package main

import (
	"bufio"
	"errors"
	"fmt"
	"io"
	"log"
	"os"
	"os/signal"
	"os/user"
	"runtime"
	"time"

	"github.com/akamensky/argparse"
)

var (
	distractorsFile       string = "/etc/hyperfocus_distractors"
	predefDistractorsFile string = "/etc/hyperfocus_distractors_predefined"
	hostBackupFile        string = "/etc/.backup_hosts"
)

const resetDNSMsg string = `
Note that you may need to flush your system's DNS cache for changes to take effect.
In most cases this could be done by restarting the resolver daemon.
Windows systems: open PowerShell as administrator and run "ipconfig /flushdns"
macOS: open terminal and run "sudo dscacheutil -flushcache"
Linux with Systemd: open terminal and run "sudo systemctl restart systemd-resolved"
Other init systems or *BSD: You probably already know how to do this.`

// Check if <path> exists on the host filesystem
func fileExists(path string) bool {

	_, err := os.Stat(path)
	return !errors.Is(err, os.ErrNotExist)
}

// Copy src to dest
func copyFile(src string, dest string) error {

	origFile, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("could not open original file %s for copying: %s", src, err)
	}

	backupFile, err := os.OpenFile(dest, os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		return fmt.Errorf("could not open backup file %s for writing: %s", dest, err)
	}

	_, err = io.Copy(backupFile, origFile)
	if err != nil {
		return fmt.Errorf("could not copy %s to %s: %s", src, dest, err)
	}

	return nil
}

// Return system's host file as string
func getHostFile() string {

	var hostFile string
	switch runtime.GOOS {
	case "windows":
		hostFile = "/Windows/System32/drivers/etc/hosts"

	default:
		hostFile = "/etc/hosts"
	}

	return hostFile
}

// Check if running as super user
func isRoot() bool {

	currUser, err := user.Current()
	if err != nil {
		log.Fatalf("[Super user check] Unable to get current user: %s\n", err)
	}

	return currUser.Username == "root"
}

// Disables access to websites that are defined as 'distractors'
func improveFocus() {

	// Backup host file if a backup does not already exist
	if !fileExists(hostBackupFile) {
		if err := copyFile(getHostFile(), hostBackupFile); err != nil {
			log.Fatalln(err)
		}
	}

	// Open host file for writing/appending
	hostFile, err := os.OpenFile(getHostFile(), os.O_APPEND|os.O_WRONLY, 0666)
	if err != nil {
		log.Fatalln(err)
	}
	defer hostFile.Close()

	// For checking if /etc/hyperfocus_distractors or /etc/hyperfocus_distractors_predefined
	// exist.
	var (
		distractorsFileWarn       bool
		predefDistractorsFileWarn bool
	)

	// If /etc/hyperfocus_distractors exists, take each host from it and append it
	// to /etc/hosts for blocking. Else set distractorsFileWarn to true.
	if fileExists(distractorsFile) {

		distractorsFileObj, err := os.Open(distractorsFile)
		if err != nil {
			log.Fatalln(err)
		}
		defer distractorsFileObj.Close()

		scanner := bufio.NewScanner(distractorsFileObj)
		for scanner.Scan() {
			var hostLine string = fmt.Sprintf("127.0.0.1\t%s\n", scanner.Text())
			if _, err := hostFile.WriteString(hostLine); err != nil {
				log.Fatalln(err)
			}
		}
	} else {
		distractorsFileWarn = true
	}

	// If /etc/hyperfocus_distractors_predefined exists, take each host from it and,
	// append it to /etc/hosts for blocking. Else set predefDistractorsFileWarn to true.
	if fileExists(predefDistractorsFile) {

		predefDistractorsFileObj, err := os.Open(predefDistractorsFile)
		if err != nil {
			log.Fatalln(err)
		}
		defer predefDistractorsFileObj.Close()

		scanner := bufio.NewScanner(predefDistractorsFileObj)
		for scanner.Scan() {
			var hostLine string = fmt.Sprintf("127.0.0.1\t%s\n", scanner.Text())
			if _, err := hostFile.WriteString(hostLine); err != nil {
				log.Fatalln(err)
			}
		}
	} else {
		predefDistractorsFileWarn = true
	}

