package command

import (
	"errors"
	"fmt"
	"io"
	"strings"
	"text/tabwriter"
)

var ErrHelp = errors.New("help requested")

type helpBuilder struct {
	n      *node
	prefix []string
}

func (h *helpBuilder) writeHelp(w io.Writer) error {
	if _, err := fmt.Fprintf(w,
		"\nUsage:\t%s%s COMMAND [OPTIONS]\n\nCommands:\n",
		strings.Join(h.prefix, " "), &h.n.su); err != nil {
		return err
	}

	tw := tabwriter.NewWriter(w, 0, 1, 4, ' ', 0)
	if err := h.writeCommands(h.n.child, tw); err != nil {
		return err
	}
	if err := tw.Flush(); err != nil {
		return err
	}

	_, err := w.Write([]byte{'\n'})
	if err == nil {
		err = ErrHelp
	}
	return err
}

func (h *helpBuilder) writeCommands(n *node, w io.Writer) error {
	if n == nil {
		return nil
	}
	if _, err := fmt.Fprintf(w, "\t%s\t%s\n", n.name, n.usage); err != nil {
		return err
	}
	return h.writeCommands(n.next, w)
}