[#1041] cmd/*: factor out autocomplet command generation

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/util/autocomplete/autocomplete.go

@@ -0,0 +1,65 @@
+package autocomplete
+
+import (
+	"fmt"
+	"os"
+
+	"github.com/spf13/cobra"
+)
+
+const longHelpTemplate = `To load completions:
+
+Bash:
+
+$ source <(%s completion bash)
+
+# To load completions for each session, execute once:
+Linux:
+  $ %s completion bash > /etc/bash_completion.d/%s
+MacOS:
+  $ %s completion bash > /usr/local/etc/bash_completion.d/%s
+
+Zsh:
+
+# If shell completion is not already enabled in your environment you will need
+# to enable it.  You can execute the following once:
+
+$ echo "autoload -U compinit; compinit" >> ~/.zshrc
+
+# To load completions for each session, execute once:
+$ %s completion zsh > "${fpath[1]}/_%s"
+
+# You will need to start a new shell for this setup to take effect.
+
+Fish:
+
+$ %s completion fish | source
+
+# To load completions for each session, execute once:
+$ %s completion fish > ~/.config/fish/completions/%s.fish
+`
+
+// Command returns cobra command structure for autocomplete routine.
+func Command(name string) *cobra.Command {
+	return &cobra.Command{
+		Use:   "completion [bash|zsh|fish|powershell]",
+		Short: "Generate completion script",
+		Long: fmt.Sprintf(longHelpTemplate,
+			name, name, name, name, name, name, name, name, name, name),
+		DisableFlagsInUseLine: true,
+		ValidArgs:             []string{"bash", "zsh", "fish", "powershell"},
+		Args:                  cobra.ExactValidArgs(1),
+		Run: func(cmd *cobra.Command, args []string) {
+			switch args[0] {
+			case "bash":
+				_ = cmd.Root().GenBashCompletion(os.Stdout)
+			case "zsh":
+				_ = cmd.Root().GenZshCompletion(os.Stdout)
+			case "fish":
+				_ = cmd.Root().GenFishCompletion(os.Stdout, true)
+			case "powershell":
+				_ = cmd.Root().GenPowerShellCompletion(os.Stdout)
+			}
+		},
+	}
+}