	// Fail with warning if neither distractors files exist.
	if distractorsFileWarn && predefDistractorsFileWarn {
		log.Fatalln("Error: Please define a set of distractors in your distractors file, one per line.",
			"Alternatively, you can use a predefined set by running `sudo hf predefined`.")
	}

	fmt.Println("Focus is now improved 😊")
}

// Enables access to websites that are defined as 'distractors'
func loseFocus() {

	// Remove the current /etc/hosts file before restoring the backup.
	if err := os.Remove(getHostFile()); err != nil {
		log.Fatalln(err)
	}

	// Restore the backup of /etc/hosts
	if err := copyFile(hostBackupFile, getHostFile()); err != nil {
		log.Fatalln(err)
	}

	fmt.Println("Focus is now lost 🤪")
}

// Enables temporarily breaking concentration
func takeBreak(minutes int) {

	fmt.Println()
	fmt.Println("Your (probably) well-deserved break is commencing...")
	loseFocus()

	// Create a channel to receive os.Interrupt signal from user
	c := make(chan os.Signal, 1)
	signal.Notify(c, os.Interrupt)

	// TODO: Read up on Goroutines and channels and figure how to 'pipe' the os.Signal
	// channel to the goroutine below.

	// Prepare channel to receive signal. Sleep for t minus <minutes * 60> seconds,
	// or break the countdown when interrupt signal is received from user, then
	// improve focus again.
	ticker := time.NewTicker(1 * time.Second)
	done := make(chan bool)

	go func() {
		for {
			select {
			case <-done:
				return
			case t := <-ticker.C:
				// TODO: Figure how to get the number of seconds as integers from t
				fmt.Println(t)
			case <-c:
				return
			}
		}
	}()

	time.Sleep(time.Duration(minutes*60) * time.Second)
	ticker.Stop()
	done <- true

	improveFocus()
	fmt.Println("Welcome back to hyperfocus mode 😊 ")
}

// Prints the current list of distractors to be blocked
func listDistractors() {

	for _, v := range []string{distractorsFile, predefDistractorsFile} {

		userDistractorsFile, err := os.Open(v)
		if err != nil {
			fmt.Println(err)
		}
		defer userDistractorsFile.Close()

		scanner := bufio.NewScanner(userDistractorsFile)

		for scanner.Scan() {
			fmt.Println(scanner.Text())
		}
	}

}

// Adds predefined distractors to .hyperfocus_distractors file
func addPredefinedDistractors() {

