package main

import (
	"bufio"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"regexp"
	"runtime"
	"strconv"
)

const (
	ErrNoCompiler = "none of the following latex compilers available: [latexmk, pdflatex]"
)

func main() {
	fmt.Printf("Pdflatex command exists: %t\n", commandExists("pdflatex"))
	fmt.Printf("LatexMk command exists: %t\n", commandExists("latexmk"))
	fmt.Printf("Operation System: %s/%s\n", runtime.GOOS, runtime.GOARCH)

	compileAndInstall()
}

func compileAndInstall() {
	out, err := compileLatex("main.tex")

	if err != nil {
		fmt.Println("An error occured while compiling the document!")

		if err.Error() == ErrNoCompiler {
			log.Fatal(err.Error())
		}

		if filename := parseMissingFile(out); filename != "" {
			fmt.Printf("We need to download: %s\n", filename)

			// now we need to perform a root check
			if rootCheck() {
				log.Println("Awesome! You are now running this program with root permissions!")

				if installFile(filename) {
					// we remove the main aux file to really trigger a rebuild!
					os.Remove("main.aux")
					// if successfully installed we try to compile again
					compileAndInstall()
				}
			} else {
				log.Fatal("This program must be run as root! (sudo)")
			}
		} else {
			fmt.Println(*out)

			fmt.Println("another build error occured!")
		}
	} else {
		fmt.Println("document built successfully!")
	}
}

func parseMissingFile(output *string) string {
	matchfile := regexp.MustCompile("! LaTeX Error: File `([^`']*)' not found|! I can't find file `([^`']*)'.")
	matches := matchfile.FindStringSubmatch(*output)
	fmt.Printf("%#v\n", matches)
	if matches != nil {
		if matches[1] != "" {
			return matches[1]
		} else {
			return matches[2]
		}
	}

	// ok now we try to find a font error
	fontregex := regexp.MustCompile(`! Font \\[^=]*=([^\s]*)\s`)
	fontmatch := fontregex.FindStringSubmatch(*output)
	fmt.Printf("%#v\n", fontmatch)
	if fontmatch != nil {
		if fontmatch[1] != "" {
			return fontmatch[1]
		}
	}

	// now try babel errors
	babelregex := regexp.MustCompile("Unknown option `([^`']*)'. Either you misspelled")
	babelmatch := babelregex.FindStringSubmatch(*output)
	if babelmatch != nil {
		if babelmatch[1] != "" {
			return babelmatch[1] + ".ldf"
		}
	}

	return ""
}

// check if a specific system command is available
func commandExists(cmd string) bool {
	_, err := exec.LookPath(cmd)
	return err == nil
}

// parse the thumbail picture from video file
func compileLatex(filename string) (*string, error) {
	app := ""
	if commandExists("latexmk") {
		app = "latexmk"
	} else if commandExists("pdflatex") {
		app = "pdflatex"
	} else {
		return nil, fmt.Errorf(ErrNoCompiler)
	}

	cmd := exec.Command(app,
		"-file-line-error",
		"-interaction=nonstopmode",
		"-synctex=1",
		"-output-format=pdf",
		filename)

	stdout, _ := cmd.StdoutPipe()
	stderr, _ := cmd.StderrPipe()

	cmd.Start()

	output := ""

	go func() {
		scanner := bufio.NewScanner(stdout)

		for scanner.Scan() {
			m := scanner.Text()
			output += m + "\n"
			printPoint()
		}
		fmt.Println()
	}()

	go func() {
		scanner := bufio.NewScanner(stderr)
		for scanner.Scan() {
			scanner.Text()
			printPoint()
		}
	}()

	err := cmd.Wait()

	return &output, err
}

var i = 0

func printPoint() {
	if i%10 == 0 {
		fmt.Printf(".")
	}

	i++
	if i > 500 {
		i = 0
		fmt.Println()
	}
}

func rootCheck() bool {
	cmd := exec.Command("id", "-u")
	output, err := cmd.Output()

	if err != nil {
		log.Fatal(err)
	}

	// output has trailing \n
	// need to remove the \n
	// otherwise it will cause error for strconv.Atoi
	// log.Println(output[:len(output)-1])

	// 0 = root, 501 = non-root user
	i, err := strconv.Atoi(string(output[:len(output)-1]))

	if err != nil {
		// maybe no unix system?
		log.Fatal(err)
	}

	return i == 0
}

func installFile(filename string) bool {
	if !commandExists("dnf") {
		fmt.Println("dnf not existing!")
		return false
	}

	cmd := exec.Command("dnf", "-y", "install", fmt.Sprintf("tex(%s)", filename))
	fmt.Println(cmd.String())

	stdout, _ := cmd.StdoutPipe()
	stderr, _ := cmd.StderrPipe()

	fmt.Println("running dnf install now!")
	cmd.Start()

	printReadCloserToStdout(stdout)
	printReadCloserToStdout(stderr)

	err := cmd.Wait()
	if err != nil {
		fmt.Println(err.Error())
		return false
	}
	return true
}

func printReadCloserToStdout(reader io.ReadCloser) {
	go func() {
		scanner := bufio.NewScanner(reader)
		for scanner.Scan() {
			m := scanner.Text()
			fmt.Println(m)
		}
	}()
}