StackConverterGUI.java

import javax.swing.*;
import javax.swing.border.*;
import javax.swing.table.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;

/**
 * Lab 5 – Infix Expression Converter GUI
 *
 * Connects to the C back-end via JNI (StackConverter).
 * Features:
 *   • Convert infix → postfix and prefix
 *   • Handle +  -  *  /  ^  unary-minus  parentheses
 *   • Variable substitution and numeric evaluation
 *   • History list (last 5 conversions, stack-based undo/redo)
 */
public class StackConverterGUI extends JFrame {

    /* ── JNI bridge ── */
    private final StackConverter conv = new StackConverter();

    /* ── Input widgets ── */
    private JTextField infixField;
    private JTextArea  postfixArea;
    private JTextArea  prefixArea;
    private JTextArea  resultArea;

    /* ── Variable table ── */
    private DefaultTableModel varModel;

    /* ── History stack (max 5) ── */
    private final Deque<String[]> history    = new ArrayDeque<>();   // undo stack
    private final Deque<String[]> redoStack  = new ArrayDeque<>();   // redo stack
    private static final int MAX_HISTORY = 5;

    /* ── History display ── */
    private DefaultListModel<String> historyListModel;
    private JList<String>            historyList;

    /* ── Colour palette ── */
    private static final Color COL_BG      = new Color(245, 247, 252);
    private static final Color COL_HEADER  = new Color( 37,  99, 235);
    private static final Color COL_ACCENT  = new Color( 99, 102, 241);
    private static final Color COL_BTN_FG  = Color.WHITE;
    private static final Color COL_AREA_BG = new Color(250, 251, 255);
    private static final Font  MONO        = new Font("Monospaced", Font.PLAIN, 14);
    private static final Font  LABEL_FONT  = new Font("SansSerif", Font.BOLD, 12);

    /* ══════════════════════════════════════════════════════ */

    public StackConverterGUI() {
        super("Lab 5 – Infix Expression Converter (Java + C via JNI)");
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setSize(900, 700);
        setMinimumSize(new Dimension(780, 580));
        getContentPane().setBackground(COL_BG);
        setLayout(new BorderLayout(10, 10));

        add(buildHeader(),      BorderLayout.NORTH);
        add(buildCenter(),      BorderLayout.CENTER);
        add(buildSidePanel(),   BorderLayout.EAST);
        add(buildStatusBar(),   BorderLayout.SOUTH);

        setLocationRelativeTo(null);
        setVisible(true);
    }

    /* ─────────────────── Header ─────────────────── */

    private JPanel buildHeader() {
        JPanel p = new JPanel(new BorderLayout(8, 8));
        p.setBackground(COL_HEADER);
        p.setBorder(new EmptyBorder(14, 18, 14, 18));

        JLabel title = new JLabel("Infix Expression Converter  |  Stack Application");
        title.setFont(new Font("SansSerif", Font.BOLD, 18));
        title.setForeground(Color.WHITE);
        p.add(title, BorderLayout.WEST);

        JLabel subtitle = new JLabel("Data Structures Lab 5");
        subtitle.setFont(new Font("SansSerif", Font.ITALIC, 13));
        subtitle.setForeground(new Color(186, 230, 253));
        p.add(subtitle, BorderLayout.EAST);
        return p;
    }

    /* ─────────────────── Centre (input + output) ─────────────────── */

    private JPanel buildCenter() {
        JPanel p = new JPanel(new BorderLayout(8, 8));
        p.setBackground(COL_BG);
        p.setBorder(new EmptyBorder(8, 14, 8, 6));

        p.add(buildInputPanel(),   BorderLayout.NORTH);
        p.add(buildOutputPanel(),  BorderLayout.CENTER);
        p.add(buildEvalPanel(),    BorderLayout.SOUTH);
        return p;
    }

    private JPanel buildInputPanel() {
        JPanel p = new JPanel(new BorderLayout(8, 0));
        p.setBackground(COL_BG);
        p.setBorder(titled("Infix Expression"));

        infixField = new JTextField("a+b*c");
        infixField.setFont(MONO);
        infixField.setPreferredSize(new Dimension(0, 36));
        infixField.addActionListener(e -> doConvert());

        JButton btnConvert = styledBtn("Convert", COL_HEADER);
        btnConvert.addActionListener(e -> doConvert());

        JButton btnClear = styledBtn("Clear", new Color(107, 114, 128));
        btnClear.addActionListener(e -> {
            infixField.setText("");
            postfixArea.setText("");
            prefixArea.setText("");
            resultArea.setText("");
        });

