main.go

package main

import (
	"bytes"
	"encoding/json"
	"fmt"
	"log"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/mmcdole/gofeed"
)

var historyPath = "./histories/"

type DiscordPayload struct {
	Content string `json:"content"`
}

func fetchRssItems(rssUrl string) ([]*gofeed.Item, error) {
	fp := gofeed.NewParser()
	feed, err := fp.ParseURL(rssUrl)
	if err != nil {
		log.Printf("Warning: Failed to parse RSS Url, %v", err)
		return nil, err
	}

	if len(feed.Items) == 0 {
		return nil, nil
	}
	return feed.Items, nil

}

func isNewItem(item gofeed.Item, fname string) (bool, error) {
	bytes, err := os.ReadFile(historyPath + fname)
	if err != nil {
		log.Printf("Error: Failed to read %v, %v", historyPath+fname, err)
		return false, err
	}
	// 新着コンテンツ
	if string(bytes) != item.Link {
		return true, nil
	} else {
		return false, nil
	}

}

func SendToDiscord(item *gofeed.Item, webHookUrls []string) error {
	author := ""
	if item.Authors != nil {
		author = "**" + item.Authors[0].Name + "**"
	}
	content := fmt.Sprintf("new post from %s: %s", author, item.Link)
	payload := DiscordPayload{Content: content}
	b, _ := json.Marshal(payload)
	for _, url := range webHookUrls {
		resp, err := http.Post(url, "application/json", bytes.NewBuffer(b))
		if err != nil {
			log.Printf("Warning: Failed to fetch RSS, %v", err)
		}
		defer resp.Body.Close()
	}
	return nil
}

func main() {
	config := ParseConfig()
	log.Println("Info: Starting rss2discord...")
	_, err := os.Stat("./histories")
	if err != nil {
		os.Mkdir("./histories", os.ModePerm)
	}
	for {
		var items = map[string][]*gofeed.Item{}
		for _, rssUrl := range config.RssSourceUrls {
			url, _ := url.Parse(rssUrl)
			hostname := url.Host
			path := url.Path
			fname := hostname + strings.ReplaceAll(path, "/", "-")
			fname = strings.ReplaceAll(fname, ".", "-")
			_, err := os.Stat(historyPath + fname)
			// Not exists
			if err != nil {
				os.WriteFile(historyPath+fname, []byte(""), 0666)
			}
			items[rssUrl], err = fetchRssItems(rssUrl)
			if err != nil || items[rssUrl] != nil {
				log.Printf("Warning: Failed to fetch RSS, %v", err)
				continue
			}
			latestItem := items[rssUrl][0]
			flag, err := isNewItem(*latestItem, fname)
			if err != nil {
				log.Printf("Warning: Failed to check item, %v", err)
			}
			if flag {
				log.Printf("Info: New post coming!: %v %v", latestItem.Content, latestItem.Link)
				SendToDiscord(latestItem, config.WebhookUrls)

				os.WriteFile(historyPath+fname, []byte(latestItem.Link), 0666)
			} else {
				log.Println("Info: No new post, skipping.")
			}

		}
		time.Sleep(time.Duration(config.FetchIntervalMin * int(time.Minute)))
	}
}