// Package menu renders Crucible's interactive launcher: a numbered list of
// commands for users who don't want to memorize subcommands. It holds no
// builder logic — it returns the chosen dispatcher argument slice for the
// caller to run. This is the seed of a future GUI front-end over the same core.
package menu

import (
	"bufio"
	"fmt"
	"io"
	"strconv"
	"strings"
)

// Item is one selectable command.
type Item struct {
	Label   string   // e.g. "module build"
	Desc    string   // e.g. "build the configured module"
	Args    []string // dispatcher args, e.g. {"module", "build"}
	Usage   string
	Options []string
}

// ANSI styling; terminals that don't support it simply ignore the codes.
const (
	cReset = "\033[0m"
	cBold  = "\033[1m"
	cCyan  = "\033[36m"
	cDim   = "\033[2m"
)

// Select prints the numbered menu to out, reads a selection plus optional extra
// arguments from in, and returns the full dispatcher argument slice. It returns
// (nil, nil) when the user quits or enters an empty choice.
func Select(out io.Writer, in io.Reader, items []Item) ([]string, error) {
	if len(items) == 0 {
		return nil, fmt.Errorf("no commands available")
	}
	fmt.Fprintf(out, "%s%sCrucible%s — pick a command:\n\n", cBold, cCyan, cReset)
	labelWidth := 0
	for _, item := range items {
		if len(item.Label) > labelWidth {
			labelWidth = len(item.Label)
		}
	}
	for i, it := range items {
		fmt.Fprintf(out, "  %s%2d%s  %s%-*s%s  %s%s%s\n",
			cCyan, i+1, cReset, cBold, labelWidth, it.Label, cReset, cDim, it.Desc, cReset)
	}
	fmt.Fprintf(out, "   %sq%s  quit\n\nselection: ", cCyan, cReset)

	r := bufio.NewReader(in)
	line, _ := r.ReadString('\n')
	switch choice := strings.TrimSpace(line); choice {
	case "", "q", "Q":
		return nil, nil
	default:
		n, err := strconv.Atoi(choice)
		if err != nil || n < 1 || n > len(items) {
			return nil, fmt.Errorf("invalid selection %q", choice)
		}
		it := items[n-1]
		if it.Usage != "" {
			fmt.Fprintf(out, "\nusage: %s\n", it.Usage)
		}
		if len(it.Options) > 0 {
			fmt.Fprintln(out, "options:")
			for _, option := range it.Options {
				fmt.Fprintf(out, "  %s\n", option)
			}
		}
		fmt.Fprint(out, "\narguments (press Enter to use defaults): ")
		argLine, _ := r.ReadString('\n')
		extra := strings.Fields(strings.TrimSpace(argLine))
		return append(append([]string{}, it.Args...), extra...), nil
	}
}