feat: add display decorator (#11)

* add display decorator

* rename decorator name

* add header

* update type

* add tests and uses cobra stdout and err

* add header

* update description

decorators.go

@@ -30,6 +30,8 @@ import (
 
 var DefaultDecorators = []Decorator{
 	CommandWithLoggerDecorator{},
+	CommandWithOutputDecorator{},
+
 	CommandWithAliasesDecorator{},
 	CommandWithFlagsDecorator{},
 
@@ -81,6 +83,36 @@ func (d CommandWithLoggerDecorator) Decorate(_ *Ecdysis, _ *cobra.Command, c Com
 	return nil
 }
 
+// -- OUTPUT -------------------------------------------------------------------
+
+// CommandWithOutput can be implemented by a command to provide its own stdout and stderr.
+type CommandWithOutput interface {
+	Command
+	Output(output Output)
+}
+
+// CommandWithOutputDecorator is a decorator that provides a Stdout to the command.
+// If the Stdout field is not set, the default stdout will be provided.
+type CommandWithOutputDecorator struct {
+	Output Output
+}
+
+// Decorate provides the logger to the command.
+func (d CommandWithOutputDecorator) Decorate(_ *Ecdysis, cmd *cobra.Command, c Command) error {
+	v, ok := c.(CommandWithOutput)
+	if !ok {
+		return nil
+	}
+
+	if d.Output == nil {
+		v.Output(NewDefaultOutput(cmd))
+	} else {
+		v.Output(d.Output)
+	}
+
+	return nil
+}
+
 // -- ALIASES ------------------------------------------------------------------
 
 // CommandWithAliases can be implemented by a command to provide aliases.

go.mod

@@ -4,6 +4,7 @@ go 1.23.0
 
 require (
 	github.com/google/go-cmp v0.6.0
+	github.com/matryer/is v1.4.1
 	github.com/spf13/cobra v1.8.1
 	github.com/spf13/pflag v1.0.5
 	github.com/spf13/viper v1.19.0

go.sum

@@ -19,6 +19,8 @@ github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/magiconair/properties v1.8.7 h1:IeQXZAiQcpL9mgcAe1Nu6cX9LLw6ExEHKjN0VQdvPDY=
 github.com/magiconair/properties v1.8.7/go.mod h1:Dhd985XPs7jluiymwWYZ0G4Z61jb3vdS329zhj2hYo0=
+github.com/matryer/is v1.4.1 h1:55ehd8zaGABKLXQUe2awZ99BD/PTc2ls+KV/dXphgEQ=
+github.com/matryer/is v1.4.1/go.mod h1:8I/i5uYgLzgsgEloJE1U6xx5HkBQpAZvepWuujKwMRU=
 github.com/mitchellh/mapstructure v1.5.0 h1:jeMsZIYE/09sWLaz43PL7Gy6RuMjD2eJVyuac5Z2hdY=
 github.com/mitchellh/mapstructure v1.5.0/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
 github.com/pelletier/go-toml/v2 v2.2.2 h1:aYUidT7k73Pcl9nb2gScu7NSrKCSHIDE89b3+6Wq+LM=

output.go

@@ -0,0 +1,59 @@
+// Copyright © 2025 Meroxa, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ecdysis
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/spf13/cobra"
+)
+
+type Output interface {
+	Stdout(any)
+	Stderr(any)
+}
+
+type DefaultOutput struct {
+	stdout io.Writer
+	stderr io.Writer
+}
+
+func NewDefaultOutput(cmd *cobra.Command) *DefaultOutput {
+	return &DefaultOutput{
+		stdout: cmd.OutOrStdout(),
+		stderr: cmd.OutOrStderr(),
+	}
+}
+
+// Stdout writes a message to the configured standard output.
+func (d *DefaultOutput) Stdout(msg any) {
+	fmt.Fprint(d.stdout, msg)
+}
+
+// Stderr writes a message to the configured standard error.
+func (d *DefaultOutput) Stderr(msg any) {
+	fmt.Fprint(d.stderr, msg)
+}
+
+// Output allows overwriting the stdout and/or stderr for specific use cases (like testing).
+func (d *DefaultOutput) Output(stdout, stderr io.Writer) {
+	if stdout != nil {
+		d.stdout = stdout
+	}
+	if stderr != nil {
+		d.stderr = stderr
+	}
+}

output_test.go

@@ -0,0 +1,73 @@
+// Copyright © 2025 Meroxa, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package ecdysis
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/matryer/is"
+	"github.com/spf13/cobra"
+)
+
+func TestNewDefaultOutput(t *testing.T) {
+	is := is.New(t)
+	cmd := &cobra.Command{}
+	out := NewDefaultOutput(cmd)
+
+	is.Equal(out.stdout, cmd.OutOrStdout())
+	is.Equal(out.stderr, cmd.OutOrStderr())
+}
+
+func TestStdout(t *testing.T) {
+	is := is.New(t)
+
+	var buf bytes.Buffer
+	out := &DefaultOutput{stdout: &buf}
+
+	message := "hello stdout"
+	out.Stdout(message)
+
+	is.Equal(buf.String(), message)
+}
+
+func TestStderr(t *testing.T) {
+	is := is.New(t)
+
+	var buf bytes.Buffer
+	out := &DefaultOutput{stderr: &buf}
+
+	message := "hello stderr"
+	out.Stderr(message)
+
+	is.Equal(buf.String(), message)
+}
+
+func TestOutput(t *testing.T) {
+	is := is.New(t)
+
+	var stdoutBuf, stderrBuf bytes.Buffer
+	out := &DefaultOutput{}
+
+	out.Output(&stdoutBuf, &stderrBuf)
+
+	stdoutMsg := "stdout test"
+	stderrMsg := "stderr test"
+	out.Stdout(stdoutMsg)
+	out.Stderr(stderrMsg)
+
+	is.Equal(stdoutMsg, stdoutBuf.String())
+	is.Equal(stderrMsg, stderrBuf.String())
+}