package main

import (
	"errors"
	"flag"
	"fmt"
	"os"
	"os/exec"
	"strings"
	"text/template"
	"time"
)

type LicensingData struct {
	ProgramName string
	AuthorName  string
	AuthorEmail string
	Year        int
}

func getGitUser() (string, string, error) {
	var userData [2]string
	for i, v := range []string{"user.name", "user.email"} {
		cmd := exec.Command("git", "config", "--get", v)
		out, err := cmd.Output()
		if err != nil {
			return "", "", errors.New("Can't read Git config")
		}

		userData[i] = strings.TrimSpace(string(out))
	}

	return userData[0], userData[1], nil
}

func getLicenseList() []string {
	d, err := os.Open("templates")
	if err != nil {
		panic(err)
	}
	files, err := d.Readdir(0)
	if err != nil {
		panic(err)
	}

	var lcnsList []string
	for _, v := range files {
		lcnsList = append(lcnsList, strings.Replace(v.Name(), ".template", "", 1))
	}

	return lcnsList
}

func main() {
	OutputFile := flag.String("output", "LICENSE", "Specify different output file")
	License := flag.String("license", "", "Choose a license")
	ProgramName := flag.String("program", "", "Choose a program name")
	authorName := flag.String("name", "", "Set the author name")
	authorEmail := flag.String("email", "", "Set the author email")

	ListTemplates := flag.Bool("list", false, "List available licenses")

	flag.Parse()

	if *ListTemplates {
		fmt.Println(strings.Join(getLicenseList(), ", "))
		return
	}

	if *License == "" {
		fmt.Printf(
			"Error: No license specified\n\nUse --license LICENSE\n\nAvailable licenses:\n%s\n",
			strings.Join(getLicenseList(), ", "),
		)
		return
	}

	tmplFile := "templates/" + *License + ".template"
	tmpl, err := template.ParseFiles(tmplFile)
	if err != nil {
		fmt.Printf("Error: There is no '%s' license\n", *License)
		return
	}

	if *authorName == "" || *authorEmail == "" {
		*authorName, *authorEmail, err = getGitUser()
		if err != nil {
			fmt.Printf(
				"Error: Can't read Git config.\n\nUse --name \"NAME\" and --email EMAIL instead.\n",
			)
			return
		}
	}

	licenseData := LicensingData{
		ProgramName: *ProgramName,
		AuthorName:  *authorName,
		AuthorEmail: *authorEmail,
		Year:        time.Now().Year(),
	}

	outFile, err := os.Create(*OutputFile)
	if err != nil {
		panic(err)
	}
	defer outFile.Close()

	err = tmpl.Execute(outFile, licenseData)
	if err != nil {
		panic(err)
	}
}