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package imap
import (
"fmt"
"sync/atomic"
"time"
)
type UIDValidityGenerator interface {
Generate() (UID, error)
}
type EpochUIDValidityGenerator struct {
epochStart time.Time
lastUID uint32
}
func NewEpochUIDValidityGenerator(epochStart time.Time) *EpochUIDValidityGenerator {
return &EpochUIDValidityGenerator{
epochStart: epochStart,
}
}
func DefaultEpochUIDValidityGenerator() *EpochUIDValidityGenerator {
return NewEpochUIDValidityGenerator(time.Date(2023, 2, 1, 0, 0, 0, 0, time.UTC))
}
func (e *EpochUIDValidityGenerator) Generate() (UID, error) {
timeStamp := uint64(time.Now().Sub(e.epochStart).Seconds())
if timeStamp > uint64(0xFFFFFFFF) {
return 0, fmt.Errorf("failed to generate uid validity, interval exceeded maximum capacity")
}
timeStampU32 := uint32(timeStamp)
// This loops is here to ensure that two successive calls to Generate that happen during the same second
// can still generate unique values. To avoid waiting another second until the values are different,
// we keep bumping the last generated value until it is greater than the last generated value.
for {
lastGenerated := atomic.LoadUint32(&e.lastUID)
// Not enough time elapsed between the last time
if lastGenerated >= timeStampU32 {
if timeStampU32 == 0xFFFFFFFF {
return 0, fmt.Errorf("failed to generate uid validity, interval exceeded maximum capacity")
}
timeStampU32 += 1
continue
}
if !atomic.CompareAndSwapUint32(&e.lastUID, lastGenerated, timeStampU32) {
continue
}
return UID(timeStampU32), nil
}
}
type IncrementalUIDValidityGenerator struct {
counter uint32
}
func (i *IncrementalUIDValidityGenerator) Generate() (UID, error) {
return UID(atomic.AddUint32(&i.counter, 1)), nil
}
func (i *IncrementalUIDValidityGenerator) GetValue() UID {
return UID(atomic.LoadUint32(&i.counter))
}
func NewIncrementalUIDValidityGenerator() *IncrementalUIDValidityGenerator {
return &IncrementalUIDValidityGenerator{}
}
type FixedUIDValidityGenerator struct {
Value UID
}
func (f FixedUIDValidityGenerator) Generate() (UID, error) {
return f.Value, nil
}
func NewFixedUIDValidityGenerator(value UID) *FixedUIDValidityGenerator {
return &FixedUIDValidityGenerator{Value: value}
}
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