package main

import (
	"bufio"
	"crypto/md5"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"sort"
	"strings"
	"time"

	irc "github.com/fluffle/goirc/client"
	"github.com/mmcdole/gofeed"
)

var (
	server   = flag.String("server", "", "IRC server")
	channel  = flag.String("channel", "", "IRC channel")
	nick     = flag.String("nick", "", "IRC nickname")
	period   = flag.String("period", "10m", "Update period")
	seenPath = flag.String("seen", "", "\"Seen\" entries store")
	postOld  = flag.Bool("post-old", false, "Post all entries on the first fetch ever")
)

func main() {
	flag.Parse()
	if !flag.Parsed() || *server == "" || *channel == "" || *nick == "" || *seenPath == "" || len(flag.Args()) == 0 {
		flag.Usage()
		if flag.Parsed() {
			fmt.Fprintln(os.Stderr, "Flags -server, -channel, -nick and -seen are not optional.")
			fmt.Fprintln(os.Stderr, "At least one url has to be provided.")
		}
		os.Exit(1)
	}

	updatePeriod, err := time.ParseDuration(*period)
	if err == nil && updatePeriod < 5*time.Minute {
		err = fmt.Errorf("too short: %s", updatePeriod)
	}
	if err != nil {
		fmt.Fprintf(os.Stderr, "update period: %s", err)
		os.Exit(1)
	}

	seenFile, err := os.OpenFile(*seenPath, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
	if err != nil {
		fmt.Fprintf(os.Stderr, "seen file: %s", err)
		os.Exit(1)
	}
	defer seenFile.Close()
	seenReader := bufio.NewReader(seenFile)
	seen := make(map[[md5.Size]byte]struct{})
	for {
		if url, err := seenReader.ReadString('\n'); err != nil {
			if errors.Is(err, io.EOF) {
				break
			}
			fmt.Fprintf(os.Stderr, "seen file: %s", err)
			os.Exit(1)
		} else {
			url := []byte(strings.TrimSpace(url))
			seen[md5.Sum(url)] = struct{}{}
		}
	}

	urls := flag.Args()
	skipFirst := make(map[string]struct{})
	if len(seen) == 0 && !*postOld {
		for _, url := range urls {
			skipFirst[url] = struct{}{}
		}
	}

	cfg := irc.NewConfig(*nick, "feed2ircbot", "feed2irc bot")
	c := irc.Client(cfg)
	c.EnableStateTracking()
	c.HandleFunc(irc.CONNECTED, func(*irc.Conn, *irc.Line) {
		log.Printf("irc: connected")
		c.Join(*channel)
	})
	c.HandleFunc(irc.DISCONNECTED, func(*irc.Conn, *irc.Line) {
		log.Printf("irc: disconnected")
		os.Exit(1)
	})

	joinedChan := make(chan bool, 1)
	c.HandleFunc(irc.JOIN, func(c *irc.Conn, line *irc.Line) {
		if c.Me().Nick == line.Nick {
			log.Printf("irc: joined")
			close(joinedChan)
		}
	})
	if err := c.ConnectTo(*server); err != nil {
		fmt.Fprintf(os.Stderr, "irc: %s", err)
		os.Exit(1)
	}

	<-joinedChan
	for {
		for _, url := range urls {
			p := gofeed.NewParser()
			if feed, err := p.ParseURL(url); err != nil {
				log.Printf("%s: %s", url, err)
			} else {
				sort.Sort(feed)
				for _, item := range feed.Items {
					sum := md5.Sum([]byte(item.Link))
					if _, have := seen[sum]; !have {
						if _, err := fmt.Fprintln(seenFile, item.Link); err != nil {
							log.Printf("seen file: %s", err)
							os.Exit(1)
						}
						seenFile.Sync()
						seen[sum] = struct{}{}
						if _, skip := skipFirst[url]; !skip {
							s := fmt.Sprintf("%s | %s\n", item.Title, item.Link)
							c.Privmsgln(*channel, s)
						}
					}
				}
				delete(skipFirst, url)
			}
		}
		time.Sleep(updatePeriod)
	}
}