tss/app/db.go

package app

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

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

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
	Filter    string
	FeedEntry parser.FeedEntry
}

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

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

func (d *db) IsNewFeed() bool {
	return len(d.seenLinks) == 0
}

func NewDB(storageDir, feedName string) (DB, error) {
	dbPath := path.Join(storageDir, fmt.Sprintf("%s.csv", feedName))
	db := db{
		dbPath:    dbPath,
		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 []parser.FeedEntry) ([]parser.FeedEntry, error) {
	var filteredEntries []parser.FeedEntry
	for _, entry := range entries {
		if _, ok := d.seenLinks[entry.Link]; !ok {
			filteredEntries = append(filteredEntries, entry)
			d.seenLinks[entry.Link] = struct{}{}
		}
	}
	return filteredEntries, nil
}

func (d *db) Save(records []Record) error {
	if len(records) == 0 {
		return nil
	}

	f, err := os.OpenFile(d.dbPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
	if err != nil {
		return err
	}
	defer f.Close()

	csvw := csv.NewWriter(f)
	defer csvw.Flush()

	if d.IsNewFeed() {
		csvw.Write([]string{
			/* 1 */ "Date",
			/* 2 */ "Link",
			/* 3 */ "Status",
			/* 4 */ "Filter",
			/* 5 */ "Content",
		})
	}
	for _, r := range records {
		csvw.Write([]string{
			/* 1 */ r.Time.Format(TimeFormat),
			/* 2 */ r.FeedEntry.Link,
			/* 3 */ string(r.Status),
			/* 4 */ r.Filter,
			/* 5 */ fmt.Sprintf("<item>%s</item>", strings.ReplaceAll(r.FeedEntry.Content, "\n", " ")),
		})
	}
	return nil
}