package timeseries

import (
	"math"
	"sort"
	"time"
)

func NewTimeSeriesData() *TimeSeriesData {
	return &TimeSeriesData{
		TS:   NewTimeSeries(),
		Meta: TimeSeriesMeta{},
	}
}

func (tsd TimeSeriesData) Len() int {
	return len(tsd.TS)
}

func (tsd *TimeSeriesData) Add(point TimePoint) *TimeSeriesData {
	if tsd.TS == nil {
		tsd.TS = NewTimeSeries()
	}

	tsd.TS = append(tsd.TS, point)
	return tsd
}

// Gets point timestamp rounded according to provided interval.
func (p *TimePoint) GetTimeFrame(interval time.Duration) time.Time {
	return p.Time.Truncate(interval)
}

// GroupBy groups points in given interval by applying provided `aggFunc`. Source time series should be sorted by time.
func (ts TimeSeries) GroupBy(interval time.Duration, aggFunc AggFunc) TimeSeries {
	if ts.Len() == 0 {
		return ts
	}

	groupedSeries := NewTimeSeries()
	frame := make([]TimePoint, 0)
	frameTS := ts[0].GetTimeFrame(interval)
	var pointFrameTs time.Time

	for _, point := range ts {
		pointFrameTs = point.GetTimeFrame(interval)

		// Iterate over points and push it into the frame if point time stamp fit the frame
		if pointFrameTs.Equal(frameTS) {
			frame = append(frame, point)
		} else if pointFrameTs.After(frameTS) {
			// If point outside frame, then we've done with current frame
			groupedSeries = append(groupedSeries, TimePoint{
				Time:  frameTS,
				Value: aggFunc(frame),
			})

			// Move frame window to next non-empty interval and fill empty by null
			frameTS = frameTS.Add(interval)
			for frameTS.Before(pointFrameTs) {
				groupedSeries = append(groupedSeries, TimePoint{
					Time:  frameTS,
					Value: nil,
				})
				frameTS = frameTS.Add(interval)
			}
			frame = []TimePoint{point}
		}
	}

	groupedSeries = append(groupedSeries, TimePoint{
		Time:  frameTS,
		Value: aggFunc(frame),
	})

	return groupedSeries
}

func (ts TimeSeries) GroupByRange(aggFunc AggFunc) TimeSeries {
	if ts.Len() == 0 {
		return ts
	}

	value := aggFunc(ts)
	return []TimePoint{
		{Time: ts[0].Time, Value: value},
		{Time: ts[ts.Len()-1].Time, Value: value},
	}
}

func (ts TimeSeries) Delta() TimeSeries {
	deltaSeries := NewTimeSeries()
	for i := 1; i < ts.Len(); i++ {
		currentPoint := ts[i]
		previousPoint := ts[i-1]
		if currentPoint.Value != nil && previousPoint.Value != nil {
			deltaValue := *currentPoint.Value - *previousPoint.Value
			deltaSeries = append(deltaSeries, TimePoint{Time: ts[i].Time, Value: &deltaValue})
		} else {
			deltaSeries = append(deltaSeries, TimePoint{Time: ts[i].Time, Value: nil})
		}
	}

	return deltaSeries
}

func (ts TimeSeries) Rate() TimeSeries {
	rateSeries := NewTimeSeries()
	var valueDelta float64 = 0
	for i := 1; i < ts.Len(); i++ {
		currentPoint := ts[i]
		previousPoint := ts[i-1]
		timeDelta := currentPoint.Time.Sub(previousPoint.Time)

		// Handle counter reset - use previous value
		if currentPoint.Value != nil && previousPoint.Value != nil && *currentPoint.Value >= *previousPoint.Value {
			valueDelta = (*currentPoint.Value - *previousPoint.Value) / timeDelta.Seconds()
		}

		value := valueDelta
		rateSeries = append(rateSeries, TimePoint{Time: ts[i].Time, Value: &value})
	}

	return rateSeries
}

func (ts TimeSeries) Transform(transformFunc TransformFunc) TimeSeries {
	for i, p := range ts {
		ts[i] = transformFunc(p)
	}
	return ts
}

func Filter(series []*TimeSeriesData, n int, order string, aggFunc AggFunc) []*TimeSeriesData {
	SortBy(series, "asc", aggFunc)

	maxN := int(math.Min(float64(n), float64(len(series))))
	filteredSeries := make([]*TimeSeriesData, maxN)
	for i := 0; i < maxN; i++ {
		switch order {
		case "top":
			filteredSeries[i] = series[len(series)-1-i]
		case "bottom":
			filteredSeries[i] = series[i]
		}
	}

	return filteredSeries
}

func AggregateBy(series []*TimeSeriesData, interval time.Duration, aggFunc AggFunc) *TimeSeriesData {
	aggregatedSeries := NewTimeSeries()

