/*
 * 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.JsonGenerationException;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.io.CharTypes;
import com.fasterxml.jackson.core.json.JsonWriteContext;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.module.SimpleModule;
import io.vertx.core.json.DecodeException;
import io.vertx.core.json.EncodeException;

import java.io.IOException;

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 final static ObjectMapper mapper;

  static {
    mapper = new ObjectMapper();

    // 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 adapted from http://wiki.fasterxml.com/JacksonSampleQuoteChars
    SimpleModule simpleModule = new SimpleModule();

    simpleModule.addSerializer(String.class, new JsonSerializer<String>() {
      final char[] HEX_CHARS = "0123456789abcdef".toCharArray();
      final int[] ESCAPE_CODES = CharTypes.get7BitOutputEscapes();

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

      @Override
      public void serialize(String str, JsonGenerator gen, SerializerProvider provider) throws IOException {
        int status = ((JsonWriteContext) gen.getOutputContext()).writeValue();
        switch (status) {
          case JsonWriteContext.STATUS_OK_AFTER_COLON:
            gen.writeRaw(':');
            break;
          case JsonWriteContext.STATUS_OK_AFTER_COMMA:
            gen.writeRaw(',');
            break;
          case JsonWriteContext.STATUS_EXPECT_NAME:
            throw new JsonGenerationException("Can not write string value here", gen);
        }
        gen.writeRaw('"');
        for (char c : str.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('"');
      }
    });
    mapper.registerModule(simpleModule);
  }

  public static String encode(Object obj) throws EncodeException {
    try {
      return mapper.writeValueAsString(obj);
    }
    catch (Exception e) {
      throw new EncodeException("Failed to encode as JSON");
    }
  }

  public static <T> T decodeValue(String str, Class<T> clazz) throws DecodeException {
    try {
      return mapper.readValue(str, clazz);
    }
    catch (Exception e) {
      throw new DecodeException("Failed to decode");
    }
  }
}