/*

 * Copyright (c) 2015, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

package jdk.internal.jshell.tool;

import java.io.IOException;

import java.io.InputStream;

import java.util.function.Consumer;

public final class StopDetectingInputStream extends InputStream {

    public static final int INITIAL_SIZE = 128;

    private final Runnable stop;

    private final Consumer<Exception> errorHandler;

    private boolean initialized;

    private int[] buffer = new int[INITIAL_SIZE];

    private int start;

    private int end;

    private State state = State.WAIT;

    public StopDetectingInputStream(Runnable stop, Consumer<Exception> errorHandler) {

        this.stop = stop;

        this.errorHandler = errorHandler;

    }

    public synchronized InputStream setInputStream(InputStream input) {

        if (initialized)

            throw new IllegalStateException("Already initialized.");

        initialized = true;

        Thread reader = new Thread(() -> {

            try {

                int read;

                while (true) {

                    //to support external terminal editors, the "cmdin.read" must not run when

                    //an external editor is running. At the same time, it needs to run while the

                    //user's code is running (so Ctrl-C is detected). Hence waiting here until

                    //there is a confirmed need for input.

                    State currentState = waitInputNeeded();

                    if (currentState == State.CLOSED) {

                        break;

                    }

                    if ((read = input.read()) == (-1)) {

                        break;

                    }

                    if (read == 3 && getState() == State.BUFFER) {

                        stop.run();

                    } else {

                        write(read);

                    }

                }

            } catch (IOException ex) {

                errorHandler.accept(ex);

            } finally {

                shutdown();

            }

        });

        reader.setDaemon(true);

        reader.start();

        return this;

    }

    @Override

    public synchronized int read() {

        while (start == end) {

            if (state == State.CLOSED) {

                return -1;

            }

            if (state == State.WAIT) {

                state = State.READ;

            }

            notifyAll();

            try {

                wait();

            } catch (InterruptedException ex) {

                //ignore

            }

        }

        try {

            return buffer[start];

        } finally {

            start = (start + 1) % buffer.length;

        }

    }

    public synchronized void shutdown() {

        state = State.CLOSED;

        notifyAll();

    }

    public synchronized void write(int b) {

            state = State.WAIT;

        }

        int newEnd = (end + 1) % buffer.length;

        if (newEnd == start) {

            //overflow:

            int[] newBuffer = new int[buffer.length * 2];

            int rightPart = (end > start ? end : buffer.length) - start;

            int leftPart = end > start ? 0 : start - 1;

            System.arraycopy(buffer, start, newBuffer, 0, rightPart);

            System.arraycopy(buffer, 0, newBuffer, rightPart, leftPart);

            buffer = newBuffer;

            start = 0;

            end = rightPart + leftPart;

            newEnd = end + 1;

        }

        buffer[end] = b;

        end = newEnd;

        notifyAll();

    }

    public synchronized void setState(State state) {

        if (this.state != State.CLOSED) {

            this.state = state;

            notifyAll();

        }

    }

    private synchronized State getState() {

        return state;

    }

    private synchronized State waitInputNeeded() {

        while (state == State.WAIT) {

            try {

                wait();

            } catch (InterruptedException ex) {

                //ignore

            }

        }

        return state;

    }

    public enum State {

        /* No reading from the input should happen. This is the default state. The StopDetectingInput

         * must be in this state when an external editor is being run, so that the external editor

         * can read from the input.

         */

        WAIT,

        /* A single input character should be read. Reading from the StopDetectingInput will move it

         * into this state, and the state will be automatically changed back to WAIT when a single

         * input character is obtained. This state is typically used while the user is editing the

         * input line.

         */

        READ,

        /* Continuously read from the input. Forward Ctrl-C ((int) 3) to the "stop" Runnable, buffer

         * all other input. This state is typically used while the user's code is running, to provide

         * the ability to detect Ctrl-C in order to stop the execution.

         */

        BUFFER,

        /* The input is closed.

        */

        CLOSED

    }

}