cashflow/main.go

package main

import (
	"fmt"
	"log"
	"math"
	"os"
	"os/exec"
	"regexp"
	"sort"
	"strconv"
	"strings"
	"time"

	"github.com/google/uuid"
	"github.com/sirupsen/logrus"

	"gopkg.in/yaml.v3"
)

const (
	maxWidth = 100
)

type timeSlice []time.Time

func (s timeSlice) Len() int           { return len(s) }
func (s timeSlice) Less(i, j int) bool { return s[i].Before(s[j]) }
func (s timeSlice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }

type transactionList []*Transaction

func (t transactionList) Len() int { return len(t) }
func (t transactionList) Less(i, j int) bool {
	if t[i].Date.Before(t[j].Date) {
		return true
	}

	if t[i].Amount < 0 && t[j].Amount < 0 {
		return math.Abs(t[i].Amount) > math.Abs(t[j].Amount)
	}

	return t[i].Amount > t[j].Amount
}
func (t transactionList) Swap(i, j int) { t[i], t[j] = t[j], t[i] }

type Account struct {
	Name    string  `yaml:"name"`
	Balance float64 `yaml:"balance"`
	Minimum float64 `yaml:"minimum"`
}

type Charge struct {
	Name   string
	Late   bool
	Amount float64
	Date   time.Time
}

type Config struct {
	Accounts     []Account
	Transactions transactionList
}

type ConfigYaml struct {
	Start        string
	End          string
	Accounts     []Account
	Credit       []TransactionYaml
	Transactions []TransactionYaml
}

type Transaction struct {
	Amount     float64
	Date       time.Time
	Delayable  bool
	Frequency  string
	ID         string
	Delayed    bool
	Name       string
	OriginDate time.Time
	Shift      string
}

type TransactionYaml struct {
	Name      string  `yaml:"name"`
	Amount    float64 `yaml:"amount"`
	Date      string  `yaml:"date"`
	Delayable string  `yaml:"delayable"`
	Frequency string  `yaml:"frequency,omitempty"`
	Shift     string  `yaml:"shift"`
}

type TransactionLog struct {
	StartDate    time.Time
	EndDate      time.Time
	Iteration    int
	LogDays      map[time.Time]*LogDay
	Transactions map[string]*Transaction
}

type LogDay struct {
	Date            time.Time
	StartingBalance []Account
	EndingBalance   []Account
	Transactions    map[string]*Transaction
}

func (tl *TransactionLog) dates() timeSlice {
	dateSlice := make(timeSlice, 0)
	for date := range tl.LogDays {
		dateSlice = append(dateSlice, date)
	}

	sort.Sort(dateSlice)

	return dateSlice
}

func (t *TransactionLog) first() time.Time {
	return t.dates()[0]
}

func (t *TransactionLog) last() time.Time {
	return t.dates()[t.dates().Len()-1]
}

func (logDay *LogDay) transactions() transactionList {
	transactions := transactionList{}

	for _, t := range logDay.Transactions {
		transactions = append(transactions, t)
	}

	sort.Sort(transactions)

	return transactions
}

func (tl *TransactionLog) nextLogDay(currentDate time.Time) *LogDay {
	var next time.Time
	for i, date := range tl.dates() {
		j := i + 1
		if j >= len(tl.dates()) {
			next = tl.dates()[i]
			break
		}
		if date == currentDate {
			next = tl.dates()[j]
			break
		}
	}

	return tl.LogDays[next]
}

func (tl *TransactionLog) previousLogDay(currentDate time.Time) *LogDay {
	var previous time.Time
	for _, date := range tl.dates() {
		if date == currentDate {
			break
		}
		previous = date
	}

	return tl.LogDays[previous]
}

func isWeekend(date time.Time) bool {
	if date.Weekday() == 0 || date.Weekday() == 6 {
		return true
	}

	return false
}

func parseDelayable(delayableString string) (bool, error) {
	if delayableString == "" {
		return true, nil
	}

	delayable, err := strconv.ParseBool(delayableString)
	if err != nil {
		return false, err
	}

