budgeteer/server/budgeting.go

package server

import (
	"fmt"
	"net/http"
	"strconv"
	"time"

	"git.javil.eu/jacob1123/budgeteer/postgres"
	"git.javil.eu/jacob1123/budgeteer/postgres/numeric"
	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
)

func getFirstOfMonth(year, month int, location *time.Location) time.Time {
	return time.Date(year, time.Month(month), 1, 0, 0, 0, 0, location)
}

func getFirstOfMonthTime(date time.Time) time.Time {
	var monthM time.Month
	year, monthM, _ := date.Date()
	month := int(monthM)
	return getFirstOfMonth(year, month, date.Location())
}

type CategoryWithBalance struct {
	*postgres.GetCategoriesRow
	Available          numeric.Numeric
	AvailableLastMonth numeric.Numeric
	Activity           numeric.Numeric
	Assigned           numeric.Numeric
}

func NewCategoryWithBalance(category *postgres.GetCategoriesRow) CategoryWithBalance {
	return CategoryWithBalance{
		GetCategoriesRow:   category,
		Available:          numeric.Zero(),
		AvailableLastMonth: numeric.Zero(),
		Activity:           numeric.Zero(),
		Assigned:           numeric.Zero(),
	}
}

func getDate(c *gin.Context) (time.Time, error) {
	var year, month int
	yearString := c.Param("year")
	monthString := c.Param("month")
	if yearString == "" && monthString == "" {
		return getFirstOfMonthTime(time.Now()), nil
	}

	year, err := strconv.Atoi(yearString)
	if err != nil {
		return time.Time{}, fmt.Errorf("parse year: %w", err)
	}

	month, err = strconv.Atoi(monthString)
	if err != nil {
		return time.Time{}, fmt.Errorf("parse month: %w", err)
	}

	return getFirstOfMonth(year, month, time.Now().Location()), nil
}

func (h *Handler) budgetingForMonth(c *gin.Context) {
	budgetID := c.Param("budgetid")
	budgetUUID, err := uuid.Parse(budgetID)
	if err != nil {
		c.AbortWithStatusJSON(http.StatusBadRequest, ErrorResponse{"budgetid missing from URL"})
		return
	}

	budget, err := h.Service.GetBudget(c.Request.Context(), budgetUUID)
	if err != nil {
		c.AbortWithError(http.StatusBadRequest, err)
		return
	}

	firstOfMonth, err := getDate(c)
	if err != nil {
		c.Redirect(http.StatusTemporaryRedirect, "/budget/"+budgetUUID.String())
		return
	}

	categories, err := h.Service.GetCategories(c.Request.Context(), budgetUUID)
	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	firstOfNextMonth := firstOfMonth.AddDate(0, 1, 0)
	cumultativeBalances, err := h.Service.GetCumultativeBalances(c.Request.Context(), budgetUUID)
	if err != nil {
		c.AbortWithStatusJSON(http.StatusInternalServerError, ErrorResponse{fmt.Sprintf("error loading balances: %s", err)})
		return
	}

	categoriesWithBalance, moneyUsed := h.calculateBalances(
		budget, firstOfNextMonth, firstOfMonth, categories, cumultativeBalances)

	availableBalance := h.getAvailableBalance(categories, budget, moneyUsed, cumultativeBalances, firstOfNextMonth)

	data := struct {
		Categories       []CategoryWithBalance
		AvailableBalance numeric.Numeric
	}{categoriesWithBalance, availableBalance}
	c.JSON(http.StatusOK, data)
}

func (*Handler) getAvailableBalance(categories []postgres.GetCategoriesRow, budget postgres.Budget,
	moneyUsed numeric.Numeric, cumultativeBalances []postgres.GetCumultativeBalancesRow,
	firstOfNextMonth time.Time) numeric.Numeric {
	availableBalance := numeric.Zero()
	for _, cat := range categories {
		if cat.ID != budget.IncomeCategoryID {
			continue
		}
		availableBalance = moneyUsed

		for _, bal := range cumultativeBalances {
			if bal.CategoryID != cat.ID {
				continue
			}

			if !bal.Date.Before(firstOfNextMonth) {
				continue
			}

			availableBalance = availableBalance.Add(bal.Transactions)
		}
	}
	return availableBalance
}

func (h *Handler) budgeting(c *gin.Context) {
	budgetID := c.Param("budgetid")
	budgetUUID, err := uuid.Parse(budgetID)
	if err != nil {
		c.AbortWithStatusJSON(http.StatusBadRequest, ErrorResponse{"budgetid missing from URL"})
		return
	}

	budget, err := h.Service.GetBudget(c.Request.Context(), budgetUUID)
	if err != nil {
		c.AbortWithError(http.StatusNotFound, err)
		return
	}

	accounts, err := h.Service.GetAccountsWithBalance(c.Request.Context(), budgetUUID)
	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}

	data := struct {
		Accounts []postgres.GetAccountsWithBalanceRow
		Budget   postgres.Budget
	}{accounts, budget}

	c.JSON(http.StatusOK, data)
}

func (h *Handler) calculateBalances(budget postgres.Budget,
	firstOfNextMonth time.Time, firstOfMonth time.Time, categories []postgres.GetCategoriesRow,
	cumultativeBalances []postgres.GetCumultativeBalancesRow) ([]CategoryWithBalance, numeric.Numeric) {
	categoriesWithBalance := []CategoryWithBalance{}

	moneyUsed := numeric.Zero()
	for i := range categories {
		cat := &categories[i]
		// do not show hidden categories
		categoryWithBalance := h.CalculateCategoryBalances(cat, cumultativeBalances,
			firstOfNextMonth, &moneyUsed, firstOfMonth, budget)

		if cat.ID == budget.IncomeCategoryID {
			continue
		}

		categoriesWithBalance = append(categoriesWithBalance, categoryWithBalance)
	}

	return categoriesWithBalance, moneyUsed
}

func (*Handler) CalculateCategoryBalances(cat *postgres.GetCategoriesRow,
	cumultativeBalances []postgres.GetCumultativeBalancesRow, firstOfNextMonth time.Time,
	moneyUsed *numeric.Numeric, firstOfMonth time.Time, budget postgres.Budget) CategoryWithBalance {
	categoryWithBalance := NewCategoryWithBalance(cat)
	for _, bal := range cumultativeBalances {
		if bal.CategoryID != cat.ID {
			continue
		}

		// skip everything in the future
		if !bal.Date.Before(firstOfNextMonth) {
			continue
		}

		*moneyUsed = moneyUsed.Sub(bal.Assignments)
		categoryWithBalance.Available = categoryWithBalance.Available.Add(bal.Assignments)
		categoryWithBalance.Available = categoryWithBalance.Available.Add(bal.Transactions)
		if !categoryWithBalance.Available.IsPositive() && bal.Date.Before(firstOfMonth) {
			*moneyUsed = moneyUsed.Add(categoryWithBalance.Available)
			categoryWithBalance.Available = numeric.Zero()
		}

		if bal.Date.Before(firstOfMonth) {
			categoryWithBalance.AvailableLastMonth = categoryWithBalance.Available
		} else if bal.Date.Before(firstOfNextMonth) {
			categoryWithBalance.Activity = bal.Transactions
			categoryWithBalance.Assigned = bal.Assignments
		}
	}

	return categoryWithBalance
}