metricstarttimeprocessor: add reset detection for histograms (open-telemetry#38583)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
When an individual bucket counter decreases but the total count and sum
goes up, the adjuster now recognizes it as a reset.

<!-- Issue number (e.g. open-telemetry#1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes
open-telemetry#38582

<!--Describe what testing was performed and which tests were added.-->
#### Testing
Added unit tests.

<!--Describe the documentation added.-->
#### Documentation
N/A

<!--Please delete paragraphs that you did not use before submitting.-->

---------

Signed-off-by: Ridwan Sharif <[email protected]>
Co-authored-by: Antoine Toulme <[email protected]>

Author: ridwanmsharif

.chloggen/detect-resets.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: metricstarttimeprocessor
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Add reset detection for histograms
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [38582]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: []

processor/metricstarttimeprocessor/internal/datapointstorage/timeseries_map.go

@@ -101,6 +101,96 @@ func (tsm *TimeseriesMap) GC() {
 	tsm.Mark = false
 }
 
+// IsResetHistogram compares the given histogram datapoint h, to tsi.Histogram
+// and determines whether the metric has been reset based on the values.  It is
+// a reset if any of the bucket boundaries have changed, if any of the bucket
+// counts have decreased or if the total sum or count have decreased.
+func (tsi *TimeseriesInfo) IsResetHistogram(h pmetric.HistogramDataPoint) bool {
+	if h.Count() < tsi.Histogram.Count() {
+		return true
+	}
+	if h.Sum() < tsi.Histogram.Sum() {
+		return true
+	}
+
+	// Guard against bucket boundaries changes.
+	refBounds := tsi.Histogram.ExplicitBounds().AsRaw()
+	hBounds := h.ExplicitBounds().AsRaw()
+	if len(refBounds) != len(hBounds) {
+		return true
+	}
+	for i := range len(refBounds) {
+		if hBounds[i] != refBounds[i] {
+			return true
+		}
+	}
+
+	// We need to check individual buckets to make sure the counts are all increasing.
+	if tsi.Histogram.BucketCounts().Len() != h.BucketCounts().Len() {
+		return true
+	}
+	for i := range tsi.Histogram.BucketCounts().Len() {
+		if h.BucketCounts().At(i) < tsi.Histogram.BucketCounts().At(i) {
+			return true
+		}
+	}
+	return false
+}
+
+// IsResetExponentialHistogram compares the given exponential histogram
+// datapoint eh, to tsi.ExponentialHistogram and determines whether the metric
+// has been reset based on the values.  It is a reset if any of the bucket
+// boundaries have changed, if any of the bucket counts have decreased or if the
+// total sum or count have decreased.
+func (tsi *TimeseriesInfo) IsResetExponentialHistogram(eh pmetric.ExponentialHistogramDataPoint) bool {
+	// Same as the histogram implementation
+	if eh.Count() < tsi.ExponentialHistogram.Count() {
+		return true
+	}
+	if eh.Sum() < tsi.ExponentialHistogram.Sum() {
+		return true
+	}
+
+	// Guard against bucket boundaries changes.
+	if tsi.ExponentialHistogram.Scale() != eh.Scale() {
+		return true
+	}
+
+	// We need to check individual buckets to make sure the counts are all increasing.
+	if tsi.ExponentialHistogram.Positive().BucketCounts().Len() != eh.Positive().BucketCounts().Len() {
+		return true
+	}
+	for i := range tsi.ExponentialHistogram.Positive().BucketCounts().Len() {
+		if eh.Positive().BucketCounts().At(i) < tsi.ExponentialHistogram.Positive().BucketCounts().At(i) {
+			return true
+		}
+	}
+	if tsi.ExponentialHistogram.Negative().BucketCounts().Len() != eh.Negative().BucketCounts().Len() {
+		return true
+	}
+	for i := range tsi.ExponentialHistogram.Negative().BucketCounts().Len() {
+		if eh.Negative().BucketCounts().At(i) < tsi.ExponentialHistogram.Negative().BucketCounts().At(i) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// IsResetSummary compares the given summary datapoint s to tsi.Summary and
+// determines whether the metric has been reset based on the values.  It is a
+// reset if the count or sum has decreased.
+func (tsi *TimeseriesInfo) IsResetSummary(s pmetric.SummaryDataPoint) bool {
+	return s.Count() < tsi.Summary.Count() || s.Sum() < tsi.Summary.Sum()
+}
+
+// IsResetSum compares the given number datapoint s to tsi.Number and determines
+// whether the metric has been reset based on the values.  It is a reset if the
+// value has decreased.
+func (tsi *TimeseriesInfo) IsResetSum(s pmetric.NumberDataPoint) bool {
+	return s.DoubleValue() < tsi.Number.DoubleValue()
+}
+
 func newTimeseriesMap() *TimeseriesMap {
 	return &TimeseriesMap{Mark: true, TsiMap: map[TimeseriesKey]*TimeseriesInfo{}}
 }