/*

 * Copyright (c) 2017, 2018, 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.

 */

import java.net.ProtocolException;

import java.nio.ByteBuffer;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Locale;

import java.util.Map;

import static java.lang.String.format;

import static java.util.Objects.requireNonNull;

class Http1HeaderParser {

    private static final char CR = '\r';

    private static final char LF = '\n';

    private static final char HT = '\t';

    private static final char SP = ' ';

    private StringBuilder sb = new StringBuilder();

    private String statusLine;

    private int responseCode;

    private HttpHeaders headers;

    private Map<String,List<String>> privateMap = new HashMap<>();

    enum State { STATUS_LINE,

                 STATUS_LINE_FOUND_CR,

                 STATUS_LINE_END,

                 STATUS_LINE_END_CR,

                 HEADER,

                 HEADER_FOUND_CR,

                 HEADER_FOUND_LF,

                 HEADER_FOUND_CR_LF,

                 HEADER_FOUND_CR_LF_CR,

                 FINISHED }

    private State state = State.STATUS_LINE;

    /** Returns the status-line. */

    String statusLine() { return statusLine; }

    /** Returns the response code. */

    int responseCode() { return responseCode; }

    /** Returns the headers, possibly empty. */

    HttpHeaders headers() { assert state == State.FINISHED; return headers; }

    /**

     * Parses HTTP/1.X status-line and headers from the given bytes. Must be

     * called successive times, with additional data, until returns true.

     *

     * All given ByteBuffers will be consumed, until ( possibly ) the last one

     * ( when true is returned ), which may not be fully consumed.

     *

     * @param input the ( partial ) header data

     * @return true iff the end of the headers block has been reached

     */

    boolean parse(ByteBuffer input) throws ProtocolException {

        requireNonNull(input, "null input");

        while (input.hasRemaining() && state != State.FINISHED) {

            switch (state) {

                case STATUS_LINE:

                    readResumeStatusLine(input);

                    break;

                case STATUS_LINE_FOUND_CR:

                    readStatusLineFeed(input);

                    break;

                case STATUS_LINE_END:

                    maybeStartHeaders(input);

                    break;

                case STATUS_LINE_END_CR:

                    maybeEndHeaders(input);

                    break;

                case HEADER:

                    readResumeHeader(input);

                    break;

                // fallthrough

                case HEADER_FOUND_CR:

                case HEADER_FOUND_LF:

                    resumeOrLF(input);

                    break;

                case HEADER_FOUND_CR_LF:

                    resumeOrSecondCR(input);

                    break;

                case HEADER_FOUND_CR_LF_CR:

                    resumeOrEndHeaders(input);

                    break;

                default:

                    throw new InternalError(

                            "Unexpected state: " + String.valueOf(state));

            }

        }

        return state == State.FINISHED;

    }

    private void readResumeStatusLine(ByteBuffer input) {

        char c = 0;

        while (input.hasRemaining() && (c =(char)input.get()) != CR) {

            sb.append(c);

        }

        if (c == CR) {

            state = State.STATUS_LINE_FOUND_CR;

        }

    }

    private void readStatusLineFeed(ByteBuffer input) throws ProtocolException {

        char c = (char)input.get();

        if (c != LF) {

            throw protocolException("Bad trailing char, \"%s\", when parsing status-line, \"%s\"",

                                    c, sb.toString());

        }

        statusLine = sb.toString();

        sb = new StringBuilder();

        if (!statusLine.startsWith("HTTP/1.")) {

            throw protocolException("Invalid status line: \"%s\"", statusLine);

        }

        if (statusLine.length() < 12) {

            throw protocolException("Invalid status line: \"%s\"", statusLine);

        }

        responseCode = Integer.parseInt(statusLine.substring(9, 12));

        state = State.STATUS_LINE_END;

    }

    private void maybeStartHeaders(ByteBuffer input) {

        assert state == State.STATUS_LINE_END;

        assert sb.length() == 0;

        char c = (char)input.get();

        if (c == CR) {

            state = State.STATUS_LINE_END_CR;

        } else {

            sb.append(c);

            state = State.HEADER;

        }

    }

    private void maybeEndHeaders(ByteBuffer input) throws ProtocolException {

        assert state == State.STATUS_LINE_END_CR;

        assert sb.length() == 0;

        char c = (char)input.get();

        if (c == LF) {

            headers = ImmutableHeaders.of(privateMap);

            privateMap = null;

            state = State.FINISHED;  // no headers

        } else {

            throw protocolException("Unexpected \"%s\", after status-line CR", c);

        }

    }

    private void readResumeHeader(ByteBuffer input) {

        assert state == State.HEADER;

        assert input.hasRemaining();

        while (input.hasRemaining()) {

            char c = (char)input.get();

            if (c == CR) {

                state = State.HEADER_FOUND_CR;

                break;

            } else if (c == LF) {

                state = State.HEADER_FOUND_LF;

                break;

            }

            if (c == HT)

                c = SP;

            sb.append(c);

        }

    }

    private void addHeaderFromString(String headerString) {

        assert sb.length() == 0;

        int idx = headerString.indexOf(':');

        if (idx == -1)

            return;

        String name = headerString.substring(0, idx).trim();

        if (name.isEmpty())

            return;

        String value = headerString.substring(idx + 1, headerString.length()).trim();

        privateMap.computeIfAbsent(name.toLowerCase(Locale.US),

                                   k -> new ArrayList<>()).add(value);

    }

    private void resumeOrLF(ByteBuffer input) {

        assert state == State.HEADER_FOUND_CR || state == State.HEADER_FOUND_LF;

        char c = (char)input.get();

        if (c == LF && state == State.HEADER_FOUND_CR) {

            // header value will be flushed by

            // resumeOrSecondCR if next line does not

            // begin by SP or HT

            state = State.HEADER_FOUND_CR_LF;

        } else if (c == SP || c == HT) {

            sb.append(SP); // parity with MessageHeaders

            state = State.HEADER;

        } else {

            sb = new StringBuilder();

            sb.append(c);

            state = State.HEADER;

        }

    }

    private void resumeOrSecondCR(ByteBuffer input) {

        assert state == State.HEADER_FOUND_CR_LF;

        char c = (char)input.get();

        if (c == CR) {

            if (sb.length() > 0) {

                // no continuation line - flush

                // previous header value.

                String headerString = sb.toString();

                sb = new StringBuilder();

                addHeaderFromString(headerString);

            }

            state = State.HEADER_FOUND_CR_LF_CR;

        } else if (c == SP || c == HT) {

            assert sb.length() != 0;

            sb.append(SP); // continuation line

            state = State.HEADER;

        } else {

            if (sb.length() > 0) {

                // no continuation line - flush

                // previous header value.

                String headerString = sb.toString();

                sb = new StringBuilder();

                addHeaderFromString(headerString);

            }

            sb.append(c);

            state = State.HEADER;

        }

    }

    private void resumeOrEndHeaders(ByteBuffer input) throws ProtocolException {

        assert state == State.HEADER_FOUND_CR_LF_CR;

        char c = (char)input.get();

        if (c == LF) {

            state = State.FINISHED;

            headers = ImmutableHeaders.of(privateMap);

            privateMap = null;

        } else {

            throw protocolException("Unexpected \"%s\", after CR LF CR", c);

        }

    }

    private ProtocolException protocolException(String format, Object... args) {

        return new ProtocolException(format(format, args));

    }

}