	distractors := []string{
		"anandtech.com",
		"answerbag.com",
		"arstechnica.com",
		"awkwardfamilyphotos.com",
		"bbc.com",
		"befunky.com",
		"break.com",
		"buzzfeed.com",
		"cheezburger.com",
		"cnet.com",
		"cnn.com",
		"cracked.com",
		"digg.com",
		"digitaltrends.com",
		"distrowatch.com",
		"ebay.com",
		"engadget.com",
		"everypoet.com",
		"facebook.com",
		"failblog.com",
		"fark.com",
		"firstpost.com",
		"flyertalk.com",
		"fmylife.com",
		"fox.com",
		"freerice.com",
		"gawker.com",
		"geek.com",
		"gizmag.com",
		"gizmodo.com",
		"gsmarena.com ",
		"homestarrunner.com",
		"hulu.com",
		"imgur.com",
		"imore.com",
		"instagram.com",
		"iwastesomuchtime.com",
		"lifehacker.com",
		"liveplasma.com",
		"lunchtimers.com",
		"mashable.com",
		"mcsweeneys.net",
		"medium.com",
		"meetup.com",
		"mono-1.com",
		"myparentsjoinedfacebook.com",
		"myspace.com",
		"netflix.com",
		"news.anandtech.com",
		"news.arstechnica.com",
		"news.buzzfeed.com",
		"news.cheezburger.com",
		"news.cnet.com",
		"news.cracked.com",
		"news.distrowatch.com",
		"news.ebay.com",
		"news.facebook.com",
		"news.gizmodo.com",
		"news.homestarrunner.com",
		"news.imgur.com",
		"news.lifehacker.com",
		"news.meetup.com",
		"news.myspace.com",
		"news.reddit.com",
		"news.sciencemag.org",
		"news.slashdot.com",
		"news.slashdot.org",
		"news.stripgenerator.com",
		"news.theverge.com",
		"news.trulia.com",
		"news.typepad.com",
		"news.ycombinator.com",
		"news.ycombinator.com",
		"news.yelp.com",
		"news.youtube.com",
		"notalwaysright.com",
		"omegle.com",
		"opentable.com",
		"passiveaggressivenotes.com",
		"pcworld.com",
		"petsinclothes.com",
		"phoronix.com",
		"pinterest.com",
		"pogo.com",
		"popurls.com",
		"postsecret.com",
		"realclearpolitics.com",
		"realtor.com",
		"reddit.com",
		"redfin.com",
		"sciencemag.org",
		"sho.com",
		"slashdot.com",
		"slashdot.org",
		"slickdeals.net",
		"stripgenerator.com",
		"techcrunch.com",
		"technorati.com",
		"techradar.com",
		"techrepublic.com",
		"textsfromlastnight.com",
		"thenextweb.com",
		"thepointsguy.com",
		"theverge.com",
		"tomshardware.com",
		"trulia.com",
		"tumblr.com",
		"twitter.com",
		"twitterfall.com",
		"typepad.com",
		"wearables.com",
		"wired.com",
		"woot.com",
		"xkcd.com",
		"yelp.com",
		"youtube.com",
		"zdnet.com",
		"zillow.com",
	}

	predefDistractorsFileObj, err := os.OpenFile(predefDistractorsFile, os.O_CREATE|os.O_WRONLY, 0666)
	if err != nil {
		log.Fatalln(err)
	}
	defer predefDistractorsFileObj.Close()

	dataWriter := bufio.NewWriter(predefDistractorsFileObj)

	for _, v := range distractors {

		_, _ = dataWriter.WriteString(v + "\n")
	}
	dataWriter.Flush()
}

func main() {

	parser := argparse.NewParser("hf", "Block distracting websites and hyperfocus on your work")

	improveCmd := parser.NewCommand("improve", "Improve focus, block the distractors")
	loseCmd := parser.NewCommand("lose", "Lose focus, unblock the distractors")

	breakCmd := parser.NewCommand("break", "Take a break for a number of minutes")
	minutesForBreak := breakCmd.Int("", "minutes", &argparse.Options{Help: "Number of minutes to break for."})

	listCmd := parser.NewCommand("list", "List the distractors defined in the block file (/etc/hyperfocus_distractors)")
	predefinedCmd := parser.NewCommand("predefined", "Add predefined set of distractors to block file")

	if isRoot() {

		err := parser.Parse(os.Args)
		if err != nil {
			fmt.Print(parser.Usage(err))
		}

		if improveCmd.Happened() {
			improveFocus()
		} else if loseCmd.Happened() {
			loseFocus()
		} else if breakCmd.Happened() {
			takeBreak(*minutesForBreak)
		} else if listCmd.Happened() {
			listDistractors()
		} else if predefinedCmd.Happened() {
			addPredefinedDistractors()
		} else {
			fmt.Println("Enter a subcommand; use --help or -h for details.")
		}
	} else {
		fmt.Println("Super user not detected. This program requires root privileges; please re-run with sudo or become root.")
	}
}