feed-to-muc/getarticles.go

/* Copyright 2018 Martin Dosch
Licensed under the "MIT License" */

package main

import (
	"encoding/json"
	"hash/fnv"
	"log"
	"os"
	"strconv"
	"strings"
	"time"

	"github.com/mmcdole/gofeed"
	"jaytaylor.com/html2text"
)

//func getArticles(max int) ([]string, error) {
func getArticles(feedURL string, max int, cachePath string) (string, error) {

	type feedCache struct {
		LastChange string
	}

	var output string
	var last time.Time
	var lastUpdate feedCache
	var file *os.File
	var updateTime time.Time

	// Create a hash as identifier for the feed.
	// The identifier will be used as filename for caching the update time.
	// ToDo: cachePath should probably be moved to ~/.cache/feed-to-muc
	h := fnv.New32a()
	h.Write([]byte(feedURL))
	cachePath = cachePath + "cache/"
	if _, err := os.Stat(cachePath); os.IsNotExist(err) {
		err = os.MkdirAll(cachePath, 0700)
		if err != nil {
			log.Fatal("Error: ", err)
		}
	}

	cacheFile := cachePath + strconv.Itoa(int(h.Sum32()))

	if _, err := os.Stat(cacheFile); os.IsNotExist(err) {
		file, err = os.Create(cacheFile)
		if err != nil {
			log.Fatal("Error: ", err)
		}
		defer file.Close()

		last = time.Now()

		lastUpdate.LastChange = last.Format(time.RFC3339)

		lastUpdateJSON, _ := json.MarshalIndent(lastUpdate, "", " ")
		_, err = file.Write(lastUpdateJSON)
		if err != nil {
			log.Fatal("Error: ", err)
		}

	} else {

		file, err = os.OpenFile(cacheFile, os.O_RDWR, 0600)
		if err != nil {
			log.Fatal("Error: ", err)
		}
		defer file.Close()

		decoder := json.NewDecoder(file)
		lastUpdate := feedCache{}
		if err := decoder.Decode(&lastUpdate); err != nil {
			log.Fatal("Error: ", err)
		}

		last, err = time.Parse(time.RFC3339, string(lastUpdate.LastChange))
		if err != nil {
			log.Fatal("Error: ", err)
		}
	}

	fp := gofeed.NewParser()
	feed, err := fp.ParseURL(feedURL)
	if err != nil {
		return "", err
	}

	// If no publish date is offered try update date.
	// If both is not offered give up.
	if feed.Items[0].PublishedParsed == nil {
		if feed.Items[0].UpdatedParsed == nil {
			return "", err
		}
		// If cached timestamp is newer than the one of
		// the last article return.
		if last.After(*feed.Items[0].UpdatedParsed) {
			return "", err
		}
	} else {
		// If cached timestamp is newer than the one of
		// the last article return.
		if last.After(*feed.Items[0].PublishedParsed) {
			return "", err
		}
	}

	// Check last n (defined in config) articles for new ones.
	for i := max - 1; i >= 0; i-- {
		// Stop processing for article i if there are not so
		// many articles in the feed.
		if len(feed.Items) < i+1 {
			continue
		}
		article := *feed.Items[i]
		if err != nil {
			return "", err
		}

		if article.PublishedParsed == nil {
			updateTime = *article.UpdatedParsed
		} else {
			updateTime = *article.PublishedParsed
		}

		// If cached timestamp is not older than the article stop processing.
		// Note: Checking for cached timestamp being newer, instead of not older
		// lead to duplicate messages for the same article. Probably a corner
		// case when the time is identical.
		if last.Before(updateTime) == false {
			continue
		}

		if i == 0 {
			last = updateTime
			lastUpdate.LastChange = updateTime.Format(time.RFC3339)

			// Remove file with cached timestamp and create it
			// again with updated timestamp.
			// ToDo: Replace timestamp without deleting.
			err = os.Remove(cacheFile)
			if err != nil {
				log.Fatal("Error: ", err)
			}

			file, err = os.Create(cacheFile)
			if err != nil {
				log.Fatal("Error: ", err)
			}
			defer file.Close()

			lastUpdateJSON, _ := json.MarshalIndent(lastUpdate, "", " ")
			_, err = file.Write(lastUpdateJSON)
			if err != nil {
				log.Fatal("Error: ", err)
			}
		}

		// Strip HTML as we want to get plain text.
		description, err := html2text.FromString(article.Description)
		if err != nil {
			return "", err
		}

		if strings.Contains(description, article.Link) == true {
			output = output + feed.Title + ": *" + article.Title + "*\n\n" + description
		} else {
			output = output + feed.Title + ": *" + article.Title + "*\n\n" + description + "\n" + article.Link
		}

		if i > 0 {
			output = output + "\n\n---\n\n"
		}
	}

	return output, err
}