	return delayable, nil
}

func parseTransaction(transactionYaml TransactionYaml) (*Transaction, error) {
	date, err := parseDate(transactionYaml.Date)
	if err != nil {
		return nil, err
	}

	date = stripTime(date)

	if transactionYaml.Shift == "" {
		transactionYaml.Shift = "late"
	}

	delayable, err := parseDelayable(transactionYaml.Delayable)
	if err != nil {
		return nil, err
	}

	transaction := &Transaction{
		Amount:     transactionYaml.Amount,
		Date:       stripTime(date),
		Delayable:  delayable,
		Frequency:  transactionYaml.Frequency,
		ID:         uuid.NewString(),
		Delayed:    false,
		Name:       transactionYaml.Name,
		OriginDate: date,
		Shift:      transactionYaml.Shift,
	}

	return transaction, nil
}

func parseConfig(configYaml ConfigYaml) *Config {
	config := &Config{
		Accounts:     configYaml.Accounts,
		Transactions: make([]*Transaction, 0),
	}

	for _, transaction := range configYaml.Credit {
		newTransaction, err := parseTransaction(transaction)
		if err != nil {
			logrus.Error(err)
		}
		config.Transactions = append(config.Transactions, newTransaction)
		logrus.Debugf("Parsed Transaction: %s", transaction.Name)
	}

	for _, transaction := range configYaml.Transactions {
		newTransaction, err := parseTransaction(transaction)
		if err != nil {
			logrus.Error(err)
		}
		config.Transactions = append(config.Transactions, newTransaction)
		logrus.Debugf("Parsed Transaction: %s", transaction.Name)
	}

	return config
}

func parseDate(dateString string) (time.Time, error) {
	currentDay := currentDay()

	regMatch, err := regexp.MatchString("^[0-9]{4}-[0-9]{1,2}-[0-9]{1,2}$", dateString)
	if err != nil {
		return time.Time{}, err
	}

	if regMatch {
		parsedDate, err := time.Parse("2006-1-2", dateString)
		if err != nil {
			return time.Time{}, err
		}
		return parsedDate, err
	}

	if dateString == "first" {
		if currentDay.Day() == 1 {
			return currentDay, nil
		} else {
			return firstOfMonth(currentDay).AddDate(0, 1, 0), nil
		}
	}

	if dateString == "last" {
		return lastOfMonth(currentDay), nil
	}

	dateString = fmt.Sprintf("%d-%d-%s", currentDay.Year(), currentDay.Month(), dateString)
	parsedDate, err := time.Parse("2006-1-2", dateString)
	if err != nil {
		return time.Time{}, err
	}

	if parsedDate.Before(currentDay) {
		return parsedDate.AddDate(0, 1, 0), nil
	}

	return parsedDate, nil
}

func ingestTransactions(transactions []*Transaction, transactionLog *TransactionLog) {
	for _, transaction := range transactions {
		if math.Abs(transaction.Amount) != 0 {
			transactionLog.addTransaction(transaction)
		}
	}
}

func (tl *TransactionLog) addTransaction(transaction *Transaction) {
	if transaction.Frequency == "" {
		tl.addDay(transaction.Date)
		tl.LogDays[transaction.Date].Transactions[transaction.ID] = transaction
		tl.Transactions[transaction.ID] = transaction

		logrus.Debugf("Adding transaction %s (%s | %f) to %s",
			transaction.ID, transaction.Name, transaction.Amount, transaction.Date.String())

		return
	}

	dateList := calculateFrequency(transaction.Frequency,
		transaction.Date, tl.EndDate, transaction.Delayable)

	for _, date := range dateList {
		tl.addDay(date)
		t := &Transaction{
			Amount:     transaction.Amount,
			Date:       date,
			Delayable:  transaction.Delayable,
			Frequency:  "",
			ID:         uuid.NewString(),
			Delayed:    false,
			Name:       transaction.Name,
			OriginDate: date,
			Shift:      transaction.Shift,
		}
		tl.LogDays[date].Transactions[t.ID] = t
		tl.Transactions[t.ID] = t

		logrus.Debugf("Adding transaction %s (%s | %f) to %s",
			t.ID, t.Name, t.Amount, t.Date.String())
	}
}

