package ana

import (
	"maps"
	"slices"
	"sort"
	"time"

	"gogs.inhome.blapointe.com/ana-ledger/ledger"
)

func RegisterWithContributionPrediction(reg ledger.Register, window time.Duration) (ledger.Register, error) {
	result := make(ledger.Register)
	result.PushAll(reg)
	for _, name := range result.Names() {
		err := registerWithContributionPredictionForName(result, window, name)
		if err != nil {
			return nil, err
		}
	}
	return result, nil
}

func registerWithContributionPredictionForName(reg ledger.Register, window time.Duration, name string) error {
	latest := make(ledger.Balance)
	for _, d := range reg.Dates() {
		if _, ok := reg[d][name]; ok {
			latest = reg[d][name]
		}
	}
	for _, predictionTime := range predictionTimes(window) {
		k := predictionTime.Format("2006-01")
		if _, ok := reg[k]; !ok {
			reg[k] = make(ledger.Balances)
		}
		reg[k][name] = maps.Clone(latest)
	}
	for c := range latest {
		err := registerWithContributionPredictionForNameForCurrency(reg, window, name, c)
		if err != nil {
			return err
		}
	}
	return nil
}

func registerWithContributionPredictionForNameForCurrency(reg ledger.Register, window time.Duration, name string, currency ledger.Currency) error {
	type contribution struct {
		t time.Time
		v float64
	}
	contributions := make([]contribution, 0)
	for d := range reg {
		t, err := dateToTime(d)
		if err != nil {
			return err
		}
		if time.Since(t) > time.Hour*24*180 || time.Now().Before(t) { // only include -6months..now
			continue
		}
		if v, ok := reg[d][name][currency]; ok && (len(contributions) == 0 || contributions[len(contributions)-1].v != v) {
			contributions = append(contributions, contribution{t: t, v: v})
		}
	}
	sort.Slice(contributions, func(i, j int) bool {
		return contributions[i].t.Before(contributions[j].t)
	})
	if len(contributions) < 5 {
		return nil
	}

	getMedianValueDelta := func(contributions []contribution) float64 {
		values := make([]float64, len(contributions))
		for i := 1; i < len(contributions); i++ {
			values[i] = contributions[i].v - contributions[i-1].v
		}
		slices.Sort(values)
		return values[len(values)/2]
	}
	getMedianLapse := func(contributions []contribution) time.Duration {
		lapses := make([]time.Duration, len(contributions)-1)
		for i := 1; i < len(contributions); i++ {
			lapses = append(lapses, contributions[i].t.Sub(contributions[i-1].t))
		}
		slices.Sort(lapses)
		return lapses[len(lapses)/2]
	}
	contributionsSlice := func(percent float64) []contribution {
		wouldBe := int(percent * float64(len(contributions)))
		if wouldBe == 0 {
			wouldBe = 2
		}
		return contributions[len(contributions)-1-wouldBe:]
	}

	eighth := contributionsSlice(7.0 / 8.0)
	quarter := contributionsSlice(3.0 / 4.0)
	half := contributionsSlice(1.0 / 2.0)
	medianValueDelta := func() float64 {
		medians := []float64{
			getMedianValueDelta(eighth),
			getMedianValueDelta(quarter),
			getMedianValueDelta(half),
		}
		slices.Sort(medians)
		return medians[1]
	}()
	medianLapse := func() time.Duration {
		medians := []time.Duration{
			getMedianLapse(eighth),
			getMedianLapse(quarter),
			getMedianLapse(half),
		}
		slices.Sort(medians)
		return medians[1]
	}()

	for _, predictionTime := range predictionTimes(window) {
		k := predictionTime.Format("2006-01")
		expectedDelta := float64(predictionTime.Sub(time.Now())) * medianValueDelta / float64(medianLapse)
		reg[k][name][currency] += expectedDelta
	}
	return nil
}