/*
 * Copyright 2014 Red Hat, Inc.
 *
 *  All rights reserved. This program and the accompanying materials
 *  are made available under the terms of the Eclipse Public License v1.0
 *  and Apache License v2.0 which accompanies this distribution.
 *
 *  The Eclipse Public License is available at
 *  http://www.eclipse.org/legal/epl-v10.html
 *
 *  The Apache License v2.0 is available at
 *  http://www.opensource.org/licenses/apache2.0.php
 *
 *  You may elect to redistribute this code under either of these licenses.
 */

/*
 * Copyright (c) 2011-2013 The original author or authors
 * ------------------------------------------------------
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * and Apache License v2.0 which accompanies this distribution.
 *
 *     The Eclipse Public License is available at
 *     http://www.eclipse.org/legal/epl-v10.html
 *
 *     The Apache License v2.0 is available at
 *     http://www.opensource.org/licenses/apache2.0.php
 *
 * You may elect to redistribute this code under either of these licenses.
 */

package io.vertx.ext.web.handler.sockjs.impl;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.core.io.CharTypes;
import io.vertx.core.json.EncodeException;

import java.io.IOException;
import java.io.StringWriter;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

SockJS requires a special JSON codec - it requires that many other characters,
over and above what is required by the JSON spec are escaped.
To satisfy this we escape any character that escapable with short escapes and
any other non ASCII character we unicode escape it
Author:
Tim Fox, Paulo Lopes/**
 *
 * SockJS requires a special JSON codec - it requires that many other characters,
 * over and above what is required by the JSON spec are escaped.
 * To satisfy this we escape any character that escapable with short escapes and
 * any other non ASCII character we unicode escape it
 *
 * @author <a href="http://tfox.org">Tim Fox</a>
 * @author <a href="mailto:plopes@redhat.com">Paulo Lopes</a>
 */
public class JsonCodec {

  private static final JsonFactory factory = new JsonFactory();

  // By default, Jackson does not escape unicode characters in JSON strings
  // This should be ok, since a valid JSON string can contain unescaped JSON
  // characters.
  // However, SockJS requires that many unicode chars are escaped. This may
  // be due to browsers barfing over certain unescaped characters
  // So... when encoding strings we make sure all unicode chars are escaped

  // This code was adapted from http://wiki.fasterxml.com/JacksonSampleQuoteChars

  private static final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
  private static final int[] ESCAPE_CODES = CharTypes.get7BitOutputEscapes();

  private static void writeUnicodeEscape(JsonGenerator gen, char c) throws IOException {
    gen.writeRaw('\\');
    gen.writeRaw('u');
    gen.writeRaw(HEX_CHARS[(c >> 12) & 0xF]);
    gen.writeRaw(HEX_CHARS[(c >> 8) & 0xF]);
    gen.writeRaw(HEX_CHARS[(c >> 4) & 0xF]);
    gen.writeRaw(HEX_CHARS[c & 0xF]);
  }

  private static void writeShortEscape(JsonGenerator gen, char c) throws IOException {
    gen.writeRaw('\\');
    gen.writeRaw(c);
  }

  public static String encode(String[] messages) throws EncodeException {
    StringWriter sw = new StringWriter();
    try (JsonGenerator gen = factory.createGenerator(sw)) {
      gen.writeStartArray();
      boolean first = true;
      for (String message : messages) {
        if (first) {
          first = false;
        } else {
          gen.writeRaw(',');
        }
        gen.writeRaw('"');
        for (char c : message.toCharArray()) {
          if (c >= 0x80) writeUnicodeEscape(gen, c); // use generic escaping for all non US-ASCII characters
          else {
            // use escape table for first 128 characters
            int code = (c < ESCAPE_CODES.length ? ESCAPE_CODES[c] : 0);
            if (code == 0) gen.writeRaw(c); // no escaping
            else if (code == -1) writeUnicodeEscape(gen, c); // generic escaping
            else writeShortEscape(gen, (char) code); // short escaping (\n \t ...)
          }
        }
        gen.writeRaw('"');
      }
      gen.writeEndArray();
      gen.close();
      return sw.toString();
    } catch (Exception e) {
      throw new EncodeException("Failed to encode as JSON", e);
    }
  }

  public static List<String> decodeValues(String messages) {
    List<String> result = null;
    try (JsonParser parser = factory.createParser(messages)) {
      JsonToken jsonToken = parser.nextToken();
      if (jsonToken == JsonToken.START_ARRAY) {
        while (parser.nextToken() != JsonToken.END_ARRAY) {
          if (result == null) {
            result = new ArrayList<>();
          }
          result.add(parser.getValueAsString());
        }
      } else if (jsonToken == JsonToken.VALUE_STRING) {
        result = Collections.singletonList(parser.getValueAsString());
      }
      return result != null ? result : Collections.emptyList();
    } catch (Exception ignore) {
      return null;
    }
  }
}