/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */

package io.netty.handler.codec.http;

import io.netty.buffer.ByteBuf;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public final class HttpHeaderUtil {

    /**
     * Returns {@code true} if and only if the connection can remain open and
     * thus 'kept alive'.  This methods respects the value of the
     * {@code "Connection"} header first and then the return value of
     * {@link HttpVersion#isKeepAliveDefault()}.
     */
    public static boolean isKeepAlive(HttpMessage message) {
        CharSequence connection = message.headers().get(HttpHeaderNames.CONNECTION);
        if (connection != null && HttpHeaderValues.CLOSE.equalsIgnoreCase(connection)) {
            return false;
        }

        if (message.protocolVersion().isKeepAliveDefault()) {
            return !HttpHeaderValues.CLOSE.equalsIgnoreCase(connection);
        } else {
            return HttpHeaderValues.KEEP_ALIVE.equalsIgnoreCase(connection);
        }
    }

    /**
     * Sets the value of the {@code "Connection"} header depending on the
     * protocol version of the specified message.  This getMethod sets or removes
     * the {@code "Connection"} header depending on what the default keep alive
     * mode of the message's protocol version is, as specified by
     * {@link HttpVersion#isKeepAliveDefault()}.
     * <ul>
     * <li>If the connection is kept alive by default:
     *     <ul>
     *     <li>set to {@code "close"} if {@code keepAlive} is {@code false}.</li>
     *     <li>remove otherwise.</li>
     *     </ul></li>
     * <li>If the connection is closed by default:
     *     <ul>
     *     <li>set to {@code "keep-alive"} if {@code keepAlive} is {@code true}.</li>
     *     <li>remove otherwise.</li>
     *     </ul></li>
     * </ul>
     */
    public static void setKeepAlive(HttpMessage message, boolean keepAlive) {
        HttpHeaders h = message.headers();
        if (message.protocolVersion().isKeepAliveDefault()) {
            if (keepAlive) {
                h.remove(HttpHeaderNames.CONNECTION);
            } else {
                h.set(HttpHeaderNames.CONNECTION, HttpHeaderValues.CLOSE);
            }
        } else {
            if (keepAlive) {
                h.set(HttpHeaderNames.CONNECTION, HttpHeaderValues.KEEP_ALIVE);
            } else {
                h.remove(HttpHeaderNames.CONNECTION);
            }
        }
    }

    /**
     * Returns the length of the content.  Please note that this value is
     * not retrieved from {@link HttpContent#content()} but from the
     * {@code "Content-Length"} header, and thus they are independent from each
     * other.
     *
     * @return the content length
     *
     * @throws NumberFormatException
     *         if the message does not have the {@code "Content-Length"} header
     *         or its value is not a number
     */
    public static long getContentLength(HttpMessage message) {
        String value = message.headers().get(HttpHeaderNames.CONTENT_LENGTH);
        if (value != null) {
            return Long.parseLong(value);
        }

        // We know the content length if it's a Web Socket message even if
        // Content-Length header is missing.
        long webSocketContentLength = getWebSocketContentLength(message);
        if (webSocketContentLength >= 0) {
            return webSocketContentLength;
        }

        // Otherwise we don't.
        throw new NumberFormatException("header not found: " + HttpHeaderNames.CONTENT_LENGTH);
    }

    /**
     * Returns the length of the content.  Please note that this value is
     * not retrieved from {@link HttpContent#content()} but from the
     * {@code "Content-Length"} header, and thus they are independent from each
     * other.
     *
     * @return the content length or {@code defaultValue} if this message does
     *         not have the {@code "Content-Length"} header or its value is not
     *         a number
     */
    public static long getContentLength(HttpMessage message, long defaultValue) {
        String value = message.headers().get(HttpHeaderNames.CONTENT_LENGTH);
        if (value != null) {
            return Long.parseLong(value);
        }

        // We know the content length if it's a Web Socket message even if
        // Content-Length header is missing.
        long webSocketContentLength = getWebSocketContentLength(message);
        if (webSocketContentLength >= 0) {
            return webSocketContentLength;
        }

