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package feed
import (
"bufio"
"encoding/gob"
"errors"
"fmt"
"os"
"time"
"github.com/Necoro/feed2imap-go/pkg/log"
)
type Version byte
const (
currentVersion Version = 1
)
type Cache interface {
findItem(*Feed) CachedFeed
Version() Version
Info() string
SpecificInfo(interface{}) string
transformToCurrent() (Cache, error)
}
type CachedFeed interface {
Checked(withFailure bool)
Failures() int
Last() time.Time
ID() string
filterItems(items []item, ignoreHash bool, alwaysNew bool) []item
Commit()
}
func cacheForVersion(version Version) (Cache, error) {
switch version {
case v1Version:
return newV1Cache(), nil
default:
return nil, fmt.Errorf("unknown cache version '%d'", version)
}
}
func storeCache(cache Cache, fileName string) error {
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(byte(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 newCache() (Cache, error) {
return cacheForVersion(currentVersion)
}
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 newCache()
}
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(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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