public class MainActivity extends AppCompatActivity {
    private TextView monthText;
    private TextView yearText;
    private GridLayout calendarGrid;
    private LocalDate currentDisplayMonth;
    private LocalDate tappedSelectedDate;

    private final Map<TextView, LocalDate> cellDateMap = new HashMap<>();
    private TextView previouslySelectedCellView = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        currentDisplayMonth = LocalDate.now();
        setContentView(R.layout.activity_main);
        monthText = findViewById(R.id.monthText);
        yearText = findViewById(R.id.yearText);
        calendarGrid = findViewById(R.id.calendarGrid);
        Button prevMonthButton = findViewById(R.id.prevMonthButton);
        Button nextMonthButton = findViewById(R.id.nextMonthButton);
        if (monthText == null || yearText == null || calendarGrid == null || prevMonthButton == null || nextMonthButton == null) {
            Log.e("MainActivityLifecycle", "onCreate: One or more views are null!");
            return;
        }

        updateMonthYearDisplay();
        drawCalendar();

        prevMonthButton.setOnClickListener(v -> {
            if (currentDisplayMonth == null) {
                Log.e("MainActivityLogic", "prevMonthButton: currentDisplayMonth is null!");
                currentDisplayMonth = LocalDate.now();
            }
            currentDisplayMonth = currentDisplayMonth.minusMonths(1);
            clearSelection();
            updateMonthYearDisplay();
            drawCalendar();
        });

        ViewCompat.setOnApplyWindowInsetsListener(findViewById(R.id.main), (v, insets) -> {
            Insets systemBars = insets.getInsets(WindowInsetsCompat.Type.systemBars());
            v.setPadding(systemBars.left, systemBars.top, systemBars.right, systemBars.bottom);
            return insets;
        });
    }

    private void updateMonthYearDisplay() {
        if (monthText != null && yearText != null && currentDisplayMonth != null) {
            DateTimeFormatter monthFormatter = DateTimeFormatter.ofPattern("MMMM", Locale.getDefault());
            monthText.setText(currentDisplayMonth.format(monthFormatter));

            DateTimeFormatter yearFormatter = DateTimeFormatter.ofPattern("yyyy", Locale.getDefault());
            yearText.setText(currentDisplayMonth.format(yearFormatter));
        } else {
            if (monthText == null) System.err.println("Error: monthText TextView not found!");
            if (yearText == null) System.err.println("Error: yearText TextView not found!");
        }
    }

    private void clearSelection() {
        tappedSelectedDate = null;
        if (previouslySelectedCellView != null) {
            removeSelectionStyle(previouslySelectedCellView);
            previouslySelectedCellView = null;
        }
    }

    private void drawCalendar() {
        if (currentDisplayMonth == null) {
            Log.e("CalendarError", "drawCalendar() called but currentDisplayMonth is null! Initializing to now.");
            currentDisplayMonth = LocalDate.now(); // Fallback, but points to a deeper issue
        }
            Log.d("CalendarLifecycle", "drawCalendar() called for month: " + currentDisplayMonth.toString()); // New Log
            calendarGrid.removeAllViews();
            cellDateMap.clear();
        }

        YearMonth yearMonth = YearMonth.from(currentDisplayMonth);
        int daysInMonth = yearMonth.lengthOfMonth();
        LocalDate firstOfMonth = currentDisplayMonth.withDayOfMonth(1);
        DayOfWeek firstDayOfWeekEnum = firstOfMonth.getDayOfWeek();
        int dayOfWeekOfFirst = (firstDayOfWeekEnum == DayOfWeek.SUNDAY) ? 0 : firstDayOfWeekEnum.getValue();

         {
        // Add empty cells for days before the first of the month
        for (int i = 0; i < dayOfWeekOfFirst; i++) {
            addCellToGrid(null, false, null);
        }

        // Add cells for each day of the month
        for (int day = 1; day <= daysInMonth; day++) {
            LocalDate cellDate = currentDisplayMonth.withDayOfMonth(day);
            Log.d("CalendarLifecycle", "drawCalendar() - about to call addCellToGrid for: " + cellDate);
            addCellToGrid(String.valueOf(day), true, cellDate);
        }

