package main

import (
	"crypto/tls"
	"net/url"
	"log"
	"net"
	"net/http"
	"bufio"
	"os"
	"strconv"
	"fmt"
	"encoding/json"
	"io/ioutil"
	"strings"
	"html"
	"regexp"
)

type Blog struct {
	Id      string  `json:"id"`
	Content string  `json:"content"`
	Date    string  `json:"created_at"`
	Author  Account `json:"account"`
}

type Config struct {
	Listen      string `json:"listen"`
	CertPath    string `json:"cert_path"`
	KeyPath     string `json:"key_path"`
	BaseURL     string `json:"base_url"`
	Title       string `json:"title"`
	HomeMessage string `json:"home_message"`
}

type Account struct {
	Id   string `json:"id"`
	Name string `json:"display_name"`
	Url  string `json:"url"`
}

type Thread struct {
	Ancestors   []Blog `json:"ancestors"`
	Descendants []Blog `json:"descendants"`
}

func main() {
	config := getConfig()

	listener := listen(config.Listen, config.CertPath, config.KeyPath)
	log.Println("Server successfully started")
	log.Println("Server is listening at " + config.Listen)

	serve(listener, config.BaseURL, config.Title, config.HomeMessage)
}

func getConfig() Config {
	configPath := os.Getenv("MASTOGEM_CONFIG_PATH")
	if configPath == "" {
		log.Println("MASTOGEM_CONFIG_PATH was not set, using default settings")

		config := Config{
			Listen: "127.0.0.1:1965",
			CertPath: "cert.pem",
			KeyPath: "key.rsa",
			BaseURL: "https://mamot.fr",
			Title: "MastoGem",
			HomeMessage: "Welcome on MastoGem, this is a Mastodon proxy for Gemini. You can view the last 20 toots of a Mastodon account by providing its ID.",
		}

		return config
	}

	configFile, err := ioutil.ReadFile(configPath)
	if err != nil {
		log.Fatalln("config file: %s", err)
	}

	var config Config

	json.Unmarshal(configFile, &config)

	return config
}

func listen(address, certFile, keyFile string) net.Listener {
	cert, err := tls.LoadX509KeyPair(certFile, keyFile)
	if err != nil {
		log.Fatalln("loadkeys: %s", err)
	}
	config := &tls.Config{
		ClientAuth:   tls.RequestClientCert,
		Certificates: []tls.Certificate{cert},
		MinVersion:   tls.VersionTLS12,
		InsecureSkipVerify: true,
	}

	listener, err := tls.Listen("tcp", address, config)
	if err != nil {
		log.Fatalln("failed to listen on 0.0.0.0:1965: %s", err)
	}

	return listener
}

func serve(listener net.Listener, baseURL, title, home_message string) {
	for {
		conn, err := listener.Accept()
		if err != nil {
			log.Println(err)
		}

		go handleConn(conn.(*tls.Conn), baseURL, title, home_message)
	}
}

func getRawURL(conn *tls.Conn) (string, error) {
	scanner := bufio.NewScanner(conn)
	if ok := scanner.Scan(); !ok {
		return "", scanner.Err()
	}

	rawURL := scanner.Text()
	if strings.Contains(rawURL, "://") {
		return rawURL, nil
	}

	return fmt.Sprintf("gemini://%s", rawURL), nil
}

func getPath(conn *tls.Conn) (string, error) {
	rawURL, err := getRawURL(conn)
	if err != nil {
		return "", err
	}

	parsedURL, err := url.Parse(rawURL)
	if err != nil {
		return "", err
	}

	return parsedURL.Path, nil
}

func handleConn(conn *tls.Conn, baseURL, title, home_message string) {
	defer conn.Close()

	path, err := getPath(conn)
	if err != nil {
		log.Println("get url: %s", err)
		_, err = fmt.Fprintf(conn, "59 Can't parse request\r\n")
		if err != nil {
			log.Println("send error: %s", err)
			return
		}
		return
	}

	// home
	if path == "" || path == "/" {
		_, err = fmt.Fprintf(conn, "20 text/gemini\r\n# " + title + "\n\n" + home_message)
		if err != nil {
			log.Println("send error: %s", err)
			return
		}
		return
	}

