remove unnecessary parameters

pom.xml

@@ -78,6 +78,12 @@
             <artifactId>spring-security-web</artifactId>
             <version>6.1.5</version>
         </dependency>
+        <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-math3 -->
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-math3</artifactId>
+            <version>3.6.1</version>
+        </dependency>
     </dependencies>
     <build>
         <defaultGoal>package</defaultGoal>

src/main/java/com/faf223/expensetrackerfaf/controller/ExpenseController.java

@@ -9,11 +9,9 @@ import com.faf223.expensetrackerfaf.model.User;
 import com.faf223.expensetrackerfaf.service.ExpenseCategoryService;
 import com.faf223.expensetrackerfaf.service.ExpenseService;
 import com.faf223.expensetrackerfaf.service.UserService;
+import com.faf223.expensetrackerfaf.util.DataExtender;
 import com.faf223.expensetrackerfaf.util.errors.ErrorResponse;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionDoesNotBelongToTheUserException;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionNotCreatedException;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionNotUpdatedException;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionsNotFoundException;
+import com.faf223.expensetrackerfaf.util.exceptions.*;
 import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.HttpStatus;
@@ -26,6 +24,7 @@ import org.springframework.transaction.annotation.Transactional;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.annotation.*;
 
+import java.math.BigDecimal;
 import java.time.LocalDate;
 import java.time.Month;
 import java.util.Collections;
@@ -134,6 +133,32 @@ public class ExpenseController {
         throw new TransactionsNotFoundException("The expenses have not been found");
     }
 
+    @GetMapping("/extend-data")
+    public ResponseEntity<List<BigDecimal>> extendData(@RequestParam Optional<String> extendValue,
+                                                       @RequestParam Optional<Integer> extrapolationCount) {
+        if(extendValue.isEmpty())
+            throw new RequiredParamMissingException("Extend value has not been specified");
+
+        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
+        User user;
+
+        if (authentication != null && authentication.getPrincipal() instanceof UserDetails userDetails)
+            user = userService.getUserByEmail(userDetails.getUsername());
+        else
+            user = null;
+
+        if(user == null)
+            throw new UserNotFoundException("User with the specified UUID has not been found");
+
+        if(extendValue.get().equalsIgnoreCase("i"))
+            return ResponseEntity.ok(DataExtender.interpolate(user.getExpenses()));
+
+        if(extendValue.get().equalsIgnoreCase("e"))
+            return extrapolationCount.map(integer -> ResponseEntity.ok(DataExtender.extrapolate(user.getExpenses(), integer))).orElseGet(() -> ResponseEntity.ok(DataExtender.extrapolate(user.getExpenses(), 10)));
+
+        throw new WrongParamValueException("Wrong extend value has been specified (use either \"i\" or \"e\")");
+    }
+
     @GetMapping("/categories")
     public ResponseEntity<List<ExpenseCategory>> getAllCategories() {
         List<ExpenseCategory> categories = expenseCategoryService.getAllCategories();

src/main/java/com/faf223/expensetrackerfaf/controller/GlobalExceptionHandler.java

@@ -12,72 +12,47 @@ public class GlobalExceptionHandler {
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleDoesNotBelongException(TransactionDoesNotBelongToTheUserException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
-
-        return new ResponseEntity<>(response, HttpStatus.FORBIDDEN);
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.FORBIDDEN);
     }
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleTransactionNotCreatedException(TransactionNotCreatedException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
-
-        return new ResponseEntity<>(response, HttpStatus.NOT_MODIFIED);
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.NOT_MODIFIED);
     }
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleTransactionsNotFoundException(TransactionsNotFoundException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
-
-        return new ResponseEntity<>(response, HttpStatus.NOT_FOUND);
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.NOT_FOUND);
     }
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleUserNotFoundException(UserNotFoundException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
-
-        return new ResponseEntity<>(response, HttpStatus.NOT_FOUND);
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.NOT_FOUND);
     }
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleTransactionNotUpdatedException(TransactionNotUpdatedException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
-
-        return new ResponseEntity<>(response, HttpStatus.NOT_MODIFIED);
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.NOT_MODIFIED);
     }
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleUserNotAuthenticatedException(UserNotAuthenticatedException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
-
-        return new ResponseEntity<>(response, HttpStatus.FORBIDDEN);
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.FORBIDDEN);
     }
 
     @ExceptionHandler
     private ResponseEntity<ErrorResponse> handleUserNotCreatedException(UserNotCreatedException e) {
-        ErrorResponse response = new ErrorResponse(
-                e.getMessage(),
-                System.currentTimeMillis()
-        );
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.NOT_MODIFIED);
+    }
 
-        return new ResponseEntity<>(response, HttpStatus.NOT_MODIFIED);
+    @ExceptionHandler
+    private ResponseEntity<ErrorResponse> handleRequiredParamMissingException(RequiredParamMissingException e) {
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.BAD_REQUEST);
+    }
+
+    @ExceptionHandler
+    private ResponseEntity<ErrorResponse> handleWrongParamValueException(WrongParamValueException e) {
+        return new ResponseEntity<>(new ErrorResponse(e.getMessage()), HttpStatus.BAD_REQUEST);
     }
 
