budgeteer/server/budgeting.go

package server

import (
	"context"
	"fmt"
	"net/http"

	"git.javil.eu/jacob1123/budgeteer/postgres"
	"git.javil.eu/jacob1123/budgeteer/postgres/numeric"
	"github.com/google/uuid"
	"github.com/labstack/echo/v4"
)

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

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

func (h *Handler) budgetingForMonth(c echo.Context) error {
	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 {
		return echo.NewHTTPError(http.StatusBadRequest, err)
		return
	}

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

	data, err := h.getBudgetingViewForMonth(c.Request().Context(), budget, month)
	if err != nil {
		return echo.NewHTTPError(http.StatusInternalServerError, err)
		return
	}
	c.JSON(http.StatusOK, data)
}

func (h *Handler) getBudgetingViewForMonth(ctx context.Context, budget postgres.Budget, month Month) (BudgetingForMonthResponse, error) {
	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, overspentLastMonth := h.calculateBalances(budget, month, categories, cumultativeBalances)
	availableBalance := h.getAvailableBalance(budget, month, moneyUsed, cumultativeBalances)

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

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

func (*Handler) getAvailableBalance(budget postgres.Budget, month Month,
	moneyUsed numeric.Numeric, cumultativeBalances []postgres.GetCumultativeBalancesRow,
) numeric.Numeric {
	availableBalance := moneyUsed

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

		if month.InFuture(bal.Date) {
			continue
		}

		availableBalance.AddI(bal.Transactions)
		availableBalance.AddI(bal.Assignments) // should be zero, but who knows
	}

	return availableBalance
}

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

func (h *Handler) budget(c echo.Context) error {
	budgetID := c.Param("budgetid")
	budgetUUID, err := uuid.Parse(budgetID)
	if err != nil {
		return echo.NewHTTPError(http.StatusBadRequest, "budgetid missing from URL")
	}

	return h.getBudget(c, budgetUUID)
}

func (h *Handler) getBudget(c echo.Context, budgetUUID uuid.UUID) error {
	budget, err := h.Service.GetBudget(c.Request().Context(), budgetUUID)
	if err != nil {
		return echo.NewHTTPError(http.StatusNotFound, err)
	}

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

	data := BudgetingResponse{accounts, budget}

	return c.JSON(http.StatusOK, data)
}

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

	moneyUsed := numeric.Zero()
	overspentLastMonth := numeric.Zero()
	categories = append(categories, postgres.GetCategoriesRow{
		Group: "Income",
		Name:  "No Category",
		ID:    uuid.UUID{},
	})
	for i := range categories {
		cat := &categories[i]
		if cat.ID == budget.IncomeCategoryID {
			continue
		}

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

			// skip everything in the future
			if month.InFuture(bal.Date) {
				continue
			}

			moneyUsed.SubI(bal.Assignments)
			if month.InPresent(bal.Date) {
				categoryWithBalance.Activity = bal.Transactions
				categoryWithBalance.Assigned = bal.Assignments
				continue
			}

			categoryWithBalance.AvailableLastMonth.AddI(bal.Assignments)
			categoryWithBalance.AvailableLastMonth.AddI(bal.Transactions)
			if !categoryWithBalance.AvailableLastMonth.IsPositive() {
				moneyUsed.AddI(categoryWithBalance.AvailableLastMonth)
				if month.Previous().InPresent(bal.Date) {
					overspentLastMonth.AddI(categoryWithBalance.AvailableLastMonth)
				}
				categoryWithBalance.AvailableLastMonth = numeric.Zero()
			}
		}

		categoriesWithBalance = append(categoriesWithBalance, categoryWithBalance)
	}

	return categoriesWithBalance, moneyUsed, overspentLastMonth
}