	// Combine all points into one time series
	for _, s := range series {
		aggregatedSeries = append(aggregatedSeries, s.TS...)
	}

	// GroupBy works correctly only with sorted time series
	aggregatedSeries.Sort()

	aggregatedSeries = aggregatedSeries.GroupBy(interval, aggFunc)
	aggregatedSeriesData := NewTimeSeriesData()
	aggregatedSeriesData.TS = aggregatedSeries
	return aggregatedSeriesData
}

func AggregateByRange(series []*TimeSeriesData, aggFunc AggFunc) *TimeSeriesData {
	aggregatedSeries := NewTimeSeries()

	// Combine all points into one time series
	for _, s := range series {
		aggregatedSeries = append(aggregatedSeries, s.TS...)
	}

	value := aggFunc(aggregatedSeries)
	aggregatedSeriesData := NewTimeSeriesData()
	if len(aggregatedSeries) > 0 {
		aggregatedSeriesData.TS = []TimePoint{
			{Time: aggregatedSeries[0].Time, Value: value},
			{Time: aggregatedSeries[aggregatedSeries.Len()-1].Time, Value: value},
		}
	}

	return aggregatedSeriesData
}

func (ts TimeSeries) Sort() {
	sorted := sort.SliceIsSorted(ts, ts.less())
	if !sorted {
		sort.Slice(ts, ts.less())
	}
}

// Implements less() function for sorting slice
func (ts TimeSeries) less() func(i, j int) bool {
	return func(i, j int) bool {
		return ts[i].Time.Before(ts[j].Time)
	}
}

func SumSeries(series []*TimeSeriesData) *TimeSeriesData {
	// Build unique set of time stamps from all series
	interpolatedTimeStampsMap := make(map[time.Time]time.Time)
	for _, s := range series {
		for _, p := range s.TS {
			interpolatedTimeStampsMap[p.Time] = p.Time
		}
	}

	// Convert to slice and sort
	interpolatedTimeStamps := make([]time.Time, 0)
	for _, ts := range interpolatedTimeStampsMap {
		interpolatedTimeStamps = append(interpolatedTimeStamps, ts)
	}
	sort.Slice(interpolatedTimeStamps, func(i, j int) bool {
		return interpolatedTimeStamps[i].Before(interpolatedTimeStamps[j])
	})

	interpolatedSeries := make([]TimeSeries, 0)

	for _, s := range series {
		if s.Len() == 0 {
			continue
		}

		pointsToInterpolate := make([]TimePoint, 0)

		currentPointIndex := 0
		for _, its := range interpolatedTimeStamps {
			currentPoint := s.TS[currentPointIndex]
			if its.Equal(currentPoint.Time) {
				if currentPointIndex < s.Len()-1 {
					currentPointIndex++
				}
			} else {
				pointsToInterpolate = append(pointsToInterpolate, TimePoint{Time: its, Value: nil})
			}
		}

		s.TS = append(s.TS, pointsToInterpolate...)
		s.TS.Sort()
		s.TS = interpolateSeries(s.TS)
		interpolatedSeries = append(interpolatedSeries, s.TS)
	}

	sumSeries := NewTimeSeriesData()
	for i := 0; i < len(interpolatedTimeStamps); i++ {
		var sum float64 = 0
		for _, s := range interpolatedSeries {
			if s[i].Value != nil {
				sum += *s[i].Value
			}
		}
		sumSeries.TS = append(sumSeries.TS, TimePoint{Time: interpolatedTimeStamps[i], Value: &sum})
	}

	return sumSeries
}

func interpolateSeries(series TimeSeries) TimeSeries {
	for i := series.Len() - 1; i >= 0; i-- {
		point := series[i]
		if point.Value == nil {
			left := findNearestLeft(series, i)
			right := findNearestRight(series, i)

			if left == nil && right == nil {
				continue
			}
			if left == nil {
				left = right
			}
			if right == nil {
				right = left
			}

			pointValue := linearInterpolation(point.Time, *left, *right)
			point.Value = &pointValue
			series[i] = point
		}
	}
	return series
}

func linearInterpolation(ts time.Time, left, right TimePoint) float64 {
	if left.Time.Equal(right.Time) {
		return (*left.Value + *right.Value) / 2
	} else {
		return *left.Value + (*right.Value-*left.Value)/float64((right.Time.UnixNano()-left.Time.UnixNano()))*float64((ts.UnixNano()-left.Time.UnixNano()))
	}
}

func findNearestRight(series TimeSeries, pointIndex int) *TimePoint {
	for i := pointIndex; i < series.Len(); i++ {
		if series[i].Value != nil {
			return &series[i]
		}
	}
	return nil
}

func findNearestLeft(series TimeSeries, pointIndex int) *TimePoint {
	for i := pointIndex; i > 0; i-- {
		if series[i].Value != nil {
			return &series[i]
		}
	}
	return nil
}