mama-dns-tool/cmd/output.go

package cmd

import (
	"encoding/json"
	"fmt"
	"io"
	"strings"
	"text/tabwriter"
)

// outputFormat is a rendering mode for command results.
type outputFormat string

const (
	formatTable outputFormat = "table"
	formatJSON  outputFormat = "json"
)

// parseFormat validates a user-supplied format name.
func parseFormat(s string) (outputFormat, error) {
	switch outputFormat(strings.ToLower(strings.TrimSpace(s))) {
	case formatTable, "":
		return formatTable, nil
	case formatJSON:
		return formatJSON, nil
	default:
		return "", fmt.Errorf("unknown output format %q: use table or json", s)
	}
}

// writeOutput renders v according to format. Table rendering uses header and
// rows so every command lays out the same way.
func writeOutput(w io.Writer, format outputFormat, header []string, rows [][]string, v any) error {
	if format == formatJSON {
		enc := json.NewEncoder(w)
		enc.SetIndent("", "  ")
		return enc.Encode(v)
	}
	if len(header) == 0 && len(rows) == 0 {
		return nil
	}
	tw := tabwriter.NewWriter(w, 0, 0, 2, ' ', 0)
	if len(header) > 0 {
		fmt.Fprintln(tw, strings.Join(header, "\t"))
	}
	for _, row := range rows {
		fmt.Fprintln(tw, strings.Join(row, "\t"))
	}
	return tw.Flush()
}