1 files changed, 196 insertions, 0 deletions
diff --git a/backend/internal/core/goal_service.go b/backend/internal/core/goal_service.go
new file mode 100644
index 0000000..60cffd5
--- /dev/null
+++ b/backend/internal/core/goal_service.go
@@ -0,0 +1,196 @@
+package core
+
+import (
+	"finance/backend/internal/database"
+	"finance/backend/internal/models"
+	"fmt"
+	"log"
+	"time"
+
+	"gorm.io/gorm"
+)
+
+// GoalService handles business logic for financial goals
+type GoalService struct {
+	db *gorm.DB
+}
+
+// NewGoalService creates and returns a new GoalService
+func NewGoalService() *GoalService {
+	return &GoalService{
+		db: database.DB,
+	}
+}
+
+// GoalProgress represents calculated progress data for a goal
+type GoalProgress struct {
+	Goal             models.Goal `json:"goal"`
+	PercentComplete  float64     `json:"percentComplete"`
+	AmountRemaining  int64       `json:"amountRemaining"`
+	DaysRemaining    int         `json:"daysRemaining,omitempty"`
+	RequiredPerDay   int64       `json:"requiredPerDay,omitempty"`
+	RequiredPerMonth int64       `json:"requiredPerMonth,omitempty"`
+	OnTrack          bool        `json:"onTrack"`
+}
+
+// GetGoalProgress retrieves a single goal with enhanced progress tracking data
+func (s *GoalService) GetGoalProgress(userID uint, goalID uint) (*GoalProgress, error) {
+	var goal models.Goal
+	if err := s.db.Where("id = ? AND user_id = ?", goalID, userID).First(&goal).Error; err != nil {
+		return nil, err
+	}
+
+	// Calculate progress
+	return s.calculateGoalProgress(&goal)
+}
+
+// GetAllGoalsProgress retrieves all goals for a user with enhanced progress data
+func (s *GoalService) GetAllGoalsProgress(userID uint, status string) ([]*GoalProgress, error) {
+	var goals []models.Goal
+
+	query := s.db.Where("user_id = ?", userID)
+	if status != "" {
+		query = query.Where("status = ?", status)
+	}
+
+	if err := query.Find(&goals).Error; err != nil {
+		return nil, err
+	}
+
+	progress := make([]*GoalProgress, 0, len(goals))
+	for i := range goals {
+		goalProgress, err := s.calculateGoalProgress(&goals[i])
+		if err != nil {
+			log.Printf("Error calculating progress for goal %d: %v", goals[i].ID, err)
+			continue
+		}
+		progress = append(progress, goalProgress)
+	}
+
+	return progress, nil
+}
+
+// calculateGoalProgress computes additional progress metrics for a goal
+func (s *GoalService) calculateGoalProgress(goal *models.Goal) (*GoalProgress, error) {
+	progress := &GoalProgress{
+		Goal:            *goal,
+		AmountRemaining: goal.TargetAmount - goal.CurrentAmount,
+	}
+
+	// Calculate percentage complete (avoid division by zero)
+	if goal.TargetAmount > 0 {
+		progress.PercentComplete = float64(goal.CurrentAmount) / float64(goal.TargetAmount) * 100
+	}
+
+	// Calculate time-based metrics if a target date exists
+	if !goal.TargetDate.IsZero() {
+		now := time.Now()
+
+		// Only calculate days remaining if target date is in the future
+		if goal.TargetDate.After(now) {
+			daysRemaining := int(goal.TargetDate.Sub(now).Hours() / 24)
+			progress.DaysRemaining = daysRemaining
+
+			// Calculate required savings per day/month
+			if progress.AmountRemaining > 0 && daysRemaining > 0 {
+				progress.RequiredPerDay = progress.AmountRemaining / int64(daysRemaining)
+				progress.RequiredPerMonth = progress.AmountRemaining / int64((daysRemaining+30-1)/30) // Ceiling division to months
+			}
+
+			// Calculate if on track based on time elapsed vs progress made
+			totalDuration := goal.TargetDate.Sub(goal.CreatedAt)
+			elapsedDuration := now.Sub(goal.CreatedAt)
+
+			if totalDuration > 0 {
+				expectedProgress := float64(elapsedDuration) / float64(totalDuration)
+				actualProgress := float64(goal.CurrentAmount) / float64(goal.TargetAmount)
+
+				// Consider on track if actual progress is at least 90% of expected progress
+				progress.OnTrack = actualProgress >= (expectedProgress * 0.9)
+			}
+		} else {
+			// Target date passed
+			progress.DaysRemaining = 0
+			progress.OnTrack = goal.CurrentAmount >= goal.TargetAmount
+		}
+	} else {
+		// No target date, so consider on track if any progress is made
+		progress.OnTrack = goal.CurrentAmount > 0
+	}
+
+	return progress, nil
+}
+
+// UpdateGoalFromTransactions updates goal progress based on recent transactions
+// This can be run periodically or when triggered by transaction changes
+func (s *GoalService) UpdateGoalFromTransactions(goalID uint) error {
+	var goal models.Goal
+	if err := s.db.First(&goal, goalID).Error; err != nil {
+		return err
+	}
+
+	// Get all related savings transactions for this goal
+	// This assumes a category field in transactions that indicates
+	// they are related to this goal (format: "Goal:<goalID>")
+	var transactions []models.Transaction
+	if err := s.db.Where("user_id = ? AND category = ?",
+		goal.UserID, fmt.Sprintf("Goal:%d", goalID)).Find(&transactions).Error; err != nil {
+		return err
+	}
+
+	// Calculate sum of all savings transactions
+	var totalSaved int64
+	for _, tx := range transactions {
+		if tx.Type == "Income" || tx.Type == "Savings" {
+			totalSaved += tx.Amount
+		} else if tx.Type == "Expense" {
+			totalSaved -= tx.Amount
+		}
+	}
+
+	// Update goal progress
+	goal.CurrentAmount = totalSaved
+
+	// Check if goal has been achieved
+	if goal.CurrentAmount >= goal.TargetAmount {
+		goal.Status = "Achieved"
+	}
+
+	return s.db.Save(&goal).Error
+}
+
+// LinkTransactionToGoal tags a transaction as contributing to a specific goal
+func (s *GoalService) LinkTransactionToGoal(txID uint, goalID uint) error {
+	var transaction models.Transaction
+	if err := s.db.First(&transaction, txID).Error; err != nil {
+		return err
+	}
+
+	// Set the category to indicate this transaction is for the goal
+	transaction.Category = fmt.Sprintf("Goal:%d", goalID)
+
+	// Save the updated transaction
+	if err := s.db.Save(&transaction).Error; err != nil {
+		return err
+	}
+
+	// Update the goal progress based on this and other transactions
+	return s.UpdateGoalFromTransactions(goalID)
+}
+
+// RecalculateAllGoals updates the progress of all active goals
+// This could be run daily as a background task
+func (s *GoalService) RecalculateAllGoals() error {
+	var goals []models.Goal
+	if err := s.db.Where("status = ?", "Active").Find(&goals).Error; err != nil {
+		return err
+	}
+
+	for _, goal := range goals {
+		if err := s.UpdateGoalFromTransactions(goal.ID); err != nil {
+			log.Printf("Error updating goal %d: %v", goal.ID, err)
+		}
+	}
+
+	return nil
+}