func (tl *TransactionLog) addDay(date time.Time) {
	if _, ok := tl.LogDays[date]; !ok {
		logrus.Debugf("Adding Log Day %s", stripTime(date).String())
		tl.LogDays[date] = &LogDay{
			Date:         stripTime(date),
			Transactions: make(map[string]*Transaction),
		}
	}
}

func (tl *TransactionLog) deleteDay(date time.Time) {
	if _, ok := tl.LogDays[date]; ok {
		logrus.Debugf("Deleting Log Day %s", date.String())
		delete(tl.LogDays, date)
	}
}

func calculateShift(transactionLog TransactionLog, transaction Transaction) time.Time {
	if isWeekend(transaction.Date) {
		add := 1
		newDate := transaction.Date
		if transaction.Shift == "early" {
			add = -1
		}

		for isWeekend(newDate) {
			newDate = newDate.AddDate(0, 0, add)
		}

		return newDate
	}

	if transaction.Shift == "early" {
		return transactionLog.previousLogDay(transaction.Date).Date
	}

	return transactionLog.nextLogDay(transaction.Date).Date
}

func (tl *TransactionLog) delayTransaction(transaction *Transaction) {
	newDate := calculateShift(*tl, *transaction)

	if newDate.Before(tl.first()) || newDate == transaction.Date {
		logrus.Debugf("Transaction not delayable %s (%s | %f)", transaction.ID, transaction.Name, transaction.Amount)
		transaction.Delayable = false
		return
	}

	if newDate.After(tl.last()) {
		newDate = tl.last()
	}

	if isWeekend(newDate) {
		newDate = newDate.AddDate(0, 0, 1)
	}

	tl.addDay(newDate)

	delete(tl.LogDays[transaction.Date].Transactions, transaction.ID)

	transaction.Date = newDate
	tl.LogDays[newDate].Transactions[transaction.ID] = transaction

	transaction.Delayed = true

}

func (tl *TransactionLog) executeTransaction(transaction *Transaction) bool {
	logDay := tl.LogDays[transaction.Date]
	accounts := make([]Account, len(logDay.EndingBalance))
	copy(accounts, logDay.EndingBalance)

	if isWeekend(transaction.Date) && transaction.Delayable {
		logrus.Debugf("Delaying %s due to weekend scheduling\n", transaction.Name)
		tl.delayTransaction(transaction)

		return false
	}

	logrus.Debugf("Balance: %f | Minimum: %f\n", accounts[0].Balance, accounts[0].Minimum)
	logrus.Debugf("Delayable: %t", transaction.Delayable)
	if !isAffordable(transaction.Amount, accounts[0].Balance, accounts[0].Minimum) && transaction.Delayable {
		logrus.Debugf("Delaying %s: %f (%s) due to lack of funds\n",
			transaction.Name, transaction.Amount, transaction.Date)
		tl.delayTransaction(transaction)

		return false
	}

	logrus.Debugf("Executing: %s (%s | %s | %f)",
		transaction.ID, logDay.Date.String(), transaction.Name, transaction.Amount)

	accounts[0].Balance = accounts[0].Balance + transaction.Amount

	logDay.EndingBalance = make([]Account, len(accounts))
	copy(logDay.EndingBalance, accounts)

	return true
}

func isAffordable(charge, balance, minimum float64) bool {
	if charge > 0 {
		return true
	}

	logrus.Debugf("Charge: %f | Balance - Miniumum: %f", charge, balance-minimum)
	logrus.Debugf("abs(charge) < (balance - minimum): %t", math.Abs(charge) < (balance-minimum))

	return math.Abs(charge) < (balance - minimum)
}

func currentDay() time.Time {
	return stripTime(time.Now())
}

func currentTZ() *time.Location {
	return time.Now().Local().Location()
}

func firstOfMonth(t time.Time) time.Time {
	return time.Date(t.Year(), t.Month(), 1, 0, 0, 0, 0, currentTZ())
}

func lastOfMonth(t time.Time) time.Time {
	return t.AddDate(0, 1, -t.Day())
}

func stripTime(t time.Time) time.Time {
	return time.Date(t.Year(), t.Month(), t.Day(), 0, 0, 0, 0, currentTZ())
}

