package main

import (
	"encoding/base64"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"path"
	"strings"

	"willnorris.com/go/webmention"
)

func main() {
	lastArticleDir, lastArticleDirSet := os.LookupEnv("LAST_ARTICLE_DIR")
	if lastArticleDirSet {
		http.HandleFunc("/hook", func(w http.ResponseWriter, r *http.Request) {
			if r.Method != http.MethodPost {
				http.Error(w, "Wrong HTTP method", http.StatusMethodNotAllowed)
				return
			}

			blacklist := r.URL.Query()["blacklist"]

			feeds, feedsPresent := r.URL.Query()["feed"]
			if feedsPresent {
				go func() {
					for _, feed := range feeds {
						fmt.Println("Check webmentions for feed:", feed)
						article, err := LatestArticle(feed)
						if err != nil {
							fmt.Println(err.Error())
							continue
						}
						lastArticleUrl, lastArticleDate := lastArticle(lastArticleDir, feed)
						if lastArticleUrl != article.Url || lastArticleDate != article.Modified {
							err := sendWebmentions(article.Url, blacklist)
							if err != nil {
								fmt.Println(err.Error())
								continue
							}
							err = updateLastArticle(lastArticleDir, feed, article.Url, article.Modified)
							if err != nil {
								fmt.Println(err.Error())
								continue
							}
						} else {
							fmt.Println("No new article")
							continue
						}
					}
				}()
			}

			urls, urlsPresent := r.URL.Query()["url"]
			if urlsPresent {
				go func() {
					for _, url := range urls {
						fmt.Println("Check webmentions for url:", url)
						err := sendWebmentions(url, blacklist)
						if err != nil {
							fmt.Println(err.Error())
							continue
						}
					}
				}()
			}

		})
		log.Fatal(http.ListenAndServe(":8080", nil))
	} else {
		log.Fatal("Not configured")
	}
}

func lastArticle(dirname string, feed string) (url string, date string) {
	fileContent, _ := ioutil.ReadFile(path.Join(dirname, base64.StdEncoding.EncodeToString([]byte(feed))))
	if len(string(fileContent)) == 0 {
		return
	}
	urlDate := strings.SplitN(string(fileContent), ";", 2)
	return urlDate[0], urlDate[1]
}

func updateLastArticle(dirname string, feed string, url string, date string) error {
	return ioutil.WriteFile(path.Join(dirname, base64.StdEncoding.EncodeToString([]byte(feed))), []byte(url+";"+date), 0644)
}

func sendWebmentions(url string, blacklist []string) error {
	req, err := http.NewRequest(http.MethodGet, url, nil)
	if err != nil {
		return err
	}
	req.Header.Add("User-Agent", "WebmentionHelper")
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	discovered, err := webmention.DiscoverLinksFromReader(resp.Body, url, ".h-entry")
	_ = resp.Body.Close()
	if err != nil {
		return err
	}
	var filtered []string
	allowed := func(link string) bool {
		for _, black := range blacklist {
			if strings.Contains(link, black) {
				return false
			}
		}
		return true
	}
	for _, link := range discovered {
		if allowed(link) {
			filtered = append(filtered, link)
		}
	}
	client := webmention.New(nil)
	for _, link := range filtered {
		endpoint, err := client.DiscoverEndpoint(link)
		if err != nil || len(endpoint) < 1 {
			continue
		}
		_, err = client.SendWebmention(endpoint, url, link)
		if err != nil {
			log.Println("Sending webmention to " + link + " failed")
			continue
		}
		fmt.Println("Sent webmention to " + link)
	}
	return nil
}