budgeteer/server/budgeting.go

package server

import (
	"context"
	"fmt"
	"net/http"
	"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
	Activity  numeric.Numeric
	Assigned  numeric.Numeric
}

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

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/"+budget.ID.String())
		return
	}

	data, err := h.prepareBudgeting(c.Request.Context(), budget, firstOfMonth)
	if err != nil {
		c.AbortWithError(http.StatusInternalServerError, err)
		return
	}
	c.JSON(http.StatusOK, data)
}

func (h *Handler) prepareBudgeting(ctx context.Context, budget postgres.Budget, firstOfMonth time.Time) (BudgetingForMonthResponse, error) {
	firstOfNextMonth := firstOfMonth.AddDate(0, 1, 0)
	categories, err := h.Service.GetCategories(ctx, budget.ID)
	if err != nil {
		return BudgetingForMonthResponse{}, fmt.Errorf("error loading categories: %w", err)
	}

	cumultativeBalances, err := h.Service.GetCumultativeBalances(ctx, budget.ID)
	if err != nil {
		return BudgetingForMonthResponse{}, fmt.Errorf("error loading balances: %w", err)
	}

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

	data := BudgetingForMonthResponse{categoriesWithBalance, availableBalance}
	return data, nil
}

type BudgetingForMonthResponse struct {
	Categories       []CategoryWithBalance
	AvailableBalance numeric.Numeric
}

func (*Handler) getAvailableBalance(budget postgres.Budget,
	moneyUsed numeric.Numeric, cumultativeBalances []postgres.GetCumultativeBalancesRow,
	categoriesWithBalance []CategoryWithBalance, firstOfNextMonth time.Time,
) numeric.Numeric {
	availableBalance := moneyUsed

	for _, bal := range cumultativeBalances {
		if bal.CategoryID != budget.IncomeCategoryID {
			continue
		}

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

		availableBalance.AddI(bal.Transactions)
		availableBalance.AddI(bal.Assignments)
	}

	for i := range categoriesWithBalance {
		cat := &categoriesWithBalance[i]
		if cat.ID != budget.IncomeCategoryID {
			continue
		}

		cat.Available = availableBalance
	}
	return availableBalance
}

type BudgetingResponse struct {
	Accounts []postgres.GetAccountsWithBalanceRow
	Budget   postgres.Budget
}

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
	}

	h.returnBudgetingData(c, budgetUUID)
}

func (h *Handler) returnBudgetingData(c *gin.Context, budgetUUID uuid.UUID) {
	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 := BudgetingResponse{accounts, budget}

	c.JSON(http.StatusOK, data)
}

func (h *Handler) calculateBalances(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]
		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.SubI(bal.Assignments)
			categoryWithBalance.Available.AddI(bal.Assignments)
			categoryWithBalance.Available.AddI(bal.Transactions)
			if !categoryWithBalance.Available.IsPositive() && bal.Date.Before(firstOfMonth) {
				moneyUsed.AddI(categoryWithBalance.Available)
				categoryWithBalance.Available = numeric.Zero()
			}

			if bal.Date.Year() == firstOfMonth.Year() && bal.Date.Month() == firstOfMonth.Month() {
				categoryWithBalance.Activity = bal.Transactions
				categoryWithBalance.Assigned = bal.Assignments
			}
		}

		categoriesWithBalance = append(categoriesWithBalance, categoryWithBalance)
	}

	return categoriesWithBalance, moneyUsed
}