func calculateFrequency(frequency string, startDate time.Time, endDate time.Time, hardDate bool) []time.Time {
	current := currentDay()
	initDate := startDate
	dateList := make([]time.Time, 0)

	for initDate.Before(endDate.AddDate(0, 0, 1)) {
		if !initDate.Before(current) || hardDate {
			dateList = append(dateList, initDate)
		}
		if frequency == "daily" {
			initDate = initDate.AddDate(0, 0, 1)
		} else if frequency == "weekly" {
			initDate = initDate.AddDate(0, 0, 7)
		} else if frequency == "biweekly" {
			initDate = initDate.AddDate(0, 0, 14)
		} else if frequency == "monthly" {
			if initDate == lastOfMonth(initDate) {
				initDate = lastOfMonth(firstOfMonth(initDate).AddDate(0, 1, 0))
			} else {
				initDate = initDate.AddDate(0, 1, 0)
			}
		} else {
			logrus.Fatal("Invalid Frequency")
		}
	}

	return dateList
}

func categorizeTransactions(transactions map[string]*Transaction) map[string][]string {
	var categorized = map[string][]string{
		"credits":  make([]string, 0),
		"late":     make([]string, 0),
		"standard": make([]string, 0),
	}

	for _, t := range transactions {
		if t.Amount > 0 {
			categorized["credits"] = append(categorized["credits"], t.ID)
		} else if t.Delayed {
			categorized["late"] = append(categorized["late"], t.ID)
		} else {
			categorized["standard"] = append(categorized["standard"], t.ID)
		}
	}

	return categorized
}

func (tl *TransactionLog) processTransactions(accounts []Account) bool {
	shifted := false
	endBalance := accounts

	logrus.Debugf("\n\nITERATION %d\n\n", tl.Iteration)
	for _, date := range tl.dates() {
		logrus.Debugf("Processing Log Day %s", date.String())
		logDay := tl.LogDays[date]
		logDay.StartingBalance = make([]Account, len(endBalance))
		logDay.EndingBalance = make([]Account, len(endBalance))
		copy(logDay.StartingBalance, endBalance)
		copy(logDay.EndingBalance, endBalance)
		categorized := categorizeTransactions(logDay.Transactions)
		if processTransactionsByID(tl, categorized["credits"]) {
			shifted = true
		}
		if processTransactionsByID(tl, categorized["late"]) {
			shifted = true
		}
		if processTransactionsByID(tl, categorized["standard"]) {
			shifted = true
		}
		logrus.Debugf("Starting Balance %s: %f", date, logDay.StartingBalance[0].Balance)
		logrus.Debugf("Ending Balance %s: %f", date, logDay.EndingBalance[0].Balance)
		endBalance = logDay.EndingBalance
		if shifted {
			break
		}
		if len(logDay.Transactions) == 0 {
			tl.deleteDay(date)
		}
	}

	tl.Iteration++
	return shifted
}

func processTransactionsByID(transactionLog *TransactionLog, transactionIDs []string) bool {
	shifted := false

	for _, id := range transactionIDs {
		transaction, ok := transactionLog.Transactions[id]
		if !ok {
			logrus.Fatalf("Transaction ID: %s not found in log\n", id)
		}
		logrus.Debugf("Processing %s (%s | %f)", id, transaction.Name, transaction.Amount)
		if !transactionLog.executeTransaction(transaction) {
			logrus.Debugf("Shifted due to: %s", transaction.Name)
			shifted = true
		}
	}

	return shifted
}

func getTerminalWidth() int {
	cmd := exec.Command("stty", "size")
	cmd.Stdin = os.Stdin
	out, err := cmd.Output()
	if err != nil {
		logrus.Fatal(err)
	}
	widthStr := string(out[:len(out)-1])
	sttyOut := strings.Split(widthStr, " ")
	width, err := strconv.Atoi(sttyOut[1])
	if err != nil {
		logrus.Fatal(err)
	}
	return width
}