        JPanel btnPanel = new JPanel(new FlowLayout(FlowLayout.RIGHT, 6, 0));
        btnPanel.setBackground(COL_BG);
        btnPanel.add(btnClear);
        btnPanel.add(btnConvert);

        p.add(new JLabel("  Enter expression: "), BorderLayout.WEST);
        p.add(infixField, BorderLayout.CENTER);
        p.add(btnPanel,   BorderLayout.EAST);
        return p;
    }

    private JPanel buildOutputPanel() {
        JPanel p = new JPanel(new GridLayout(1, 2, 10, 0));
        p.setBackground(COL_BG);
        p.setBorder(new EmptyBorder(4, 0, 4, 0));

        postfixArea = outputArea();
        prefixArea  = outputArea();

        p.add(labelledArea("Postfix  (~ = unary minus)", postfixArea));
        p.add(labelledArea("Prefix", prefixArea));
        return p;
    }

    private JPanel buildEvalPanel() {
        JPanel outer = new JPanel(new BorderLayout(8, 4));
        outer.setBackground(COL_BG);
        outer.setBorder(titled("Evaluate (enter variable values below)"));

        /* Variable table */
        String[] cols = { "Variable", "Value" };
        varModel = new DefaultTableModel(cols, 0) {
            @Override public boolean isCellEditable(int r, int c) { return true; }
        };
        for (char v : "abcdefghij".toCharArray())
            varModel.addRow(new Object[]{ String.valueOf(v), "" });

        JTable varTable = new JTable(varModel);
        varTable.setRowHeight(22);
        varTable.setFont(MONO);
        varTable.getTableHeader().setFont(LABEL_FONT);
        varTable.setGridColor(new Color(220, 225, 235));

        JScrollPane scroll = new JScrollPane(varTable);
        scroll.setPreferredSize(new Dimension(0, 120));
        outer.add(scroll, BorderLayout.CENTER);

        /* Evaluate button + result */
        JPanel bottom = new JPanel(new BorderLayout(8, 0));
        bottom.setBackground(COL_BG);

        JButton btnEval = styledBtn("Evaluate", COL_ACCENT);
        btnEval.addActionListener(e -> doEvaluate());

        resultArea = outputArea();
        resultArea.setPreferredSize(new Dimension(0, 36));

        bottom.add(btnEval,    BorderLayout.WEST);
        bottom.add(labelledArea("Result", resultArea), BorderLayout.CENTER);
        outer.add(bottom, BorderLayout.SOUTH);
        return outer;
    }

    /* ─────────────────── Side panel (history + undo/redo) ─────────────────── */

    private JPanel buildSidePanel() {
        JPanel p = new JPanel(new BorderLayout(4, 6));
        p.setBackground(COL_BG);
        p.setBorder(new CompoundBorder(
                new EmptyBorder(8, 0, 8, 14),
                titled("History (max 5)")));
        p.setPreferredSize(new Dimension(220, 0));

        historyListModel = new DefaultListModel<>();
        historyList = new JList<>(historyListModel);
        historyList.setFont(new Font("Monospaced", Font.PLAIN, 11));
        historyList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        historyList.addMouseListener(new MouseAdapter() {
            @Override public void mouseClicked(MouseEvent e) {
                if (e.getClickCount() == 2) restoreFromHistory();
            }
        });

        JScrollPane sp = new JScrollPane(historyList);
        p.add(sp, BorderLayout.CENTER);

        JPanel btnRow = new JPanel(new GridLayout(1, 2, 6, 0));
        btnRow.setBackground(COL_BG);

        JButton undo = styledBtn("Undo", new Color(202,  79,  79));
        JButton redo = styledBtn("Redo", new Color( 59, 130, 246));
        undo.addActionListener(e -> doUndo());
        redo.addActionListener(e -> doRedo());
        btnRow.add(undo);
        btnRow.add(redo);
        p.add(btnRow, BorderLayout.SOUTH);
        return p;
    }

    /* ─────────────────── Status bar ─────────────────── */

    private JLabel statusLabel;

    private JPanel buildStatusBar() {
        JPanel p = new JPanel(new FlowLayout(FlowLayout.LEFT, 14, 4));
        p.setBackground(new Color(230, 234, 245));
        statusLabel = new JLabel("Ready.  Double-click a history entry to restore it.");
        statusLabel.setFont(new Font("SansSerif", Font.PLAIN, 11));
        p.add(statusLabel);
        return p;
    }

    /* ══════════════════════════════════════════════════════ */
    /*  Actions                                               */
    /* ══════════════════════════════════════════════════════ */

    private void doConvert() {
        String infix = infixField.getText().trim();
        if (infix.isEmpty()) { status("Please enter an expression."); return; }

        String pf = conv.toPostfix(infix);
        String pr = conv.toPrefix(infix);

        postfixArea.setText(pf);
        prefixArea.setText(pr);
        resultArea.setText("");

        if (!pf.startsWith("ERROR")) {
            pushHistory(new String[]{ infix, pf, pr });
            status("Converted: " + infix);
        } else {
            status("Conversion error – check your expression.");
        }
    }

    private void doEvaluate() {
        String infix = infixField.getText().trim();
        if (infix.isEmpty()) { status("No expression to evaluate."); return; }

