82 lines
1.9 KiB
Go
82 lines
1.9 KiB
Go
package ledger
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import (
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"fmt"
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"maps"
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"math"
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"regexp"
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"time"
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)
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func RegisterWithCompoundingInterestPrediction(reg Register, window time.Duration, pattern string, apy float64) (Register, error) {
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lastBalances := make(Balances)
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p := regexp.MustCompile(pattern)
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for _, d := range reg.Dates() {
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if t, _ := dateToTime(d); time.Now().Before(t) {
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continue
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}
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for name := range reg[d] {
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if p.MatchString(name) {
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lastBalances[name] = reg[d][name]
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}
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}
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}
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predictedTimes := predictionTimes(window)
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result := maps.Clone(reg)
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for _, predictionTime := range predictedTimes {
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k := predictionTime.Format("2006-01")
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if _, ok := result[k]; !ok {
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result[k] = make(Balances)
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}
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for k2, v2 := range lastBalances {
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if _, ok := result[k][k2]; !ok {
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result[k][k2] = maps.Clone(v2)
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}
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}
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}
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addedSoFar := make(Balances)
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for _, predictionTime := range predictedTimes {
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k := predictionTime.Format("2006-01")
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for name := range lastBalances {
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if _, ok := addedSoFar[name]; !ok {
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addedSoFar[name] = make(Balance)
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}
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for currency := range result[k][name] {
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// A = P(1 + r/n)**nt
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p := result[k][name][currency] + addedSoFar[name][currency]
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r := apy
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n := 12.0
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t := 1.0 / 12.0
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result[k][name][currency] = p * math.Pow(1.0+(r/n), n*t)
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addedSoFar[name][currency] += (result[k][name][currency] - p)
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}
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}
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}
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return result, nil
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}
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func predictionTimes(window time.Duration) []time.Time {
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result := []time.Time{}
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last := time.Now()
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for last.Before(time.Now().Add(window)) {
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last = last.Add(-1 * time.Hour * 24 * time.Duration(last.Day())).Add(time.Hour * 24 * 33)
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result = append(result, last)
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}
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return result
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}
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func dateToTime(s string) (time.Time, error) {
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for _, layout := range []string{
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"2006-01-02",
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"2006-01",
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} {
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if t, err := time.ParseInLocation(layout, s, time.Local); err == nil {
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return t, err
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}
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}
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return time.Time{}, fmt.Errorf("no layout matching %q", s)
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}
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