add delete-gauges flag to support re-sending a value when there was no u...

[markrechler]

This is adding a flag for a config option that statsd normally supports:
https://github.com/etsy/statsd/blob/master/docs/metric_types.md#gauges

[markrechler]

Did not notice there was an existing pull, #58. This has tests for the case where the flag is set to false as well.

[jehiah]

I guess the difference being we don't wan't "unchanged form last value" we want "any update or not" even if it's the same value.

[markrechler]

Updated.

[jehiah]

I think this is functional, but the length of these if statements is getting hard to parse. Any ideas for simplifying? Typically idiomatic Go moves longer if/else if/else if/else into a switch block to simplify.... (my attempt below)

currentValue := c
lastValue, hasLastValue := trackedGauges[g]
var hasChanged bool
if c != math.MaxUint64 {
    hasChanged = true
}
switch {
    case hasChanged:
        fmt.Fprintf(buffer, "%s %d %d\n", g, currentValue, now)
        trackedGauges[g] = c
        gauges[g] = math.MaxUint64
        num++
    case !hasChanged && hasLastValue &&  !*deleteGauges:
        fmt.Fprintf(buffer, "%s %d %d\n", g, lastValue, now)
        num++
    default:
        continue
}

[jehiah]

also i'm thinking that s/trackedGauges/lastGaugeValue might be a better variable name.

[markrechler]

Thanks for the tips, modified per comments.