package main

import (
	"archive/zip"
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"os"
	"os/user"
	"path"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/gocolly/colly"
	"github.com/schollz/progressbar/v3"
)

type Cache struct {
	MostRecent string
	Pages      int
}

var cacheFile = "~/.taldl.json"

var outputDir = flag.String("output", "~/TAL", "output directory")
var formats = flag.String("formats", "zip,epub,pdf,a4.pdf,lt.pdf", "formats to download")
var progress = flag.Bool("progress", true, "show progress bar")
var verbose = flag.Bool("verbose", true, "verbose output")
var workers = flag.Int("workers", 5, "amount of workers")
var update = flag.Bool("update", false, "update all entries")

var mostRecent string
var done bool
var cache Cache
var useFormat map[string]bool

func main() {
	var bar *progressbar.ProgressBar
	var lastPage int
	var hrefs = []string{}
	var hrefsMutex sync.Mutex
	var done bool

	flag.Parse()

	useFormat = make(map[string]bool)
	fmts := strings.Split(*formats, ",")
	for _, f := range fmts {
		useFormat[f] = true
	}

	cacheFile = fixPath(cacheFile)
	cacheData, _ := ioutil.ReadFile(cacheFile)
	_ = json.Unmarshal(cacheData, &cache)

	*outputDir = fixPath(*outputDir)

	os.MkdirAll(*outputDir, os.ModePerm)

	c := colly.NewCollector()
	c.OnHTML("ul.pagination li:nth-last-child(2)", func(e *colly.HTMLElement) {
		lastPage, _ = strconv.Atoi(strings.TrimSpace(e.Text))
	})
	c.OnHTML("div.amw-listing-item:nth-child(1) a[href]", func(e *colly.HTMLElement) {
		href := e.Attr("href")
		mostRecent = href
	})
	c.OnHTML("div.amw-listing-item a[href]", func(e *colly.HTMLElement) {
		href := e.Attr("href")
		if cache.MostRecent == href {
			done = true
		}
		if !done || *update {
			hrefs = append(hrefs, href)
		}
	})

	url := "https://theanarchistlibrary.org/latest/1"
	c.Visit(url)

	newPages := 1

	if *update {
		newPages = lastPage
	} else {
		newPages = lastPage - cache.Pages
	}

	if newPages > 0 {
		if *verbose {
			fmt.Fprintf(os.Stderr, "Checking latest entries... \r\n")
		}

		if *progress {
			bar = progressbar.Default(int64(newPages))
			bar.Add(1)
		}
	}

	scanJobs := make(chan int, newPages)
	scanResults := make(chan []string, newPages)

	for w := 1; w <= *workers; w++ {
		go scanner(w, scanJobs, scanResults)
	}
	for a := 2; a <= newPages; a++ {
		scanJobs <- a
	}
	close(scanJobs)

	for a := 2; a <= newPages; a++ {
		result := <-scanResults
		hrefsMutex.Lock()
		hrefs = append(hrefs, result...)
		hrefsMutex.Unlock()
		if *progress {
			bar.Add(1)
		}
	}
	close(scanResults)

	cache.Pages = lastPage
	cache.MostRecent = mostRecent

	numJobs := len(hrefs)

	if numJobs == 0 {
		save(cache)
		return
	}

	if *verbose {
		fmt.Fprintf(os.Stderr, "Checking %d entries for updates...\r\n", numJobs)
	}

	if *progress {
		bar = progressbar.Default(int64(numJobs))
		bar.ChangeMax(numJobs)
	}

	checkJobs := make(chan string, numJobs)
	checkResults := make(chan string, numJobs)
	downloadJobs := make(chan string, numJobs)
	downloadResults := make(chan string, numJobs)
	downloadCount := 0

	for w := 1; w <= *workers; w++ {
		go checker(w, checkJobs, checkResults)
	}
	for _, href := range hrefs {
		checkJobs <- href
	}
	close(checkJobs)

	for a := 1; a <= numJobs; a++ {
		r := <-checkResults
		if *progress {
			bar.Add(1)
		}
		if r != "" {
			downloadJobs <- r
			downloadCount++
		}
	}
	close(checkResults)
	close(downloadJobs)

	if downloadCount == 0 {
		save(cache)
		return
	}

	if *verbose {
		fmt.Fprintf(os.Stderr, "Downloading %d entries...\r\n", downloadCount)
	}

	if *progress {
		bar = progressbar.Default(int64(downloadCount))
	}

	for w := 1; w <= *workers; w++ {
		go downloader(w, downloadJobs, downloadResults)
	}

	buffer := ""

	for a := 1; a <= downloadCount; a++ {
		r := <-downloadResults
		if *progress {
			bar.Add(1)
		}
		if r != "" {
			buffer += r
		}
	}
	close(downloadResults)

	save(cache)

	if buffer != "" {
		if *verbose {
			fmt.Fprintln(os.Stderr, buffer)
		}
	}
}

func fixPath(path string) string {
	path = filepath.FromSlash(path)
	if (path)[0] == '~' {
		user, err := user.Current()
		if err != nil {
			fmt.Fprintln(os.Stderr, err.Error())
			os.Exit(10)
		}
		path = filepath.Join(user.HomeDir, (path)[1:])
	}
	path, _ = filepath.Abs(path)
	return path
}

func filenameForUrl(url string) string {
	return path.Base(url)
}

func check(url string, path string, timeout time.Duration) (modified bool, err error) {
	request, err := http.NewRequest("HEAD", url, nil)
	if err != nil {
		return
	}

