// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package metricdata // import "go.opentelemetry.io/otel/sdk/metric/metricdata"

import (
	"encoding/json"
	"time"

	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/sdk/instrumentation"
	"go.opentelemetry.io/otel/sdk/resource"
)

// ResourceMetrics is a collection of ScopeMetrics and the associated Resource
// that created them.
type ResourceMetrics struct {
	// Resource represents the entity that collected the metrics.
	Resource *resource.Resource
	// ScopeMetrics are the collection of metrics with unique Scopes.
	ScopeMetrics []ScopeMetrics
}

// ScopeMetrics is a collection of Metrics Produces by a Meter.
type ScopeMetrics struct {
	// Scope is the Scope that the Meter was created with.
	Scope instrumentation.Scope
	// Metrics are a list of aggregations created by the Meter.
	Metrics []Metrics
}

// Metrics is a collection of one or more aggregated timeseries from an Instrument.
type Metrics struct {
	// Name is the name of the Instrument that created this data.
	Name string
	// Description is the description of the Instrument, which can be used in documentation.
	Description string
	// Unit is the unit in which the Instrument reports.
	Unit string
	// Data is the aggregated data from an Instrument.
	Data Aggregation
}

// Aggregation is the store of data reported by an Instrument.
// It will be one of: Gauge, Sum, Histogram.
type Aggregation interface {
	privateAggregation()
}

// Gauge represents a measurement of the current value of an instrument.
type Gauge[N int64 | float64] struct {
	// DataPoints are the individual aggregated measurements with unique
	// Attributes.
	DataPoints []DataPoint[N]
}

func (Gauge[N]) privateAggregation() {}

// Sum represents the sum of all measurements of values from an instrument.
type Sum[N int64 | float64] struct {
	// DataPoints are the individual aggregated measurements with unique
	// Attributes.
	DataPoints []DataPoint[N]
	// Temporality describes if the aggregation is reported as the change from the
	// last report time, or the cumulative changes since a fixed start time.
	Temporality Temporality
	// IsMonotonic represents if this aggregation only increases or decreases.
	IsMonotonic bool
}

func (Sum[N]) privateAggregation() {}

// DataPoint is a single data point in a timeseries.
type DataPoint[N int64 | float64] struct {
	// Attributes is the set of key value pairs that uniquely identify the
	// timeseries.
	Attributes attribute.Set
	// StartTime is when the timeseries was started. (optional)
	StartTime time.Time `json:",omitempty"`
	// Time is the time when the timeseries was recorded. (optional)
	Time time.Time `json:",omitempty"`
	// Value is the value of this data point.
	Value N

	// Exemplars is the sampled Exemplars collected during the timeseries.
	Exemplars []Exemplar[N] `json:",omitempty"`
}

// Histogram represents the histogram of all measurements of values from an instrument.
type Histogram[N int64 | float64] struct {
	// DataPoints are the individual aggregated measurements with unique
	// Attributes.
	DataPoints []HistogramDataPoint[N]
	// Temporality describes if the aggregation is reported as the change from the
	// last report time, or the cumulative changes since a fixed start time.
	Temporality Temporality
}

func (Histogram[N]) privateAggregation() {}

// HistogramDataPoint is a single histogram data point in a timeseries.
type HistogramDataPoint[N int64 | float64] struct {
	// Attributes is the set of key value pairs that uniquely identify the
	// timeseries.
	Attributes attribute.Set
	// StartTime is when the timeseries was started.
	StartTime time.Time
	// Time is the time when the timeseries was recorded.
	Time time.Time

	// Count is the number of updates this histogram has been calculated with.
	Count uint64
	// Bounds are the upper bounds of the buckets of the histogram. Because the
	// last boundary is +infinity this one is implied.
	Bounds []float64
	// BucketCounts is the count of each of the buckets.
	BucketCounts []uint64

	// Min is the minimum value recorded. (optional)
	Min Extrema[N]
	// Max is the maximum value recorded. (optional)
	Max Extrema[N]
	// Sum is the sum of the values recorded.
	Sum N

	// Exemplars is the sampled Exemplars collected during the timeseries.
	Exemplars []Exemplar[N] `json:",omitempty"`
}

// ExponentialHistogram represents the histogram of all measurements of values from an instrument.
type ExponentialHistogram[N int64 | float64] struct {
	// DataPoints are the individual aggregated measurements with unique
	// attributes.
	DataPoints []ExponentialHistogramDataPoint[N]
	// Temporality describes if the aggregation is reported as the change from the
	// last report time, or the cumulative changes since a fixed start time.
	Temporality Temporality
}

func (ExponentialHistogram[N]) privateAggregation() {}

// ExponentialHistogramDataPoint is a single exponential histogram data point in a timeseries.
type ExponentialHistogramDataPoint[N int64 | float64] struct {
	// Attributes is the set of key value pairs that uniquely identify the
	// timeseries.
	Attributes attribute.Set
	// StartTime is when the timeseries was started.
	StartTime time.Time
	// Time is the time when the timeseries was recorded.
	Time time.Time

