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package forms
import (
"encoding/json"
"io"
"os"
)
type Sequence struct {
f *os.File
err error
}
func OpenSequence(path string) Sequence {
f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0o644)
return Sequence{f, err}
}
func (s Sequence) Close() error {
if s.err != nil {
return s.err
}
return s.f.Close()
}
func (s Sequence) Load() (int64, error) {
if s.err != nil {
return 0, s.err
}
if _, err := s.f.Seek(0, io.SeekStart); err != nil {
return 0, err
}
var seq int64
if err := json.NewDecoder(s.f).Decode(&seq); err != nil {
if err != io.EOF {
return 0, err
}
}
return seq, nil
}
func (s Sequence) Set(seq int64) (int64, error) {
if s.err != nil {
return 0, s.err
}
if err := s.f.Truncate(0); err != nil {
return 0, err
}
if _, err := s.f.Seek(0, io.SeekStart); err != nil {
return 0, err
}
defer s.f.Sync()
return seq, json.NewEncoder(s.f).Encode(&seq)
}
func (s Sequence) Incr(increment int64) (int64, error) {
seq, err := s.Load()
if err != nil {
return 0, err
}
return s.Set(seq + increment)
}
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