refactor: extract core logic to a plain Go package

commands/list.go

@@ -0,0 +1,72 @@
+package commands
+
+import (
+	"io"
+
+	"github.com/jimeh/evm/manager"
+	"github.com/spf13/cobra"
+)
+
+func NewList(mgr *manager.Manager) (*cobra.Command, error) {
+	cmd := &cobra.Command{
+		Use: "list",
+		Short: "List all Emacs versions found in " +
+			"`$EVM_ROOT/versions/*'",
+		Aliases:           []string{"ls", "versions"},
+		Args:              cobra.ExactArgs(0),
+		ValidArgsFunction: noValidArgs,
+		RunE:              listRunE(mgr),
+	}
+
+	cmd.Flags().StringP("format", "f", "", "output format (yaml or json)")
+
+	return cmd, nil
+}
+
+func listRunE(mgr *manager.Manager) runEFunc {
+	return func(cmd *cobra.Command, _ []string) error {
+		format := flagString(cmd, "format")
+
+		versions, err := mgr.List(cmd.Context())
+		if err != nil {
+			return err
+		}
+
+		output := &listOutput{
+			Current:  mgr.CurrentVersion(),
+			SetBy:    mgr.CurrentSetBy(),
+			Versions: versions,
+		}
+
+		return render(cmd.OutOrStdout(), format, output)
+	}
+}
+
+type listOutput struct {
+	Current  string             `yaml:"current" json:"current"`
+	SetBy    string             `yaml:"current_set_by,omitempty" json:"current_set_by,omitempty"`
+	Versions []*manager.Version `yaml:"versions" json:"versions"`
+}
+
+func (lr *listOutput) WriteTo(w io.Writer) (int64, error) {
+	var b []byte
+
+	for _, ver := range lr.Versions {
+		if lr.Current == ver.Version {
+			b = append(b, []byte("* ")...)
+		} else {
+			b = append(b, []byte("  ")...)
+		}
+
+		b = append(b, []byte(ver.Version)...)
+		if lr.Current == ver.Version && lr.SetBy != "" {
+			b = append(b, []byte(" (set by "+lr.SetBy+")")...)
+		}
+
+		b = append(b, byte('\n'))
+	}
+
+	n, err := w.Write(b)
+
+	return int64(n), err
+}