package main

import (
	"archive/tar"
	"bytes"
	"compress/gzip"
	"flag"
	"fmt"
	"io"
	"io/fs"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"runtime/debug"
	"strings"
	"time"

	"golang.org/x/net/html"
)

var DEBUG = false

/* UserAgent */

// The value I want is (unfortunately) private http.Request.defaultUserAgent
const DefaultUserAgent = "Go-http-client/2.0"

// const UserAgent = "Go-updater/0.1.0"

type AddHeaderTransport struct {
	Transport http.RoundTripper
}

func (adt *AddHeaderTransport) RoundTrip(req *http.Request) (*http.Response, error) {
	req.Header.Set("User-Agent", fmt.Sprintf("Rar-updater/%s %s", buildVersion, DefaultUserAgent))
	return adt.Transport.RoundTrip(req)
}

var client *http.Client

func client_init() {
	client = &http.Client{
		Transport: &AddHeaderTransport{
			Transport: http.DefaultTransport,
		},
	}
}

var buildInfo *debug.BuildInfo
var buildGoVersion, buildVersion string

func init() {
	var ok bool
	buildInfo, ok = debug.ReadBuildInfo()
	if !ok {
		return
	}
	buildVersion = buildInfo.Main.Version
	buildGoVersion = buildInfo.GoVersion
	client_init()
}

// Get go version from the download URL.
//
// /rar/rarlinux-x64-720.tar.gz

func GetVersionFromUrl(url string) string {
	part, _, _ := strings.Cut(url, ".") // /rar/rarlinux-x64-720
	index := strings.LastIndex(part, "-")
	if index != -1 {
		return part[index+1:]
	}
	return ""
}

/*
This is what I'm looking for:

<tr>
  <td><a href="/rar/winrar-x64-720.exe">
  <b>WinRAR x64 (64 bit) 7.20</b></a></td>
  <td>Graphical and command line</td>
  <td align="center">Trial</td>
  <td align="right">3683 KB</td>
</tr>
...
<tr>
  <td><a href="/rar/rarlinux-x64-720.tar.gz">
  <b>RAR for Linux x64 7.20</b></a></td>
  <td>Command line only</td>
  <td align="center">Trial</td>
  <td align="right">728 KB</td>
</tr>
*/

func ParseHtml(read io.Reader, os_arch string) string {
	var tokens = html.NewTokenizer(read)
	var result string
	var arch_link string
	var found_links bool = false
	var done bool = false

tloop:
	for {
		tt := tokens.Next()

		switch tt {
		case html.ErrorToken:
			break tloop

		case html.StartTagToken:
			if done {
				continue
			}

			tn, _ := tokens.TagName()
			if bytes.Equal(tn, []byte("a")) {
				/*
					This is specific to how the HTML is defined.
					If it changes, this will definitely need to be updated.

					We look for class=download with href containing /go.

				*/

				key, value, more := tokens.TagAttr()
				_ = more

				if bytes.Equal(key, []byte("href")) {
					// Does it contain link to go?
					if bytes.Contains(value, []byte("/rar/")) {
						found_links = true
						arch_link = string(value)
						if strings.Contains(arch_link, os_arch) {
							result = arch_link
						}
						if DEBUG {
							// a href=/dl/go1.25.6.linux-amd64.tar.gz
							fmt.Printf("a href=%s\n", value)
						}
					}
				}
			}
		case html.EndTagToken:
			tn, _ := tokens.TagName()
			// fmt.Printf("End token : [%s]\n", tn)

			if bytes.Equal(tn, []byte("table")) {
				if found_links == true {
					done = true
				}
			}
		}

	}
	return result
}

// This function has been fixed.  It works correctly now.

func RelativeToAbsoluteUrl(base string, href string) (string, error) {
	var result string
	base_url, err := url.Parse(base)
	if err != nil {
		fmt.Printf("Failed to parse %s\n", base)
		return result, err
	}
	abs_url, err := base_url.Parse(href)
	if err != nil {
		fmt.Printf("Failed to parse %s\n", href)
		return result, err
	}
	// fmt.Printf("Base %s Href %s => %s\n", base, href, abs_url)
	result = abs_url.String()
	return result, nil
}

