package main

import (
	"flag"
	"fmt"
	"os"
	"path/filepath"
	"strings"
)

var fileName = filepath.Base(os.Args[0])

func init() {
	fmt.Println("DNSHelper v1.0")
	fmt.Println("Copyright (c) 2024 Emberkom LLC")
	fmt.Println("")
	if len(os.Args) < 2 {
		printUsage()
		defer os.Exit(1)
	}
}

func printUsage() {
	fmt.Println("This utility will update the local hosts file with DNS entries obtained by the specified DNS server.")
	fmt.Println("Usage: " + fileName + " [add|delete] -host hostname [-server dns.example.com]")
	fmt.Println("Example:")
	fmt.Println("       " + fileName + " add -host xyz.acme.com -server dns.example.com")
	fmt.Println("         This will use dns.example.com to find and add all IP addresses for xyz.acme.com to the local hosts file.")
	fmt.Println("       " + fileName + " delete -host hostname.example.com")
	fmt.Println("         This will delete all entries for hostname.example.com from the local hosts file.")
	fmt.Println("       " + fileName + " delete all")
	fmt.Println("         This will delete all entries from the local hosts file that were added by this utility.")
	fmt.Println("Note: Adding a hostname will first remove all entries in the hosts file that match the same hostname.")
	fmt.Println("      This utility will only remove entries from the hosts file that it added.")
}

func term(err error) {
	fmt.Println("Error: " + err.Error())
	defer os.Exit(1)
}

func main() {
	modePing := flag.NewFlagSet("ping", flag.ExitOnError)
	modeAdd := flag.NewFlagSet("add", flag.ExitOnError)
	hostToAdd := modeAdd.String("host", "", "Comma separated list of hostnames to add")
	dnsResolver := modeAdd.String("server", "", "DNS resolver to use")
	modeDelete := flag.NewFlagSet("delete", flag.ExitOnError)
	hostToDelete := modeDelete.String("host", "", "Comma separated list of hostnames to delete")

	data := new(workingData)

	var err error
	data.HostsFileLocation, err = getHostsFileLocation()
	if err != nil {
		term(err)
	}

	data.DefaultContent, err = getFileContentLines(data.HostsFileLocation)
	if err != nil {
		term(err)
	}

	if err = extractLinesToEdit(data); err != nil {
		term(err)
	}

	switch strings.ToLower(os.Args[1]) {
	case "a", "add":
		err = modeAdd.Parse(os.Args[2:])
		if err != nil {
			term(err)
		}
		addHostsToWorkingData(data, hostToAdd)
		addResolversToWorkingData(data, dnsResolver)
		removeHostsFromExistingContent(data)
		addNameToIPMappingsToNewContent(data)
	case "d", "del", "delete":
		err = modeDelete.Parse(os.Args[2:])
		if err != nil {
			term(err)
		}
		if strings.ToLower(*hostToDelete) != "all" && strings.ToLower(*hostToDelete) != "a" {
			addHostsToWorkingData(data, hostToDelete)
			removeHostsFromExistingContent(data)
		}
	default:
		printUsage()
	}

	err = writeHostsFile(data)
	if err != nil {
		term(err)
	}
}