+
+const (
+	OutputFormatDefault OutputFormat = ""
+	OutputFormatText    OutputFormat = "text"
+	OutputFormatJSON    OutputFormat = "json"
+)
+
+// ResultFormatter will format the given result list to the given io.Writer
+type ResultsFormatter interface {
+	Output(io.Writer, []Result) error
+}
+
+// NewResultFormatter will create a formatter based on the given format.
+func NewResultsFormatter(format OutputFormat) (ResultsFormatter, error) {
+	switch format {
+	case OutputFormatDefault, OutputFormatText:
+		return &textResultsFormatter{}, nil
+	case OutputFormatJSON:
+		return &jsonResultsFormatter{}, nil
+	default:
+		return nil, fmt.Errorf("unsupported formatter %q", format)
+	}
+}
+
+type textResultsFormatter struct{}
+
+func (*textResultsFormatter) Output(w io.Writer, all []Result) error {
+	var errs []error
+
+	for _, res := range all {
+		// The should be copy/paste friendly, i.e. the "image-builder"
+		// cmdline should support:
+		//   image-builder manifest centos-9 type:qcow2 arch:s390
+		//   image-builder build centos-9 type:qcow2 arch:x86_64
+		if _, err := fmt.Fprintf(w, "%s type:%s arch:%s\n", res.Distro.Name(), res.ImgType.Name(), res.Arch.Name()); err != nil {
+			errs = append(errs, err)
+		}
+	}
+	if len(errs) > 0 {
+		return errors.Join(errs...)
+	}
+
+	return nil
+}
+
+type jsonResultsFormatter struct{}
+
+type distroResultJSON struct {
+	Name string `json:"name"`
+}
+
+type archResultJSON struct {
+	Name string `json:"name"`
+}
+
+type imgTypeResultJSON struct {
+	Name string `json:"name"`
+}
+
+type filteredResultJSON struct {
+	Distro  distroResultJSON  `json:"distro"`
+	Arch    archResultJSON    `json:"arch"`
+	ImgType imgTypeResultJSON `json:"image_type"`
+}
+
+func (*jsonResultsFormatter) Output(w io.Writer, all []Result) error {
+	var out []filteredResultJSON
+
+	for _, res := range all {
+		out = append(out, filteredResultJSON{
+			Distro: distroResultJSON{
+				Name: res.Distro.Name(),
+			},
+			Arch: archResultJSON{
+				Name: res.Arch.Name(),
+			},
+			ImgType: imgTypeResultJSON{
+				Name: res.ImgType.Name(),
+			},
+		})
+	}
+
+	enc := json.NewEncoder(w)
+	return enc.Encode(out)
+}

pkg/imagefilter/formatter_test.go

@@ -0,0 +1,81 @@
+package imagefilter_test
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/osbuild/images/pkg/distrofactory"
+	"github.com/osbuild/images/pkg/imagefilter"
+)
+
+func newFakeResult(t *testing.T, resultSpec string) imagefilter.Result {
+	fac := distrofactory.NewTestDefault()
+
+	l := strings.Split(resultSpec, ":")
+	require.Equal(t, len(l), 3)
+
+	// XXX: it would be nice if TestDistro would support constructing
+	// like GetDistro("rhel-8.1:i386,amd64:ami,qcow2") that then
+	// creates test distro/type/arch on the fly instead of the current
+	// very static setup
+	di := fac.GetDistro(l[0])
+	require.NotNil(t, di)
+	ar, err := di.GetArch(l[2])
+	require.NoError(t, err)
+	im, err := ar.GetImageType(l[1])
+	require.NoError(t, err)
+	return imagefilter.Result{di, ar, im}
+}
+
+func TestResultsFormatter(t *testing.T) {
+
+	for _, tc := range []struct {
+		formatter     string
+		fakeResults   []string
+		expectsOutput string
+	}{
+		{
+			"",
+			[]string{"test-distro-1:qcow2:test_arch3"},
+			"test-distro-1 type:qcow2 arch:test_arch3\n",
+		},
+		{
+			"text",
+			[]string{"test-distro-1:qcow2:test_arch3"},
+			"test-distro-1 type:qcow2 arch:test_arch3\n",
+		},
+		{
+			"text",
+			[]string{
+				"test-distro-1:qcow2:test_arch3",
+				"test-distro-1:test_type:test_arch",
+			},
+			"test-distro-1 type:qcow2 arch:test_arch3\n" +
+				"test-distro-1 type:test_type arch:test_arch\n",
+		},
+		{
+			"json",
+			[]string{
+				"test-distro-1:qcow2:test_arch3",
+				"test-distro-1:test_type:test_arch",
+			},
+			`[{"distro":{"name":"test-distro-1"},"arch":{"name":"test_arch3"},"image_type":{"name":"qcow2"}},{"distro":{"name":"test-distro-1"},"arch":{"name":"test_arch"},"image_type":{"name":"test_type"}}]` + "\n",
+		},
+	} {
+		res := make([]imagefilter.Result, len(tc.fakeResults))
+		for i, resultSpec := range tc.fakeResults {
+			res[i] = newFakeResult(t, resultSpec)
+		}
+
+		var buf bytes.Buffer
+		fmter, err := imagefilter.NewResultsFormatter(imagefilter.OutputFormat(tc.formatter))
+		require.NoError(t, err)
+		err = fmter.Output(&buf, res)
+		assert.NoError(t, err)
+		assert.Equal(t, tc.expectsOutput, buf.String(), tc)
+	}
+}