package main

import (
	"fmt"
	"os"
	"strconv"
	"strings"
)

type Options struct {
	Verbose bool
	Count   int
	Name    string
	Args    []string
}

// ParseArgs parses flags and collects positional arguments.
func ParseArgs(args []string) (Options, error) {
	opts := Options{Count: 1}

	for i := 0; i < len(args); i++ {
		arg := args[i]

		if arg == "--" {
			opts.Args = append(opts.Args, args[i+1:]...)
			break
		}

		switch {
		case arg == "-v" || arg == "--verbose":
			opts.Verbose = true
		case arg == "-n" || arg == "--name":
			if i+1 >= len(args) {
				return opts, fmt.Errorf("%s requires a value", arg)
			}
			i++
			opts.Name = args[i]
		case strings.HasPrefix(arg, "--name="):
			opts.Name = strings.TrimPrefix(arg, "--name=")
		case arg == "-c" || arg == "--count":
			if i+1 >= len(args) {
				return opts, fmt.Errorf("%s requires a value", arg)
			}
			i++
			count, err := strconv.Atoi(args[i])
			if err != nil || count < 1 {
				return opts, fmt.Errorf("invalid count %q", args[i])
			}
			opts.Count = count
		case strings.HasPrefix(arg, "--count="):
			value := strings.TrimPrefix(arg, "--count=")
			count, err := strconv.Atoi(value)
			if err != nil || count < 1 {
				return opts, fmt.Errorf("invalid count %q", value)
			}
			opts.Count = count
		case strings.HasPrefix(arg, "-"):
			return opts, fmt.Errorf("unknown option %q", arg)
		default:
			opts.Args = append(opts.Args, arg)
		}
	}

	return opts, nil
}

// runTests provides a couple of lightweight parser checks.
func runTests() error {
	tests := []struct {
		args []string
		want Options
	}{
		{
			args: []string{"--verbose", "--name=Ada", "--count", "2", "file.txt"},
			want: Options{Verbose: true, Name: "Ada", Count: 2, Args: []string{"file.txt"}},
		},
		{
			args: []string{"--", "--verbose"},
			want: Options{Count: 1, Args: []string{"--verbose"}},
		},
	}

	for i, test := range tests {
		got, err := ParseArgs(test.args)
		if err != nil {
			return fmt.Errorf("test %d: unexpected error: %w", i+1, err)
		}
		if fmt.Sprintf("%#v", got) != fmt.Sprintf("%#v", test.want) {
			return fmt.Errorf("test %d: got %#v, want %#v", i+1, got, test.want)
		}
	}
	return nil
}

func main() {
	if len(os.Args) == 2 && os.Args[1] == "--self-test" {
		if err := runTests(); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		fmt.Println("tests passed")
		return
	}

	opts, err := ParseArgs(os.Args[1:])
	if err != nil {
		fmt.Fprintln(os.Stderr, "error:", err)
		os.Exit(2)
	}

	fmt.Printf("verbose=%t name=%q count=%d args=%v\n",
		opts.Verbose, opts.Name, opts.Count, opts.Args)
}