carvalho-finances/apps/api/internal/service/cdi.go

package service

import (
	"context"
	"encoding/json"
	"fmt"
	"net/http"
	"time"

	"financeiro-carvalho/internal/model"
	"financeiro-carvalho/internal/repository"
)

const bcbCDIURL = "https://api.bcb.gov.br/dados/serie/bcdata.sgs.12/dados?formato=json&dataInicial=%s&dataFinal=%s"

type CDIYieldService struct {
	accountRepo repository.AccountRepoWithYield
	txRepo      repository.ManualTransactionRepository
	client      *http.Client
}

func NewCDIYieldService(accountRepo repository.AccountRepoWithYield, txRepo repository.ManualTransactionRepository) *CDIYieldService {
	return &CDIYieldService{
		accountRepo: accountRepo,
		txRepo:      txRepo,
		client:      &http.Client{Timeout: 10 * time.Second},
	}
}

// ApplyYield fetches CDI rates and creates a yield transaction for the account if applicable.
func (s *CDIYieldService) ApplyYield(ctx context.Context, a *model.Account) error {
	if a.YieldType != "cdi" {
		return nil
	}

	// Determine the start date (day after last yield)
	yesterday := time.Now().AddDate(0, 0, -1).Format("2006-01-02")
	startDate := a.CreatedAt[:10] // default: account creation date
	if a.LastYieldDate != nil && *a.LastYieldDate != "" {
		startDate = *a.LastYieldDate
		// start is exclusive: add one day
		t, err := time.Parse("2006-01-02", startDate)
		if err != nil {
			return nil
		}
		startDate = t.AddDate(0, 0, 1).Format("2006-01-02")
	}

	if startDate > yesterday {
		// nothing to calculate yet
		return nil
	}

	rates, err := s.fetchCDIRates(startDate, yesterday)
	if err != nil {
		// BCB API unreachable — skip silently; will retry next load
		return nil
	}
	if len(rates) == 0 {
		return nil
	}

	// Fill gaps (weekends/holidays) using last known rate
	rateMap := make(map[string]float64, len(rates))
	for _, r := range rates {
		rateMap[r.date] = r.value
	}

	compound := 1.0
	lastRate := rates[0].value
	start, _ := time.Parse("2006-01-02", startDate)
	end, _ := time.Parse("2006-01-02", yesterday)
	for d := start; !d.After(end); d = d.AddDate(0, 0, 1) {
		key := d.Format("2006-01-02")
		if r, ok := rateMap[key]; ok {
			lastRate = r
		}
		compound *= 1 + lastRate/100
	}

	cdiPct := a.CDIPercentage
	if cdiPct <= 0 {
		cdiPct = 100
	}
	yieldAmount := a.Balance * (compound - 1) * (cdiPct / 100)
	if yieldAmount <= 0 {
		return nil
	}

	period := fmt.Sprintf("%s → %s", startDate, yesterday)
	tx := model.Transaction{
		Date:        time.Now().Format("2006-01-02"),
		Amount:      yieldAmount,
		Description: fmt.Sprintf("Rendimento CDI — %s", period),
		Type:        "income",
		Source:      "yield",
		AccountID:   &a.ID,
	}
	if _, err := s.txRepo.Create(ctx, tx); err != nil {
		return err
	}

	return s.accountRepo.UpdateLastYieldDate(ctx, a.ID, yesterday)
}

type bcbEntry struct {
	date  string
	value float64
}

func (s *CDIYieldService) fetchCDIRates(startDate, endDate string) ([]bcbEntry, error) {
	// BCB API uses DD/MM/YYYY format
	start, _ := time.Parse("2006-01-02", startDate)
	end, _ := time.Parse("2006-01-02", endDate)
	url := fmt.Sprintf(bcbCDIURL, start.Format("02/01/2006"), end.Format("02/01/2006"))

	resp, err := s.client.Get(url)
	if err != nil {
		return nil, err
	}
	defer resp.Body.Close()

	var raw []struct {
		Data  string `json:"data"`
		Valor string `json:"valor"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&raw); err != nil {
		return nil, err
	}

	var out []bcbEntry
	for _, r := range raw {
		// BCB date format: DD/MM/YYYY → convert to YYYY-MM-DD
		t, err := time.Parse("02/01/2006", r.Data)
		if err != nil {
			continue
		}
		var v float64
		fmt.Sscanf(r.Valor, "%f", &v)
		out = append(out, bcbEntry{date: t.Format("2006-01-02"), value: v})
	}
	return out, nil
}