 }

src/main/java/com/faf223/expensetrackerfaf/controller/IncomeController.java

@@ -9,11 +9,9 @@ import com.faf223.expensetrackerfaf.model.User;
 import com.faf223.expensetrackerfaf.service.IncomeCategoryService;
 import com.faf223.expensetrackerfaf.service.IncomeService;
 import com.faf223.expensetrackerfaf.service.UserService;
+import com.faf223.expensetrackerfaf.util.DataExtender;
 import com.faf223.expensetrackerfaf.util.errors.ErrorResponse;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionDoesNotBelongToTheUserException;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionNotCreatedException;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionNotUpdatedException;
-import com.faf223.expensetrackerfaf.util.exceptions.TransactionsNotFoundException;
+import com.faf223.expensetrackerfaf.util.exceptions.*;
 import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.HttpStatus;
@@ -26,6 +24,7 @@ import org.springframework.transaction.annotation.Transactional;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.annotation.*;
 
+import java.math.BigDecimal;
 import java.time.LocalDate;
 import java.time.Month;
 import java.util.Collections;
@@ -134,6 +133,32 @@ public class IncomeController {
         throw new TransactionsNotFoundException("The expenses have not been found");
     }
 
+    @GetMapping("/extend-data")
+    public ResponseEntity<List<BigDecimal>> extendData(@RequestParam Optional<String> extendValue,
+                                                       @RequestParam Optional<Integer> extrapolationCount) {
+        if(extendValue.isEmpty())
+            throw new RequiredParamMissingException("Extend value has not been specified");
+
+        Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
+        User user;
+
+        if (authentication != null && authentication.getPrincipal() instanceof UserDetails userDetails)
+            user = userService.getUserByEmail(userDetails.getUsername());
+        else
+            user = null;
+
+        if(user == null)
+            throw new UserNotFoundException("User with the specified UUID has not been found");
+
+        if(extendValue.get().equalsIgnoreCase("i"))
+            return ResponseEntity.ok(DataExtender.interpolate(user.getIncomes()));
+
+        if(extendValue.get().equalsIgnoreCase("e"))
+            return extrapolationCount.map(integer -> ResponseEntity.ok(DataExtender.extrapolate(user.getIncomes(), integer))).orElseGet(() -> ResponseEntity.ok(DataExtender.extrapolate(user.getIncomes(), 10)));
+
+        throw new WrongParamValueException("Wrong extend value has been specified (use either \"i\" or \"e\")");
+    }
+
     @GetMapping("/categories")
     public ResponseEntity<List<IncomeCategory>> getAllCategories() {
         List<IncomeCategory> categories = incomeCategoryService.getAllCategories();

src/main/java/com/faf223/expensetrackerfaf/util/DataExtender.java

@@ -0,0 +1,63 @@
+package com.faf223.expensetrackerfaf.util;
+
+import com.faf223.expensetrackerfaf.model.IMoneyTransaction;
+import org.apache.commons.math3.analysis.interpolation.LinearInterpolator;
+import org.apache.commons.math3.analysis.polynomials.PolynomialSplineFunction;
+
+import java.math.BigDecimal;
+import java.util.ArrayList;
+import java.util.List;
+
+public class DataExtender {
+
+    public static List<BigDecimal> interpolate(List<? extends IMoneyTransaction> transactions) {
+        List<BigDecimal> values = new ArrayList<>();
+
+        // Perform linear interpolation on the amount field
+        if (transactions.size() > 1) {
+            LinearInterpolator interpolator = new LinearInterpolator();
+
+            double[] xValues = new double[transactions.size()];
+            double[] yValues = new double[transactions.size()];
+
+            for (int i = 0; i < transactions.size(); i++) {
+                xValues[i] = i;
+                yValues[i] = transactions.get(i).getAmount().doubleValue();
+            }
+
+            PolynomialSplineFunction splineFunction = interpolator.interpolate(xValues, yValues);
+
+            // Interpolate values between the first and last data points
+            for (int i = 1; i < transactions.size() - 1; i++)
+                values.add(BigDecimal.valueOf(splineFunction.value(i + 0.5))); // Interpolate at the midpoint
+        }
+
+        return values;
+    }
+
+    public static List<BigDecimal> extrapolate(List<? extends IMoneyTransaction> transactions, int count) {
+        List<BigDecimal> values = new ArrayList<>();
+
+        // Perform linear extrapolation on the amount field
+        if (transactions.size() > 1) {
+            LinearInterpolator interpolator = new LinearInterpolator();
+
+            double[] xValues = new double[transactions.size()];
+            double[] yValues = new double[transactions.size()];
+
+            for (int i = 0; i < transactions.size(); i++) {
+                xValues[i] = i;
+                yValues[i] = transactions.get(i).getAmount().doubleValue();
+            }
+
+            PolynomialSplineFunction splineFunction = interpolator.interpolate(xValues, yValues);
+
+            // Extrapolate values beyond the last data point
+            for (int i = transactions.size(); i < transactions.size() + count; i++)
+                values.add(BigDecimal.valueOf(splineFunction.value(i))); // Extrapolate by extending the x-axis
+        }
+
+        return values;
+    }
+
+}

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/RequiredParamMissingException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class RequiredParamMissingException extends RuntimeException {
+    public RequiredParamMissingException(String message) {
+        super(message);
+    }
+}

src/main/java/com/faf223/expensetrackerfaf/util/exceptions/WrongParamValueException.java

@@ -0,0 +1,7 @@
+package com.faf223.expensetrackerfaf.util.exceptions;
+
+public class WrongParamValueException extends RuntimeException {
+    public WrongParamValueException(String message) {
+        super(message);
+    }
+}