// Interpolate takes a counter value sampled at variable intervals and aligns each value with a <duration> ms boundary.
// The initial value is not output unless it appears exactly on a ms boundary.
// Runs of two or more missing values will be filled by NaN
func Interpolate(duration uint64, input *oproto.ValueStream) *oproto.ValueStream {
output := &oproto.ValueStream{}
var previousValue *oproto.Value
var timestamp uint64
for _, v := range input.Value {
if previousValue == nil {
if v.Timestamp%duration == 0 {
// Value is exactly on a timestamp
output.Value = append(output.Value, v)
previousValue = v
timestamp = v.Timestamp + duration
} else {
previousValue = v
previousValue.Timestamp = v.Timestamp / duration * duration
timestamp = previousValue.Timestamp + duration
}
continue
}
if v.Timestamp >= timestamp {
// Fill in any missing values before this one
rate := float64((v.DoubleValue - previousValue.DoubleValue))
for ; timestamp <= v.Timestamp; timestamp += duration {
pct := float64(timestamp-previousValue.Timestamp) / float64(v.Timestamp-previousValue.Timestamp)
newValue := previousValue.DoubleValue + (rate * pct)
output.Value = append(output.Value, &oproto.Value{
Timestamp: timestamp,
DoubleValue: newValue,
})
}
if previousValue.Timestamp < v.Timestamp {
if v.Timestamp%duration == 0 {
// Value is exactly on a timestamp
output.Value = append(output.Value, v)
previousValue = v
timestamp += duration
} else {
previousValue = v
}
}
}
}
return output
}
