package main

import (
	"errors"
	"fmt"
	"strings"
)

var errUDPEmptyCommand = errors.New("interactive command is empty")

type udpInteractiveCommand struct {
	name  string
	to    string
	value string
}

func parseUDPInteractiveCommand(line string) (udpInteractiveCommand, error) {
	commandName, rest, ok := cutUDPField(strings.TrimSpace(line))
	if !ok {
		return udpInteractiveCommand{}, errUDPEmptyCommand
	}

	switch strings.ToLower(commandName) {
	case "help", "h", "?":
		return udpInteractiveCommand{name: "help"}, nil
	case "quit", "exit":
		return udpInteractiveCommand{name: "quit"}, nil
	case "text":
		to, body, err := parseUDPTargetValue(rest, "text")
		if err != nil {
			return udpInteractiveCommand{}, err
		}
		return udpInteractiveCommand{name: "text", to: to, value: body}, nil
	case "file":
		to, path, err := parseUDPTargetValue(rest, "file")
		if err != nil {
			return udpInteractiveCommand{}, err
		}
		return udpInteractiveCommand{name: "file", to: to, value: path}, nil
	default:
		return udpInteractiveCommand{}, fmt.Errorf("unknown command %q; type help for usage", commandName)
	}
}

func parseUDPTargetValue(rest, commandName string) (string, string, error) {
	to, value, ok := cutUDPField(strings.TrimSpace(rest))
	if !ok {
		return "", "", fmt.Errorf("%s command requires a target peer and payload", commandName)
	}
	if strings.TrimSpace(value) == "" {
		return "", "", fmt.Errorf("%s command requires a non-empty payload", commandName)
	}

	return to, strings.TrimSpace(value), nil
}

func cutUDPField(input string) (string, string, bool) {
	trimmed := strings.TrimSpace(input)
	if trimmed == "" {
		return "", "", false
	}

	for i, r := range trimmed {
		if r == ' ' || r == '\t' {
			return trimmed[:i], strings.TrimSpace(trimmed[i+1:]), true
		}
	}

	return trimmed, "", true
}