	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()

	request = request.WithContext(ctx)

	response, err := http.DefaultClient.Do(request)
	if err != nil {
		return
	}
	defer response.Body.Close()

	if response.StatusCode == 404 {
		return false, nil
	}

	if response.StatusCode != 200 {
		return false, fmt.Errorf("%s: %s", url, response.Status)
	}

	lmh := response.Header.Get("Last-Modified")
	lm, err := http.ParseTime(lmh)
	if err != nil {
		return true, err
	}

	file, err := os.Stat(path)
	if err != nil {
		return true, nil
	}

	clh := response.Header.Get("Content-Length")
	cl, err := strconv.ParseInt(clh, 10, 0)
	if err != nil {
		return true, nil
	}

	if file.Size() != cl {
		return true, nil
	}

	if lm.After(file.ModTime()) {
		return true, nil
	}

	return false, nil
}

func get(url string, timeout time.Duration) (content []byte, err error) {
	request, err := http.NewRequest("GET", url, nil)
	if err != nil {
		return
	}

	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()

	request = request.WithContext(ctx)

	response, err := http.DefaultClient.Do(request)
	if err != nil {
		return
	}
	defer response.Body.Close()

	if response.StatusCode == 404 {
		return
	}

	if response.StatusCode != 200 {
		return nil, fmt.Errorf("%s: %s", url, response.Status)
	}

	return ioutil.ReadAll(response.Body)
}

func fileExists(path string) bool {
	info, err := os.Stat(path)
	if os.IsNotExist(err) {
		return false
	}
	return !info.IsDir()
}

func download(url string, path string) (err error) {
	for {
		data, err := get(url, time.Second*60)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: %s: %s\n", url, err)
			time.Sleep(time.Second)
			continue
		}

		err = ioutil.WriteFile(path, data, 0644)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: %s\n", err)
			return err
		}
		break
	}

	return nil
}

func unzip(src string, dest string) ([]string, error) {
	var filenames []string

	r, err := zip.OpenReader(src)
	if err != nil {
		return filenames, err
	}
	defer r.Close()

	for _, f := range r.File {
		fpath := filepath.Join(dest, f.Name)

		if !strings.HasPrefix(fpath, filepath.Clean(dest)+string(os.PathSeparator)) {
			return filenames, fmt.Errorf("%s: bad file path", fpath)
		}

		filenames = append(filenames, fpath)

		if f.FileInfo().IsDir() {
			os.MkdirAll(fpath, os.ModePerm)
			continue
		}

		if err = os.MkdirAll(filepath.Dir(fpath), os.ModePerm); err != nil {
			return filenames, err
		}

		outFile, err := os.OpenFile(fpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, f.Mode())
		if err != nil {
			return filenames, err
		}

		rc, err := f.Open()
		if err != nil {
			return filenames, err
		}

		_, err = io.Copy(outFile, rc)

		outFile.Close()
		rc.Close()

		if err != nil {
			return filenames, err
		}
	}
	return filenames, nil
}

func downloader(id int, jobs <-chan string, results chan<- string) {

	for href := range jobs {
		result := ""
		dir := filenameForUrl(href)
		dest := filepath.Join(*outputDir, dir)
		os.MkdirAll(dest, 0700)

		downloadFormat(href, "zip", dest)
		downloadFormat(href, "epub", dest)
		downloadFormat(href, "pdf", dest)
		downloadFormat(href, "a4.pdf", dest)
		downloadFormat(href, "lt.pdf", dest)

		if *verbose {
			results <- result
		} else {
			results <- ""
		}
	}
}

func scanner(id int, jobs <-chan int, results chan<- []string) {
	var result []string

	c := colly.NewCollector()
	c.OnHTML("div.amw-listing-item a[href]", func(e *colly.HTMLElement) {
		href := e.Attr("href")
		if cache.MostRecent == href {
			done = true
		}
		if !done {
			result = append(result, href)
		}
	})
	c.AllowURLRevisit = true

	for i := range jobs {
		url := fmt.Sprintf("https://theanarchistlibrary.org/latest/%d", i)
		for {
			result = []string{}
			err := c.Visit(url)
			if err != nil {
				fmt.Fprintf(os.Stderr, "error: %s\n", err)
				time.Sleep(time.Second)
			} else {
				break
			}
		}
		results <- result
	}
}

func checker(id int, jobs <-chan string, results chan<- string) {
	var modified bool
	var err error

	for href := range jobs {
		ext := "muse"
		url := href + "." + ext
		dir := filenameForUrl(href)
		name := filenameForUrl(url)
		path := filepath.Join(*outputDir, dir, name)

		if !fileExists(path) {
			results <- href
			continue
		}

		for {
			modified, err = check(url, path, time.Second*30)
			if err != nil {
				fmt.Fprintf(os.Stderr, "error: %s\n", err)
				time.Sleep(time.Second)
				continue
			}
			break
		}

		if modified {
			results <- href
		} else {
			results <- ""
		}
	}
}

func save(cache Cache) {
	cacheData, _ := json.Marshal(&cache)
	_ = ioutil.WriteFile(cacheFile, cacheData, 0644)
}

func downloadFormat(href string, ext string, dest string) error {
	if !useFormat[ext] {
		return nil
	}

	url := href + "." + ext
	name := filenameForUrl(url)

	if ext == "zip" {
		tmpDir, err := ioutil.TempDir(os.TempDir(), "taldl")
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: %s\n", err)
			return err
		}
		path := filepath.Join(tmpDir, name)
		err = download(url, path)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: %s\n", err)
			return err
		}
		_, err = unzip(path, *outputDir)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: %s\n", err)
			return err
		}
		os.RemoveAll(tmpDir)
	} else {
		path := filepath.Join(dest, name)
		err := download(url, path)
		if err != nil {
			fmt.Fprintf(os.Stderr, "error: %s\n", err)
			return err
		}
	}

	return nil
}