        /* Build variable string "a=1,b=2,..." from table */
        StringBuilder sb = new StringBuilder();
        for (int r = 0; r < varModel.getRowCount(); r++) {
            Object varObj = varModel.getValueAt(r, 0);
            Object valObj = varModel.getValueAt(r, 1);
            if (varObj == null || valObj == null) continue;
            String val = valObj.toString().trim();
            if (val.isEmpty()) continue;
            if (sb.length() > 0) sb.append(',');
            sb.append(varObj).append('=').append(val);
        }

        String result = conv.evaluate(infix, sb.toString());
        resultArea.setText(result);
        status(result.startsWith("ERROR") ? "Evaluation failed." :
               "Result = " + result);
    }

    /* ── History ── */

    private void pushHistory(String[] entry) {
        /* Push current state to undo stack */
        if (history.size() == MAX_HISTORY) history.pollFirst();
        history.offerLast(entry);
        redoStack.clear();
        refreshHistoryList();
    }

    private void refreshHistoryList() {
        historyListModel.clear();
        for (String[] e : history)
            historyListModel.addElement(e[0]);
        if (!historyListModel.isEmpty())
            historyList.setSelectedIndex(historyListModel.size() - 1);
    }

    private void restoreFromHistory() {
        int idx = historyList.getSelectedIndex();
        if (idx < 0) return;
        String[] entry = (String[]) history.toArray()[idx];
        infixField.setText(entry[0]);
        postfixArea.setText(entry[1]);
        prefixArea.setText(entry[2]);
        status("Restored: " + entry[0]);
    }

    private void doUndo() {
        if (history.isEmpty()) { status("Nothing to undo."); return; }
        String[] last = history.pollLast();
        redoStack.offerLast(last);
        refreshHistoryList();
        if (!history.isEmpty()) {
            String[] prev = history.peekLast();
            infixField.setText(prev[0]);
            postfixArea.setText(prev[1]);
            prefixArea.setText(prev[2]);
            status("Undo → " + prev[0]);
        } else {
            infixField.setText("");
            postfixArea.setText("");
            prefixArea.setText("");
            status("Undone all entries.");
        }
    }

    private void doRedo() {
        if (redoStack.isEmpty()) { status("Nothing to redo."); return; }
        String[] entry = redoStack.pollLast();
        if (history.size() == MAX_HISTORY) history.pollFirst();
        history.offerLast(entry);
        infixField.setText(entry[0]);
        postfixArea.setText(entry[1]);
        prefixArea.setText(entry[2]);
        refreshHistoryList();
        status("Redo → " + entry[0]);
    }

    /* ══════════════════════════════════════════════════════ */
    /*  UI helpers                                            */
    /* ══════════════════════════════════════════════════════ */

    private JTextArea outputArea() {
        JTextArea a = new JTextArea();
        a.setFont(MONO);
        a.setBackground(COL_AREA_BG);
        a.setEditable(false);
        a.setLineWrap(true);
        a.setWrapStyleWord(true);
        a.setBorder(new EmptyBorder(4, 6, 4, 6));
        return a;
    }

    private JPanel labelledArea(String label, JTextArea area) {
        JPanel p = new JPanel(new BorderLayout(0, 2));
        p.setBackground(COL_BG);
        JLabel l = new JLabel(label);
        l.setFont(LABEL_FONT);
        l.setForeground(new Color(75, 85, 99));
        p.add(l, BorderLayout.NORTH);
        p.add(new JScrollPane(area), BorderLayout.CENTER);
        return p;
    }

    private JButton styledBtn(String text, Color bg) {
        JButton b = new JButton(text);
        b.setBackground(bg);
        b.setForeground(COL_BTN_FG);
        b.setFont(new Font("SansSerif", Font.BOLD, 12));
        b.setFocusPainted(false);
        b.setBorder(new EmptyBorder(7, 16, 7, 16));
        b.setCursor(new Cursor(Cursor.HAND_CURSOR));
        b.setOpaque(true);                          // ← add this
        b.setContentAreaFilled(true);               // ← add this
        b.setUI(new javax.swing.plaf.basic.BasicButtonUI()); // ← add this
        return b;
    }

    private TitledBorder titled(String t) {
        TitledBorder tb = BorderFactory.createTitledBorder(
                BorderFactory.createLineBorder(new Color(209, 213, 219), 1), t);
        tb.setTitleFont(LABEL_FONT);
        tb.setTitleColor(COL_HEADER);
        return tb;
    }

    private void status(String msg) {
        statusLabel.setText(msg);
    }

    /* ══════════════════════════════════════════════════════ */

    public static void main(String[] args) {
        try { UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName()); }
        catch (Exception ignored) {}
        SwingUtilities.invokeLater(StackConverterGUI::new);
    }
}