	// profile
	if strings.HasPrefix(path, "/profile/") {
		// skip prefix
		path = path[8:]
		_, err = strconv.ParseUint(path, 10, 64)
		if err != nil {
			log.Println("invalid request: %s", err)
			_, err = fmt.Fprintf(conn, "59 Can't parse request\r\n")
			if err != nil {
				log.Println("send error: %s", err)
				return
			}
			return
		}

		log.Println("Received request for account " + path)

		printProfile(conn, baseURL, path)
	} /* thread */ else if strings.HasPrefix(path, "/thread/") {
		// skip prefix
		path = path[7:]

		_, err = strconv.ParseUint(path, 10, 64)
		if err != nil {
			log.Println("invalid request: %s", err)
			_, err = fmt.Fprintf(conn, "59 Can't parse request\r\n")
			if err != nil {
				log.Println("send error: %s", err)
				return
			}
			return
		}

		log.Println("Received request for thread " + path)

		printThread(conn, baseURL, path)
	} else {
		_, err = fmt.Fprintf(conn, "59 Invalid request\r\n")
		if err != nil {
			log.Println("send: %s", err)
			return
		}
	}
}

func printProfile(conn *tls.Conn, baseURL, profileID string) {
	account, err := getAccount(baseURL, profileID)
	blogs := getBlog(baseURL, profileID)

	if err != nil || blogs == nil {
		_, err = fmt.Fprintf(conn, "40 Remote mastodon instance failed\r\n")
		if err != nil {
			log.Println("handleConn: %s", err)
			return
		}
		return
	}

	_, err = fmt.Fprintf(conn, "20 text/gemini\r\n# Toots for " + account.Name + " account\n")
	if err != nil {
		log.Println("handleConn: %s", err)
		return
	}

	for _, blog := range blogs {
		date := "\n```\n* Posted at " + blog.Date + " *\n```\n"

		text := removeHTMLTags(blog.Content) + "\n"

		_, err = fmt.Fprintf(conn, date + text + "=> /thread/" + blog.Id + " View the thread\n")
		if err != nil {
			log.Println("read blogs: %s", err)
			return
		}
	}

	_, err = fmt.Fprintf(conn, "=> " + account.Url + " Go to " + account.Name + " account")
	if err != nil {
		log.Println("add link: %s", err)
		return
	}
}

func printThread(conn *tls.Conn, baseURL, tootID string) {
	originalToot, err := getToot(baseURL, tootID)
	if err != nil {
		_, err = fmt.Fprintf(conn, "40 Remote mastodon instance failed\r\n")
		if err != nil {
			log.Println("handleConn: %s", err)
			return
		}
		return
	}

	thread, err := getThread(baseURL, tootID)
	if err != nil {
		_, err = fmt.Fprintf(conn, "40 Remote mastodon instance failed\r\n")
		if err != nil {
			log.Println("handleConn: %s", err)
			return
		}
		return
	}

	// Print header
	_, err = fmt.Fprintf(conn, "20 text/gemini\r\n# Ancestors\n")
	if err != nil {
		log.Println("handleConn: %s", err)
		return
	}

	// Print each anscestor
	for _, toot := range thread.Ancestors {
		_, err = fmt.Fprintf(conn, "\n```\n* Posted on " + toot.Date + " by " + toot.Author.Name + " *\n```\n" + removeHTMLTags(toot.Content) + "\n=> /profile/" + toot.Author.Id + " More toots from " + toot.Author.Name + "\n")
		if err != nil {
			log.Println("handleConn: %s", err)
			return
		}
	}

	// Print original toot
	_, err = fmt.Fprintf(conn, "\n# Toot\n\n```\n* Posted on " + originalToot.Date + " by "+ originalToot.Author.Name +" *\n```\n" + removeHTMLTags(originalToot.Content) + "\n=> /profile/" + originalToot.Author.Id + " More toots from " + originalToot.Author.Name + "\n")
	if err != nil {
		log.Println("handleConn: %s", err)
		return
	}