        // Optional: Fill remaining cells
        int cellsInTypicalGrid = 42; // 7 columns * 6 rows
        if (calendarGrid.getColumnCount() > 0 && calendarGrid.getRowCount() > 0) {
            cellsInTypicalGrid = calendarGrid.getColumnCount() * calendarGrid.getRowCount();
        }
        int currentCellCount = calendarGrid.getChildCount();
        for (int i = currentCellCount; i < cellsInTypicalGrid; i++) {
            addCellToGrid(null, false, null);
        }
    }

    private void addCellToGrid(final String text, boolean isDayCell, final LocalDate cellDate) {
        final TextView cell = new TextView(this);
        GridLayout.LayoutParams params = new GridLayout.LayoutParams(
                GridLayout.spec(GridLayout.UNDEFINED, 1f),
                GridLayout.spec(GridLayout.UNDEFINED, 1f)
        );
        params.width = 0;
        params.height = 0;
        // Consider setting margins in dp via XML styles or programmatically converting dp to pixels
        params.setMargins(2, 2, 2, 2);

        cell.setLayoutParams(params);
        cell.setGravity(Gravity.CENTER);
        cell.setPadding(10, 10, 10, 10);
        cell.setTextSize(15f); // Use TypedValue.COMPLEX_UNIT_SP for sp units

        if (isDayCell && cellDate != null) {
            cell.setText(text);
            cellDateMap.put(cell, cellDate);
            // Style for TODAY'S DATE //
            if (cellDate.equals(LocalDate.now())) {
                cell.setBackground(ContextCompat.getDrawable(this, R.drawable.date_circle_bg)); // White circle
                cell.setTextColor(ContextCompat.getColor(this, R.color.date_text_today_circled)); // Black text
                cell.setTypeface(null, Typeface.NORMAL); // Make today's date bold
            }

            LocalDate today = LocalDate.now();
            if (cellDate.equals(today)) {
                cell.setTextColor(ContextCompat.getColor(this, R.color.my_app_primary_color));
                cell.setTypeface(null, Typeface.BOLD);
            } else {
                cell.setTextColor(Color.BLACK);
                cell.setTypeface(null, Typeface.NORMAL);
            }

            if (cellDate.equals(tappedSelectedDate)) {
                applySelectionStyle(cell);
                previouslySelectedCellView = cell;
            } else {
                removeSelectionStyle(cell);
            }

            cell.setOnClickListener(v -> {
                if (previouslySelectedCellView != null) {
                    removeSelectionStyle(previouslySelectedCellView);
                }
                tappedSelectedDate = cellDateMap.get(cell);
                applySelectionStyle(cell);
                previouslySelectedCellView = cell;
            });
        } else {
            cell.setText("");
            cell.setClickable(false);
            cell.setBackground(null);
        }
        calendarGrid.addView(cell);
    }

    private void applySelectionStyle(TextView cell) {
        try {
            Drawable selectedBg = ContextCompat.getDrawable(this, R.drawable.selected_day_background);
            if (selectedBg != null) {
                cell.setBackground(selectedBg);
            } else {
                cell.setBackgroundColor(Color.LTGRAY);
            }
            // cell.setTextColor(Color.WHITE); // Optional
        } catch (Exception e) {
            cell.setBackgroundColor(Color.LTGRAY);
            System.err.println("Error applying selection style: " + e.getMessage());
        }
    }

    private void removeSelectionStyle(TextView cell) {
        cell.setBackground(null);
        LocalDate cellDate = cellDateMap.get(cell);
        if (cellDate != null) {
            if (cellDate.equals(LocalDate.now())) {
                cell.setTextColor(ContextCompat.getColor(this, R.color.my_app_primary_color));
                cell.setTypeface(null, Typeface.BOLD);
            } else {
                cell.setTextColor(Color.WHITE);
                cell.setTypeface(null, Typeface.NORMAL);
            }
        } else {
            cell.setTextColor(Color.WHITE);
            cell.setTypeface(null, Typeface.NORMAL);
        }
    }

}