func printWithMaxWidth(maxWidth int, suffix string, strs ...string) {
	total := 0
	whiteSpace := regexp.MustCompile(`^\s+$`)
	for _, str := range strs {
		line := ""
		if whiteSpace.MatchString(str) {
			fmt.Print(str)
			total += len(str)
			continue
		}
		words := strings.Fields(str)
		for _, word := range words {
			total += len(word)
			if len(line)+len(word)+1 >= maxWidth {
				fmt.Println(line)
				line = ""
			}
			if line == "" {
				line = word
			} else {
				line = line + " " + word
				total += 1
			}
		}
		fmt.Print(line)
	}

	repeatCount := maxWidth - total - len(suffix)
	if repeatCount < 0 {
		repeatCount = 0
	}

	terminate := strings.Repeat(" ", repeatCount) + suffix

	fmt.Println(terminate)

}

func printTransactionLine(amount float64, name, prefix, suffix string, maxWidth int) {
	segment := fmt.Sprintf("%s$%.2f", prefix, math.Abs(amount))
	spacer := strings.Repeat(" ", (maxWidth/4)-len(segment))
	printWithMaxWidth(maxWidth, suffix, segment, spacer, fmt.Sprintf("| %s", name))
}

func printOutput(logDay LogDay) {

	fullWidth := getTerminalWidth()

	if fullWidth > maxWidth {
		fullWidth = maxWidth
	}

	border := strings.Repeat("=", fullWidth)
	divider := strings.Repeat("-", fullWidth-1) + "|"

	fmt.Println(border)
	printWithMaxWidth(fullWidth, "|", logDay.Date.Format("Jan 02 2006"))

	for _, v := range logDay.StartingBalance {
		printTransactionLine(v.Balance, v.Name, "", "|", fullWidth)
	}
	for _, charge := range logDay.transactions() {
		prefix := "-"
		suffix := "|"
		if charge.Amount > 0 {
			prefix = "+"
		}

		if charge.Delayed {
			suffix = fmt.Sprintf("(%s - %s) |", "Late", charge.OriginDate.Format("Jan 02 2006"))
		} else if charge.Date != charge.OriginDate {
			suffix = fmt.Sprintf("(%s - %s) |", "Weekend", charge.OriginDate.Format("Jan 02 2006"))
		}

		printTransactionLine(charge.Amount, charge.Name, prefix, suffix, fullWidth)
	}

	fmt.Println(divider)
	for _, v := range logDay.EndingBalance {
		prefix := ""
		if v.Balance < 0 {
			prefix = "-"
		}
		printTransactionLine(v.Balance, v.Name, prefix, "|", fullWidth)
	}
	fmt.Printf("%s\n\n", border)
}

func main() {
	if len(os.Getenv("DEBUG")) > 0 {
		logrus.SetLevel(logrus.DebugLevel)
	}

	yfile, err := os.ReadFile(os.Args[1])
	if err != nil {
		log.Fatal(err)
	}

	var configYaml ConfigYaml

	err = yaml.Unmarshal(yfile, &configYaml)
	if err != nil {
		log.Fatal(err)
	}

	transactionLog := &TransactionLog{
		LogDays:      make(map[time.Time]*LogDay),
		Transactions: make(map[string]*Transaction),
	}

	if configYaml.Start != "" {
		transactionLog.StartDate, err = time.Parse("2006-1-2", configYaml.Start)
		if err != nil {
			logrus.Error(err)
		}
	}

	if configYaml.End != "" {
		transactionLog.EndDate, err = time.Parse("2006-1-2", configYaml.End)
		if err != nil {
			logrus.Error(err)
		}
	}

	config := parseConfig(configYaml)

	sort.Sort(config.Transactions)

	if transactionLog.StartDate == (time.Time{}) {
		transactionLog.StartDate = config.Transactions[0].Date
	}

	if transactionLog.EndDate == (time.Time{}) {
		transactionLog.EndDate = config.Transactions[len(config.Transactions)-1].Date
	}

	ingestTransactions(config.Transactions, transactionLog)

	shifted := true
	for shifted {
		shifted = false
		shifted = transactionLog.processTransactions(config.Accounts)
	}

	for _, date := range transactionLog.dates() {
		logDay := transactionLog.LogDays[date]
		printOutput(*logDay)
	}

}