	// Print each descendant
	_, err = fmt.Fprintf(conn, "\n# Descendants\n")
	if err != nil {
		log.Println("handleConn: %s", err)
		return
	}
	for _, toot := range thread.Descendants {
		_, err = fmt.Fprintf(conn, "\n```\n* Posted on " + toot.Date + " by " + toot.Author.Name + " *\n```\n" + removeHTMLTags(toot.Content) + "\n=> /profile/" + toot.Author.Id + " More toots from " + toot.Author.Name + "\n")
		if err != nil {
			log.Println("handleConn: %s", err)
			return
		}
	}
}

func removeHTMLTags(content string) string {
	text := strings.ReplaceAll(content, "<p>", "")
	text = strings.ReplaceAll(text, "</p>", "\n\n")
	text = strings.ReplaceAll(text, "<br />", "\n")
	text = strings.ReplaceAll(text, "<br>", "\n")
	text = strings.ReplaceAll(text, "</a>", "")
	text = strings.ReplaceAll(text, "</span>", "")
	regexString := "<a( [^>]*)?>"
	regex, err := regexp.Compile(regexString)
	if err != nil {
		log.Println("regex: %s", err)
		return ""
	}
	text = regex.ReplaceAllLiteralString(text, "")
	regexString = "<span( [^>]*)?>"
	regex, err = regexp.Compile(regexString)
	if err != nil {
		log.Println("regex: %s", err)
		return ""
	}
	text = regex.ReplaceAllLiteralString(text, "")
	text = html.UnescapeString(text)

	return text
}

func getBlog(baseURL, account string) []Blog {
	if baseURL == "" || account == "" {
		log.Println("baseURL or account is empty")
		return nil
	}

	resp, err := http.Get(baseURL + "/api/v1/accounts/" + account + "/statuses?exclude_reblogs=true&exlude_replies=true")
	if err != nil {
		log.Println("Mastodon API request: %s", err)
		return nil
	}

	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		log.Println("Mastodon API response: %s", resp.Status)
		return nil
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Println("Mastodon response body: %s", err)
	}

	var blogs []Blog
	json.Unmarshal(body, &blogs)

	return blogs
}

func getAccount(baseURL, accountId string) (Account, error) {
	if baseURL == "" || accountId == "" {
		log.Println("baseURL or account is empty")
		return Account{}, fmt.Errorf("baseURL or account is empty")
	}

	resp, err := http.Get(baseURL + "/api/v1/accounts/" + accountId)
	if err != nil {
		log.Println("Mastodon API request: %s", err)
		return Account{}, fmt.Errorf("API request failed")
	}

	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		log.Println("Mastodon API response: %s", resp.Status)
		return Account{}, fmt.Errorf("API response is not 200")
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Println("Mastodon response body: %s", err)
		return Account{}, fmt.Errorf("Failed to read response")
	}

	var account Account
	json.Unmarshal(body, &account)

	return account, nil
}

func getToot(baseURL, tootId string) (Blog, error) {
	if baseURL == "" || tootId == "" {
		log.Println("baseURL or tootID is empty")
		return Blog{}, fmt.Errorf("baseURL or tootID is empty")
	}

	resp, err := http.Get(baseURL + "/api/v1/statuses/" + tootId)
	if err != nil {
		log.Println("Mastodon API request: %s", err)
		return Blog{}, fmt.Errorf("API request failed")
	}

	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		log.Println("Mastodon API response: %s", resp.Status)
		return Blog{}, fmt.Errorf("API response is not 200")
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Println("Mastodon response body: %s", err)
		return Blog{}, fmt.Errorf("Failed to read response")
	}

	var toot Blog
	json.Unmarshal(body, &toot)

	return toot, nil
}

func getThread(baseURL, tootId string) (Thread, error) {
	if baseURL == "" || tootId == "" {
		log.Println("baseURL or tootID is empty")
		return Thread{}, fmt.Errorf("baseURL or tootID is empty")
	}

	resp, err := http.Get(baseURL + "/api/v1/statuses/" + tootId + "/context")
	if err != nil {
		log.Println("Mastodon API request: %s", err)
		return Thread{}, fmt.Errorf("API request failed")
	}

	defer resp.Body.Close()

	if resp.StatusCode != 200 {
		log.Println("Mastodon API response: %s", resp.Status)
		return Thread{}, fmt.Errorf("API response is not 200")
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		log.Println("Mastodon response body: %s", err)
		return Thread{}, fmt.Errorf("Failed to read response")
	}

	var thread Thread
	json.Unmarshal(body, &thread)

	return thread, nil
}