        // Otherwise we don't.
        return defaultValue;
    }

    /**
     * Returns the content length of the specified web socket message.  If the
     * specified message is not a web socket message, {@code -1} is returned.
     */
    private static int getWebSocketContentLength(HttpMessage message) {
        // WebSockset messages have constant content-lengths.
        HttpHeaders h = message.headers();
        if (message instanceof HttpRequest) {
            HttpRequest req = (HttpRequest) message;
            if (HttpMethod.GET.equals(req.method()) &&
                    h.contains(HttpHeaderNames.SEC_WEBSOCKET_KEY1) &&
                    h.contains(HttpHeaderNames.SEC_WEBSOCKET_KEY2)) {
                return 8;
            }
        } else if (message instanceof HttpResponse) {
            HttpResponse res = (HttpResponse) message;
            if (res.status().code() == 101 &&
                    h.contains(HttpHeaderNames.SEC_WEBSOCKET_ORIGIN) &&
                    h.contains(HttpHeaderNames.SEC_WEBSOCKET_LOCATION)) {
                return 16;
            }
        }

        // Not a web socket message
        return -1;
    }

    /**
     * Sets the {@code "Content-Length"} header.
     */
    public static void setContentLength(HttpMessage message, long length) {
        message.headers().set(HttpHeaderNames.CONTENT_LENGTH, length);
    }

    public static boolean isContentLengthSet(HttpMessage m) {
        return m.headers().contains(HttpHeaderNames.CONTENT_LENGTH);
    }

    /**
     * Returns {@code true} if and only if the specified message contains the
     * {@code "Expect: 100-continue"} header.
     */
    public static boolean is100ContinueExpected(HttpMessage message) {
        // Expect: 100-continue is for requests only.
        if (!(message instanceof HttpRequest)) {
            return false;
        }

        // It works only on HTTP/1.1 or later.
        if (message.protocolVersion().compareTo(HttpVersion.HTTP_1_1) < 0) {
            return false;
        }

        // In most cases, there will be one or zero 'Expect' header.
        CharSequence value = message.headers().get(HttpHeaderNames.EXPECT);
        if (value == null) {
            return false;
        }
        if (HttpHeaderValues.CONTINUE.equalsIgnoreCase(value)) {
            return true;
        }

        // Multiple 'Expect' headers.  Search through them.
        return message.headers().contains(HttpHeaderNames.EXPECT, HttpHeaderValues.CONTINUE, true);
    }

    /**
     * Sets or removes the {@code "Expect: 100-continue"} header to / from the
     * specified message.  If the specified {@code value} is {@code true},
     * the {@code "Expect: 100-continue"} header is set and all other previous
     * {@code "Expect"} headers are removed.  Otherwise, all {@code "Expect"}
     * headers are removed completely.
     */
    public static void set100ContinueExpected(HttpMessage message, boolean expected) {
        if (expected) {
            message.headers().set(HttpHeaderNames.EXPECT, HttpHeaderValues.CONTINUE);
        } else {
            message.headers().remove(HttpHeaderNames.EXPECT);
        }
    }

    /**
     * Checks to see if the transfer encoding in a specified {@link HttpMessage} is chunked
     *
     * @param message The message to check
     * @return True if transfer encoding is chunked, otherwise false
     */
    public static boolean isTransferEncodingChunked(HttpMessage message) {
        return message.headers().contains(HttpHeaderNames.TRANSFER_ENCODING, HttpHeaderValues.CHUNKED, true);
    }

    public static void setTransferEncodingChunked(HttpMessage m, boolean chunked) {
        if (chunked) {
            m.headers().add(HttpHeaderNames.TRANSFER_ENCODING, HttpHeaderValues.CHUNKED);
            m.headers().remove(HttpHeaderNames.CONTENT_LENGTH);
        } else {
            // Make a copy to be able to modify values while iterating
            List<String> encodings = m.headers().getAll(HttpHeaderNames.TRANSFER_ENCODING);
            if (encodings.isEmpty()) {
                return;
            }
            List<CharSequence> values = new ArrayList<CharSequence>(encodings);
            Iterator<CharSequence> valuesIt = values.iterator();
            while (valuesIt.hasNext()) {
                CharSequence value = valuesIt.next();
                if (HttpHeaderValues.CHUNKED.equalsIgnoreCase(value)) {
                    valuesIt.remove();
                }
            }
            if (values.isEmpty()) {
                m.headers().remove(HttpHeaderNames.TRANSFER_ENCODING);
            } else {
                m.headers().set(HttpHeaderNames.TRANSFER_ENCODING, values);
            }
        }
    }

    static void encodeAscii0(CharSequence seq, ByteBuf buf) {
        int length = seq.length();
        for (int i = 0 ; i < length; i++) {
            buf.writeByte(c2b(seq.charAt(i)));
        }
    }

    private static byte c2b(char c) {
        if (c > 255) {
            return '?';
        }
        return (byte) c;
    }

    private HttpHeaderUtil() { }
}