// Does this handle read-only?  GOPATH has files marked readonly. :(

// Mark directories as 0755 and files as 0666.
func RemoveReadOnly(dir string) error {
	var err = filepath.Walk(dir, func(path string, info fs.FileInfo, err error) error {
		if err != nil {
			return err
		}

		// var p = info.Mode().Perm()
		if info.IsDir() {
			err = os.Chmod(path, 0755)
			if err != nil {
				return err
			}
		} else {
			// Ok, it's a file then.
			err := os.Chmod(path, 0666)
			if err != nil {
				return err
			}
		}
		return nil
	})
	return err
}

// Remove directory contents
//
// Use this to clear out the GOROOT directory.
// This works, if RemoveReadOnly has been called on the dir.
func RemoveContents(dir string) error {
	d, err := os.Open(dir)
	if err != nil {
		return err
	}
	defer d.Close()
	names, err := d.Readdirnames(-1)
	if err != nil {
		return err
	}
	for _, name := range names {

		err = os.RemoveAll(filepath.Join(dir, name))
		if err != nil {
			return err
		}
	}
	return nil
}

// Convert URL into usable filename for cache.
//
// This looks for the last '/' and uses everything after that
// as the filename.
func UrlToFilename(url string) string {
	var result string
	if strings.HasSuffix(url, "/") {
		url = strings.TrimRight(url, "/")
	}
	idx := strings.LastIndex(url, "/")
	if idx == -1 {
		fmt.Printf("filename from url %s : failed.\n", url)
		os.Exit(10)
	}
	result = url[idx+1:]
	return result
}

/*

fn extract_tarball(tarball: &str, target: &str) -> Result<()> {
    println!("Extract {} to {}", tarball, target);
    let output = Command::new("tar")
        // Extract, gzipped, from file
        .arg("-xzf")
        .arg(tarball)
        // archive contains go directory. Strip that out.
        .arg("--strip-components=1")
        // Set target to extract to.
        .arg("-C")
        .arg(target)
        .output()?;
    if output.status.success() {
        return Ok(());
    }
    bail!("Extract {} failed.", tarball);
}
*/

func ExtractTarball(tarball string, target string) error {
	var cmd = []string{"tar", "-xzf", tarball, "--strip-components=1", "-C", target}
	_, err := exec.Command(cmd[0], cmd[1:]...).Output()
	return err
}

// Expire files from cache over N days old.
func CacheExpire(dir string, days int) (int, error) {
	var result int
	oldDate := time.Now().AddDate(0, 0, -days) // N days ago
	err := filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
		if err != nil {
			return err
		}
		if info.ModTime().Before(oldDate) {
			err := os.Remove(path)
			if err != nil {
				fmt.Println("Error deleting file:", err)
				return err
			} else {
				result += 1
				if DEBUG {
					fmt.Println("Deleted:", path)
				}
			}
		}
		return nil
	})
	return result, err
}

func FindRar() (string, error) {
	return exec.LookPath("rar")
}

func RarVersion() string {
	output, _ := exec.Command("rar").Output()
	// fmt.Printf("RAR:\n%s\n", output)
	buffer := bytes.NewBuffer(output)
	line, err := buffer.ReadString('\n')
	if err != nil {
		return ""
	}
	line, _ = strings.CutSuffix(line, "\n")

	for len(line) == 0 {
		// First line is blank.
		line, err = buffer.ReadString('\n')
		if err != nil {
			return ""
		}
		line, _ = strings.CutSuffix(line, "\n")
	}

	if DEBUG {
		fmt.Printf("RAR: [%s]\n", line)
	}

	if line != "" {
		rarver, _, found := strings.Cut(line, "   ")
		if found {
			line = rarver
		}
	}