	// Count is the number of updates this histogram has been calculated with.
	Count uint64
	// Min is the minimum value recorded. (optional)
	Min Extrema[N]
	// Max is the maximum value recorded. (optional)
	Max Extrema[N]
	// Sum is the sum of the values recorded.
	Sum N

	// Scale describes the resolution of the histogram. Boundaries are
	// located at powers of the base, where:
	//
	//   base = 2 ^ (2 ^ -Scale)
	Scale int32
	// ZeroCount is the number of values whose absolute value
	// is less than or equal to [ZeroThreshold].
	// When ZeroThreshold is 0, this is the number of values that
	// cannot be expressed using the standard exponential formula
	// as well as values that have been rounded to zero.
	// ZeroCount represents the special zero count bucket.
	ZeroCount uint64

	// PositiveBucket is range of positive value bucket counts.
	PositiveBucket ExponentialBucket
	// NegativeBucket is range of negative value bucket counts.
	NegativeBucket ExponentialBucket

	// ZeroThreshold is the width of the zero region. Where the zero region is
	// defined as the closed interval [-ZeroThreshold, ZeroThreshold].
	ZeroThreshold float64

	// Exemplars is the sampled Exemplars collected during the timeseries.
	Exemplars []Exemplar[N] `json:",omitempty"`
}

// ExponentialBucket are a set of bucket counts, encoded in a contiguous array
// of counts.
type ExponentialBucket struct {
	// Offset is the bucket index of the first entry in the Counts slice.
	Offset int32
	// Counts is an slice where Counts[i] carries the count of the bucket at
	// index (Offset+i). Counts[i] is the count of values greater than
	// base^(Offset+i) and less than or equal to base^(Offset+i+1).
	Counts []uint64
}

// Extrema is the minimum or maximum value of a dataset.
type Extrema[N int64 | float64] struct {
	value N
	valid bool
}

// MarshalText converts the Extrema value to text.
func (e Extrema[N]) MarshalText() ([]byte, error) {
	if !e.valid {
		return json.Marshal(nil)
	}
	return json.Marshal(e.value)
}

// MarshalJSON converts the Extrema value to JSON number.
func (e *Extrema[N]) MarshalJSON() ([]byte, error) {
	return e.MarshalText()
}

// NewExtrema returns an Extrema set to v.
func NewExtrema[N int64 | float64](v N) Extrema[N] {
	return Extrema[N]{value: v, valid: true}
}

// Value returns the Extrema value and true if the Extrema is defined.
// Otherwise, if the Extrema is its zero-value, defined will be false.
func (e Extrema[N]) Value() (v N, defined bool) {
	return e.value, e.valid
}

// Exemplar is a measurement sampled from a timeseries providing a typical
// example.
type Exemplar[N int64 | float64] struct {
	// FilteredAttributes are the attributes recorded with the measurement but
	// filtered out of the timeseries' aggregated data.
	FilteredAttributes []attribute.KeyValue
	// Time is the time when the measurement was recorded.
	Time time.Time
	// Value is the measured value.
	Value N
	// SpanID is the ID of the span that was active during the measurement. If
	// no span was active or the span was not sampled this will be empty.
	SpanID []byte `json:",omitempty"`
	// TraceID is the ID of the trace the active span belonged to during the
	// measurement. If no span was active or the span was not sampled this will
	// be empty.
	TraceID []byte `json:",omitempty"`
}

// Summary metric data are used to convey quantile summaries,
// a Prometheus (see: https://prometheus.io/docs/concepts/metric_types/#summary)
// data type.
//
// These data points cannot always be merged in a meaningful way. The Summary
// type is only used by bridges from other metrics libraries, and cannot be
// produced using OpenTelemetry instrumentation.
type Summary struct {
	// DataPoints are the individual aggregated measurements with unique
	// attributes.
	DataPoints []SummaryDataPoint
}

func (Summary) privateAggregation() {}

// SummaryDataPoint is a single data point in a timeseries that describes the
// time-varying values of a Summary metric.
type SummaryDataPoint struct {
	// Attributes is the set of key value pairs that uniquely identify the
	// timeseries.
	Attributes attribute.Set

	// StartTime is when the timeseries was started.
	StartTime time.Time
	// Time is the time when the timeseries was recorded.
	Time time.Time

	// Count is the number of updates this summary has been calculated with.
	Count uint64

	// Sum is the sum of the values recorded.
	Sum float64

	// (Optional) list of values at different quantiles of the distribution calculated
	// from the current snapshot. The quantiles must be strictly increasing.
	QuantileValues []QuantileValue
}

// QuantileValue is the value at a given quantile of a summary.
type QuantileValue struct {
	// Quantile is the quantile of this value.
	//
	// Must be in the interval [0.0, 1.0].
	Quantile float64

	// Value is the value at the given quantile of a summary.
	//
	// Quantile values must NOT be negative.
	Value float64
}