tss/app/db.go

package app

import (
	"encoding/csv"
	"errors"
	"fmt"
	"os"
	"path"
	"strings"
	"time"

	"go.balki.me/tss/log"
)

type Status string

const (
	Sent     Status = "SENT"
	Filtered        = "FILTERED"
	Error           = "ERROR"
)

//default format used by yaml.Marshal
const TimeFormat string = "2006-01-02T15:04:05.999999999-07:00"

type Record struct {
	Time      time.Time
	Status    Status
	FeedEntry FeedEntry
}

type DB interface {
	Filter(entries []FeedEntry) ([]FeedEntry, error)
	Save([]Record) error
}

type db struct {
	dbPath    string
	seenLinks map[string]struct{}
}

func NewDB(storageDir, feedName string) (DB, error) {
	dbPath := path.Join(storageDir, fmt.Sprintf("%s.csv", feedName))
	db := db{dbPath: dbPath}
	db.seenLinks = map[string]struct{}{}
	f, err := os.Open(dbPath)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			log.Info("db file does not exist, will be created", "feed", feedName, "path", dbPath)
			return &db, nil
		}
		return nil, err
	}
	defer f.Close()
	reader := csv.NewReader(f)
	records, err := reader.ReadAll()
	if err != nil {
		return nil, fmt.Errorf("failed to parse csv, path:%v, error:%w", dbPath, err)
	}
	for _, rec := range records {
		var recStatus Status = Status(rec[2])
		if recStatus == Sent || recStatus == Filtered {
			db.seenLinks[rec[1]] = struct{}{}
		}
	}
	return &db, nil
}

func (d *db) Filter(entries []FeedEntry) ([]FeedEntry, error) {
	var filteredEntries []FeedEntry
	for _, entry := range entries {
		if _, ok := d.seenLinks[entry.Link]; !ok {
			filteredEntries = append(filteredEntries, entry)
		}
	}
	return filteredEntries, nil
}

func (d *db) Save(records []Record) error {
	f, err := os.OpenFile(d.dbPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		return err
	}
	defer func() {
		f.Sync()
		f.Close()
	}()
	csvw := csv.NewWriter(f)
	if len(d.seenLinks) == 0 { //New file, write header
		csvw.Write([]string{
			"Date",
			"Link",
			"Status",
			"FilteredBy",
			"Content",
		})
	}
	for _, r := range records {
		csvw.Write([]string{
			r.Time.Format(TimeFormat),
			r.FeedEntry.Link,
			string(r.Status),
			"-",
			strings.ReplaceAll(r.FeedEntry.Content, "\n", " "),
		})
	}
	csvw.Flush()
	return nil
}