package indicator

import (
	"fmt"
	"time"

	"github.com/c9s/bbgo/pkg/types"
)

const MaxNumOfSMA = 5_000
const MaxNumOfSMATruncateSize = 100

var zeroTime time.Time

//go:generate callbackgen -type SMA
type SMA struct {
	types.SeriesBase
	types.IntervalWindow
	Values  types.Float64Slice
	Cache   *types.Queue
	EndTime time.Time

	UpdateCallbacks []func(value float64)
}

func (inc *SMA) Last() float64 {
	if inc.Values.Length() == 0 {
		return 0.0
	}
	return inc.Values.Last()
}

func (inc *SMA) Index(i int) float64 {
	if i >= inc.Values.Length() {
		return 0.0
	}

	return inc.Values.Index(i)
}

func (inc *SMA) Length() int {
	return inc.Values.Length()
}

var _ types.SeriesExtend = &SMA{}

func (inc *SMA) Update(value float64) {
	if inc.Cache == nil {
		inc.Cache = types.NewQueue(inc.Window)
		inc.SeriesBase.Series = inc
	}
	inc.Cache.Update(value)
	if inc.Cache.Length() < inc.Window {
		return
	}
	inc.Values.Push(types.Mean(inc.Cache))
	if inc.Values.Length() > MaxNumOfSMA {
		inc.Values = inc.Values[MaxNumOfSMATruncateSize-1:]
	}
}

func (inc *SMA) calculateAndUpdate(kLines []types.KLine) {
	var index = len(kLines) - 1
	var kline = kLines[index]
	if inc.EndTime != zeroTime && kline.EndTime.Before(inc.EndTime) {
		return
	}
	if inc.Cache == nil {
		for _, k := range kLines {
			inc.Update(KLineClosePriceMapper(k))
			inc.EndTime = k.EndTime.Time()
			inc.EmitUpdate(inc.Values.Last())
		}
	} else {
		inc.Update(KLineClosePriceMapper(kline))
		inc.EndTime = kline.EndTime.Time()
		inc.EmitUpdate(inc.Values.Last())
	}
}

func (inc *SMA) handleKLineWindowUpdate(interval types.Interval, window types.KLineWindow) {
	if inc.Interval != interval {
		return
	}

	inc.calculateAndUpdate(window)
}

func (inc *SMA) Bind(updater KLineWindowUpdater) {
	updater.OnKLineWindowUpdate(inc.handleKLineWindowUpdate)
}

func calculateSMA(kLines []types.KLine, window int, priceF KLinePriceMapper) (float64, error) {
	length := len(kLines)
	if length == 0 || length < window {
		return 0.0, fmt.Errorf("insufficient elements for calculating SMA with window = %d", window)
	}
	if length != window {
		return 0.0, fmt.Errorf("too much klines passed in, requires only %d klines", window)
	}

	sum := 0.0
	for _, k := range kLines {
		sum += priceF(k)
	}

	avg := sum / float64(window)
	return avg, nil
}