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mediatimeline/storage.go

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Go
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2019-04-23 13:54:42 +00:00
package main
import (
"encoding/gob"
"os"
"sort"
"sync"
"github.com/pkg/errors"
)
const tweetPageSize = 50
type store struct {
s []tweet
location string
lock sync.RWMutex
}
func init() {
gob.Register(tweet{})
}
func newStore(location string) (*store, error) {
s := &store{
s: []tweet{},
location: location,
}
return s, s.load()
}
func (s *store) StoreTweets(tweets []tweet) error {
s.lock.Lock()
defer s.lock.Unlock()
tmp := s.s
for _, t := range tweets {
var stored bool
for i := 0; i < len(tmp); i++ {
if tmp[i].ID == t.ID {
tmp[i] = t
stored = true
break
}
}
if !stored {
tmp = append(tmp, t)
}
}
sort.Slice(tmp, func(j, i int) bool { return tmp[i].ID < tmp[j].ID })
s.s = tmp
return s.save()
}
func (s *store) GetLastTweetID() uint64 {
s.lock.RLock()
defer s.lock.RUnlock()
if len(s.s) == 0 {
return 0
}
return s.s[0].ID
}
func (s *store) GetTweetPage(page int) ([]tweet, error) {
s.lock.RLock()
defer s.lock.RUnlock()
var (
start = (page - 1) * tweetPageSize
num = tweetPageSize
)
if start > len(s.s) {
return []tweet{}, nil
}
if start+num >= len(s.s) {
num = len(s.s) - start
}
return s.s[start:num], nil
}
func (s *store) GetTweetsSince(since uint64) ([]tweet, error) {
s.lock.RLock()
defer s.lock.RUnlock()
var i int
for i = 0; i < len(s.s); i++ {
if s.s[i].ID <= since {
break
}
}
return s.s[:i], nil
}
func (s *store) load() error {
s.lock.Lock()
defer s.lock.Unlock()
if _, err := os.Stat(s.location); err != nil {
if os.IsNotExist(err) {
// Leave a fresh store
return nil
}
return errors.Wrap(err, "Unable to stat storage file")
}
f, err := os.Open(s.location)
if err != nil {
return errors.Wrap(err, "Unable to open storage file")
}
defer f.Close()
tmp := []tweet{}
if err := gob.NewDecoder(f).Decode(&tmp); err != nil {
return errors.Wrap(err, "Unable to decode storage file")
}
s.s = tmp
return nil
}
func (s *store) save() error {
// No need to lock here, has write-lock from s.StoreTweets
f, err := os.Create(s.location)
if err != nil {
return errors.Wrap(err, "Unable to open store for writing")
}
defer f.Close()
return errors.Wrap(gob.NewEncoder(f).Encode(s.s), "Unable to encode store")
}