	// Ok, we should have something like "RAR 7.10"
	_, version, found := strings.Cut(line, " ")
	if found {
		return version
	}

	return line
}

/*
Tarball /home/thor/.cache/rar-upgrade/rarlinux-x64-720.tar.gz:
Name: unrar Mode 755
Wrote 441632 bytes.
Name: default.sfx Mode 755
Wrote 248960 bytes.
Name: rar Mode 755
Wrote 798760 bytes.
*/

func read_tarball(fp *os.File) {
	// https://gauravgahlot.in/extracting-files-gzipped-tar-archive-go/

	gzipReader, err := gzip.NewReader(fp)
	if err != nil {
		panic(err) // for now
	}
	tarReader := tar.NewReader(gzipReader)

	for {
		header, err := tarReader.Next()
		if err == io.EOF {
			break
		}

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

		if header.Typeflag == tar.TypeReg {
			var basefilename string
			index := strings.LastIndex(header.Name, "/")
			if index != -1 {
				basefilename = header.Name[index+1:]
			} else {
				basefilename = header.Name
			}

			if header.Mode == 0755 {
				// This is an executable, extract it!

				fmt.Printf("Name: %s Mode %o\n", basefilename, header.Mode)
				fpout, err := os.OpenFile(basefilename, os.O_CREATE|os.O_WRONLY, os.FileMode(header.Mode))
				if err != nil {
					panic(err)
				}
				defer fpout.Close()

				size, err := io.Copy(fpout, tarReader)
				if err != nil {
					panic(err)
				} else {
					fmt.Printf("Wrote %d bytes.\n", size)
				}
			}

			// Within the header, you have Name, Mode, UID, GID, etc.
			// fmt.Printf("Header: %+v\n", header)
		}
	}
}

/*
I also would like this program to be able to fresh/new install go!

This would require writing/updating .bash_aliases with:
export GOROOT=$HOME/go
export GOPATH=$HOME/gopath
export PATH=$PATH:$GOROOT/bin:$GOPATH/bin
*/

// Main go download page.
const RAR_URL = "https://www.rarlab.com/download.htm"

// Save html to this filename.
var RAR_URL_FILE = UrlToFilename(RAR_URL)

func main() {
	HOME := os.Getenv("HOME")
	if len(HOME) == 0 {
		fmt.Printf("Expected $HOME environment variable to be set.")
		os.Exit(2)
	}

	CACHE_DIR := fmt.Sprintf("%s/.cache/rar-upgrade", HOME)

	// Display information?
	var (
		info   bool
		stop   bool
		expire int
	)

	flag.BoolVar(&info, "info", false, "Display information")
	flag.BoolVar(&DEBUG, "debug", false, "Debug information")
	flag.IntVar(&expire, "expire", 30, "Number of days to expire")
	flag.BoolVar(&stop, "stop", false, "Stop execution (before fetching anything)")
	flag.Parse()

	if os.Geteuid() == 0 {
		fmt.Println("HEY!  This program should never be run as root.")
		fmt.Println("This program manages a user install of rar (possibly in ~/bin).")
		return
	}

	// Ok, we're not running as root, so we can create/check the cache directory.

	{
		err := os.MkdirAll(CACHE_DIR, 0755)
		if err != nil {
			fmt.Printf("Unable to create cache directory %s: %s\n", CACHE_DIR, err)
			return
		}
	}

	// Expire the cache
	count, ceerr := CacheExpire(CACHE_DIR, expire)
	if ceerr != nil {
		fmt.Printf("CacheExpire error: %s\n", ceerr)
		return
	}
	if count != 0 {
		fmt.Printf("CacheExpire: removed %d file(s).\n", count)
	}

	// Is rar installed?
	rar, rarerr := FindRar()
	var rarversion string

	if rarerr == nil {
		// Ok, rar has been located in the path.
		rarversion = RarVersion()
	}

	var arch_link string

	if info {
		fmt.Printf("RAR @ %s => Version %s\n", rar, rarversion)
		/*
			fmt.Printf("Current version: %s\n", go_version)
			fmt.Printf("OS Arch: %s\n", go_os_arch)

			fmt.Printf("GO ENV:\n%+v\n", goenv)
			fmt.Printf("Built by: %s\n", buildGoVersion)
			fmt.Printf("Go-Update: %s\n", buildVersion)
		*/
	}

	if stop {
		fmt.Println("Ok, parse HTML file:")
		var filename = CACHE_DIR + "/" + RAR_URL_FILE
		var parse_link string
		fp, err := os.Open(filename)
		if err == nil {
			defer fp.Close()
			parse_link = ParseHtml(fp, "linux")
			fmt.Printf("Parse HTML link: %s\n", parse_link)
		} else {
			fmt.Printf("Missing cache file: %s\n", filename)
		}

