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package feed
import (
"bufio"
"crypto/sha256"
"encoding/gob"
"errors"
"fmt"
"os"
"time"
"github.com/Necoro/feed2imap-go/internal/log"
)
const (
currentVersion byte = 1
startFeedId uint64 = 1
)
type Cache interface {
findItem(*Feed) CachedFeed
Version() byte
transformToCurrent() (Cache, error)
}
type feedId uint64
type feedDescriptor struct {
Name string
Url string
}
type CachedFeed interface {
Checked(withFailure bool)
Failures() uint
}
type cachedFeed struct {
LastCheck time.Time
NumFailures uint // can't be named `Failures` b/c it'll collide with the interface
Items []cachedItem
}
func (cf *cachedFeed) Checked(withFailure bool) {
cf.LastCheck = time.Now()
if withFailure {
cf.NumFailures++
} else {
cf.NumFailures = 0
}
}
func (cf *cachedFeed) Failures() uint {
return cf.NumFailures
}
type itemHash [sha256.Size]byte
type cachedItem struct {
Uid string
Title string
Link string
Date time.Time
Updated time.Time
Creator string
Hash itemHash
}
type v1Cache struct {
version byte
Ids map[feedDescriptor]feedId
NextId uint64
Feeds map[feedId]*cachedFeed
}
func (cache *v1Cache) Version() byte {
return cache.version
}
func New() Cache {
cache := v1Cache{
Ids: map[feedDescriptor]feedId{},
Feeds: map[feedId]*cachedFeed{},
NextId: startFeedId,
}
cache.version = currentVersion
return &cache
}
func cacheForVersion(version byte) (Cache, error) {
switch version {
case 1:
return New(), nil
default:
return nil, fmt.Errorf("unknown cache version '%d'", version)
}
}
func (cache *v1Cache) transformToCurrent() (Cache, error) {
return cache, nil
}
func (cache *v1Cache) getItem(id feedId) CachedFeed {
feed, ok := cache.Feeds[id]
if !ok {
feed = &cachedFeed{}
cache.Feeds[id] = feed
}
return feed
}
func (cache *v1Cache) findItem(feed *Feed) CachedFeed {
if feed.cached != nil {
return feed.cached.(*cachedFeed)
}
fId := feedDescriptor{Name: feed.Name, Url: feed.Url}
id, ok := cache.Ids[fId]
if !ok {
var otherId feedDescriptor
changed := false
for otherId, id = range cache.Ids {
if otherId.Name == fId.Name {
log.Warnf("Feed %s seems to have changed URLs: New '%s', old '%s'. Updating.",
fId.Name, fId.Url, otherId.Url)
changed = true
break
} else if otherId.Url == fId.Url {
log.Warnf("Feed with URL '%s' seems to have changed its name: New '%s', old '%s'. Updating",
fId.Url, fId.Name, otherId.Name)
changed = true
break
}
}
if changed {
delete(cache.Ids, otherId)
} else {
id = feedId(cache.NextId)
cache.NextId++
}
cache.Ids[fId] = id
}
item := cache.getItem(id)
feed.cached = item
return item
}
func (feeds *Feeds) StoreCache(fileName string) error {
cache := feeds.cache
if cache == nil {
return fmt.Errorf("trying to store nil cache")
}
if cache.Version() != currentVersion {
return fmt.Errorf("trying to store cache with unsupported version '%d' (current: '%d')", cache.Version(), currentVersion)
}
f, err := os.Create(fileName)
if err != nil {
return fmt.Errorf("trying to store cache to '%s': %w", fileName, err)
}
defer f.Close()
writer := bufio.NewWriter(f)
if err = writer.WriteByte(currentVersion); err != nil {
return fmt.Errorf("writing to '%s': %w", fileName, err)
}
encoder := gob.NewEncoder(writer)
if err = encoder.Encode(cache); err != nil {
return fmt.Errorf("encoding cache: %w", err)
}
writer.Flush()
log.Printf("Stored cache to '%s'.", fileName)
return nil
}
func (feeds *Feeds) LoadCache(fileName string) error {
cache, err := loadCache(fileName)
if err != nil {
return err
}
feeds.cache = cache
for _, feed := range feeds.feeds {
feed.cached = cache.findItem(feed)
}
return nil
}
func loadCache(fileName string) (Cache, error) {
f, err := os.Open(fileName)
if err != nil {
if errors.Is(err, os.ErrNotExist) {
// no cache there yet -- make new
return New(), nil
}
return nil, fmt.Errorf("opening cache at '%s': %w", fileName, err)
}
defer f.Close()
log.Printf("Loading cache from '%s'", fileName)
reader := bufio.NewReader(f)
version, err := reader.ReadByte()
if err != nil {
return nil, fmt.Errorf("reading from '%s': %w", fileName, err)
}
cache, err := cacheForVersion(version)
if err != nil {
return nil, err
}
decoder := gob.NewDecoder(reader)
if err = decoder.Decode(cache); err != nil {
return nil, fmt.Errorf("decoding for version '%d' from '%s': %w", version, fileName, err)
}
if cache, err = cache.transformToCurrent(); err != nil {
return nil, fmt.Errorf("cannot transform from version %d to %d: %w", version, currentVersion, err)
}
log.Printf("Loaded cache (version %d), transformed to version %d.", version, currentVersion)
return cache, nil
}
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