Add machine-readable output formats

- Default table output (when stdout is attached to a terminal) stays the same;
- When stdout is redirected, output tab-separated values and no header line;
- With `--json` flag, output structured JSON data.

Example:

    $ ghcs list --json
    [
      {
        "Branch": "main",
        "Created At": "2021-06-10T15:04:46+02:00",
        "Name": "mislav-playground-jvqj",
        "Repository": "mislav/playground",
        "State": "Shutdown"
      },
      {
        "Branch": "master",
        "Created At": "2021-07-15T15:51:08+02:00",
        "Name": "mislav-github-github-pwgg365xv",
        "Repository": "github/github",
        "State": "Shutdown"
      }
    ]

cmd/ghcs/delete.go

@@ -73,7 +73,7 @@ func Delete(codespaceName string) error {
 
 	fmt.Println("Codespace deleted.")
 
-	return List()
+	return List(&ListOptions{})
 }
 
 func DeleteAll() error {
@@ -103,7 +103,7 @@ func DeleteAll() error {
 		fmt.Printf("Codespace deleted: %s\n", c.Name)
 	}
 
-	return List()
+	return List(&ListOptions{})
 }
 
 func DeleteByRepo(repo string) error {
@@ -143,5 +143,5 @@ func DeleteByRepo(repo string) error {
 		fmt.Printf("No codespace was found for repository: %s\n", repo)
 	}
 
-	return List()
+	return List(&ListOptions{})
 }

cmd/ghcs/list.go

@@ -5,21 +5,28 @@ import (
 	"fmt"
 	"os"
 
-	"github.com/olekukonko/tablewriter"
-
 	"github.com/github/ghcs/api"
+	"github.com/github/ghcs/cmd/ghcs/output"
 	"github.com/spf13/cobra"
 )
 
+type ListOptions struct {
+	AsJSON bool
+}
+
 func NewListCmd() *cobra.Command {
+	opts := &ListOptions{}
+
 	listCmd := &cobra.Command{
 		Use:   "list",
 		Short: "List GitHub Codespaces you have on your account.",
 		RunE: func(cmd *cobra.Command, args []string) error {
-			return List()
+			return List(opts)
 		},
 	}
 
+	listCmd.Flags().BoolVar(&opts.AsJSON, "json", false, "Output as JSON")
+
 	return listCmd
 }
 
@@ -27,7 +34,7 @@ func init() {
 	rootCmd.AddCommand(NewListCmd())
 }
 
-func List() error {
+func List(opts *ListOptions) error {
 	apiClient := api.New(os.Getenv("GITHUB_TOKEN"))
 	ctx := context.Background()
 
@@ -46,7 +53,7 @@ func List() error {
 		return nil
 	}
 
-	table := tablewriter.NewWriter(os.Stdout)
+	table := output.NewTable(os.Stdout, opts.AsJSON)
 	table.SetHeader([]string{"Name", "Repository", "Branch", "State", "Created At"})
 	for _, codespace := range codespaces {
 		table.Append([]string{

cmd/ghcs/output/format_json.go

@@ -0,0 +1,33 @@
+package output
+
+import (
+	"encoding/json"
+	"io"
+)
+
+type jsonwriter struct {
+	w      io.Writer
+	pretty bool
+	cols   []string
+	data   []interface{}
+}
+
+func (j *jsonwriter) SetHeader(cols []string) {
+	j.cols = cols
+}
+
+func (j *jsonwriter) Append(values []string) {
+	row := make(map[string]string)
+	for i, v := range values {
+		row[j.cols[i]] = v
+	}
+	j.data = append(j.data, row)
+}
+
+func (j *jsonwriter) Render() {
+	enc := json.NewEncoder(j.w)
+	if j.pretty {
+		enc.SetIndent("", "  ")
+	}
+	_ = enc.Encode(j.data)
+}

cmd/ghcs/output/format_table.go

@@ -0,0 +1,28 @@
+package output
+
+import (
+	"io"
+	"os"
+
+	"github.com/olekukonko/tablewriter"
+	"golang.org/x/term"
+)
+
+type Table interface {
+	SetHeader([]string)
+	Append([]string)
+	Render()
+}
+
+func NewTable(w io.Writer, asJSON bool) Table {
+	f, ok := w.(*os.File)
+	isTTY := ok && term.IsTerminal(int(f.Fd()))
+
+	if asJSON {
+		return &jsonwriter{w: w, pretty: isTTY}
+	}
+	if isTTY {
+		return tablewriter.NewWriter(w)
+	}
+	return &tabwriter{w: w}
+}

cmd/ghcs/output/format_tsv.go

@@ -0,0 +1,25 @@
+package output
+
+import (
+	"fmt"
+	"io"
+)
+
+type tabwriter struct {
+	w io.Writer
+}
+
+func (j *tabwriter) SetHeader([]string) {}
+
+func (j *tabwriter) Append(values []string) {
+	var sep string
+	for i, v := range values {
+		if i == 1 {
+			sep = "\t"
+		}
+		fmt.Fprintf(j.w, "%s%s", sep, v)
+	}
+	fmt.Fprint(j.w, "\n")
+}
+
+func (j *tabwriter) Render() {}