		// parse_link => /rar/rarlinux-x64-720.tar.gz
		index := strings.LastIndex(parse_link, "/")
		if index != -1 {
			parse_link = parse_link[index+1:]
		}

		filename = CACHE_DIR + "/" + parse_link
		fp, err = os.Open(filename)
		if err == nil {
			defer fp.Close()
			// Ok! We have open tarball file.
			fmt.Printf("Tarball %s:\n", filename)
			read_tarball(fp)
		} else {
			fmt.Printf("Missing cache file: %s\n", filename)
		}

		fmt.Println("Get user-agent string from httpbin site:")
		var resp, _ = client.Get("https://httpbin.org/user-agent")
		defer resp.Body.Close()
		io.Copy(os.Stdout, resp.Body)
		fmt.Println("And we'll stop right here for now...")
		return
	}

	var resp, err = client.Get(RAR_URL)
	if err != nil {
		fmt.Printf("Get %s error: %s\n", RAR_URL, err)
		return
	}
	defer resp.Body.Close()

	// Verify that we got a status 200.

	if resp.StatusCode != 200 {
		fmt.Printf("From %s: %s\n", RAR_URL, resp.Status)
		return
	}

	// Possibly save the header into the cache directory as well.
	// resp.Header

	var filename = CACHE_DIR + "/" + RAR_URL_FILE
	fp, err := os.Create(filename)
	if err != nil {
		fmt.Printf("Create %s failed: %s\n", filename, err)
		return
	}

	fmt.Printf("%s : %s\n", RAR_URL, resp.Status)

	// Read from resp.Body and write it to the filename, and to parse_html.
	var read = io.TeeReader(resp.Body, fp)
	_ = read
	var download_link, rar_version string
	// Remove . from version
	rar_version = strings.ReplaceAll(rarversion, ".", "")

	arch_link = ParseHtml(read, "linux")

	if len(arch_link) == 0 {
		fmt.Printf("I wasn't able to locate the go download URL link for %s.\n", download_link)
		fmt.Printf("Check the file %s, maybe the link has changed?\n", filename)
		return
	}

	dl_version := GetVersionFromUrl(arch_link)
	if dl_version == rar_version {
		fmt.Println("You have the latest version of RAR.")
		return
	}

	fmt.Printf("Version: %s [have %s]\n", dl_version, rar_version)
	var arch_filename = UrlToFilename(arch_link)

	// Download
	//
	var dl_url string
	dl_url, err = RelativeToAbsoluteUrl(RAR_URL, arch_link)
	if err != nil {
		fmt.Printf("URL %s / href %s\n", RAR_URL, arch_link)
		fmt.Printf("Failed converting relative to absolute: %s\n", err)
		return
	}

	fmt.Printf("URL: %s\n", dl_url)

	resp, err = client.Get(dl_url)
	if err != nil {
		fmt.Printf("Get %s error: %s\n", dl_url, err)
		return
	}
	defer resp.Body.Close()

	// Verify that we got a status 200.

	if resp.StatusCode != 200 {
		fmt.Printf("From %s: %s\n", dl_url, resp.Status)
		return
	}

	// I've tried using/setting headers, etc for 304 Not modified, but
	// the website ignores it/doesn't use such things.  Revisit.

	// Save file to cache
	filename = CACHE_DIR + "/" + arch_filename
	fp, err = os.Create(filename)
	if err != nil {
		fmt.Printf("Create %s failed: %s\n", filename, err)
		return
	}

	_, err = io.Copy(fp, resp.Body)
	if err != nil {
		fmt.Printf("Error saving %s\n", err)
		return
	}

	// Unarchive arch_filename into GOROOT.
	fmt.Printf("Extracting %s to %s ...", filename, "DERP")
	// err = ExtractTarball(filename, path)
	fmt.Println()
}