/*******************************************************************************
 * Copyright (c) 2013, 2017 EclipseSource.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 ******************************************************************************/
package com.restfb.json;

import java.io.IOException;
import java.io.Serializable;
import java.io.StringWriter;
import java.io.Writer;
import java.util.Objects;

/**
 * Represents a JSON value. This can be a JSON <strong>object</strong>, an <strong> array</strong>, a
 * <strong>number</strong>, a <strong>string</strong>, or one of the literals
 * <strong>true</strong>, <strong>false</strong>, and <strong>null</strong>.
 * <p>
 * The literals <strong>true</strong>, <strong>false</strong>, and <strong>null</strong> are
 * represented by the constants {@link Json#TRUE}, {@link Json#FALSE}, and {@link Json#NULL}.
 * </p>
 * <p>
 * JSON <strong>objects</strong> and <strong>arrays</strong> are represented by the subtypes
 * {@link JsonObject} and {@link JsonArray}. Instances of these types can be created using the public constructors of these classes.
 * </p>
 * <p>
 * Instances that represent JSON <strong>numbers</strong>, <strong>strings</strong> and
 * <strong>boolean</strong> values can be created using the static factory methods
 * {@link Json#value(String)}, {@link Json#value(long)}, {@link Json#value(double)}, etc.
 * </p>
 * <p>
 * In order to find out whether an instance of this class is of a certain type, the methods
 * {@link #isObject()}, {@link #isArray()}, {@link #isString()}, {@link #isNumber()} etc. can be used.
 * </p>
 * <p>
 * If the type of a JSON value is known, the methods {@link #asObject()}, {@link #asArray()}, {@link #asString()},
 * {@link #asInt()}, etc. can be used to get this value directly in the appropriate target type.
 * </p>
 * <p>
 * This class is <strong>not supposed to be extended</strong> by clients.
 * </p>
 */
@SuppressWarnings("serial") // use default serial UID
public abstract class JsonValue implements Serializable {

  // String constants
  private static final String NOT_A_NUMBER = "Not a number: ";
  private static final String NOT_A_STRING = "Not a string: ";
  private static final String NOT_A_BOOLEAN = "Not a boolean: ";
  // String constants
  protected static final String STRING_IS_NULL = "string is null";
  protected static final String OBJECT_IS_NULL = "object is null";
  protected static final String NAME_IS_NULL = "name is null";
  protected static final String VALUE_IS_NULL = "value is null";
  protected static final String ARRAY_IS_NULL = "array is null";

  JsonValue() {
    // prevent subclasses outside of this package
  }

  /**
   * Detects whether this value represents a JSON object. If this is the case, this value is an instance of
   * {@link JsonObject}.
   *
   * @return <code>true</code> if this value is an instance of JsonObject
   */
  public boolean isObject() {
    return false;
  }

  /**
   * Detects whether this value represents a JSON array. If this is the case, this value is an instance of
   * {@link JsonArray}.
   *
   * @return <code>true</code> if this value is an instance of JsonArray
   */
  public boolean isArray() {
    return false;
  }

  /**
   * Detects whether this value represents a JSON number.
   *
   * @return <code>true</code> if this value represents a JSON number
   */
  public boolean isNumber() {
    return false;
  }

  /**
   * Detects whether this value represents a JSON string.
   *
   * @return <code>true</code> if this value represents a JSON string
   */
  public boolean isString() {
    return false;
  }

  /**
   * Detects whether this value represents a boolean value.
   *
   * @return <code>true</code> if this value represents either the JSON literal <code>true</code> or <code>false</code>
   */
  public boolean isBoolean() {
    return false;
  }

  /**
   * Detects whether this value represents the JSON literal <code>true</code>.
   *
   * @return <code>true</code> if this value represents the JSON literal <code>true</code>
   */
  public boolean isTrue() {
    return false;
  }

  /**
   * Detects whether this value represents the JSON literal <code>false</code>.
   *
   * @return <code>true</code> if this value represents the JSON literal <code>false</code>
   */
  public boolean isFalse() {
    return false;
  }

  /**
   * Detects whether this value represents the JSON literal <code>null</code>.
   *
   * @return <code>true</code> if this value represents the JSON literal <code>null</code>
   */
  public boolean isNull() {
    return false;
  }

  /**
   * Returns this JSON value as {@link JsonObject}, assuming that this value represents a JSON object. If this is not
   * the case, an exception is thrown.
   *
   * @return a JSONObject for this value
   * @throws UnsupportedOperationException
   *           if this value is not a JSON object
   */
  public JsonObject asObject() {
    throw new UnsupportedOperationException("Not an object: " + toString());
  }

  /**
   * Returns this JSON value as {@link JsonArray}, assuming that this value represents a JSON array. If this is not the
   * case, an exception is thrown.
   *
   * @return a JSONArray for this value
   * @throws UnsupportedOperationException
   *           if this value is not a JSON array
   */
  public JsonArray asArray() {
    throw new UnsupportedOperationException("Not an array: " + toString());
  }

  /**
   * Returns this JSON value as an <code>int</code> value, assuming that this value represents a JSON number that can be
   * interpreted as Java <code>int</code>. If this is not the case, an exception is thrown.
   * <p>
   * To be interpreted as Java <code>int</code>, the JSON number must neither contain an exponent nor a fraction part.
   * Moreover, the number must be in the <code>Integer</code> range.
   * </p>
   *
   * @return this value as <code>int</code>
   * @throws UnsupportedOperationException
   *           if this value is not a JSON number
   * @throws NumberFormatException
   *           if this JSON number can not be interpreted as <code>int</code> value
   */
  public int asInt() {
    throw new UnsupportedOperationException(NOT_A_NUMBER + toString());
  }

  /**
   * Returns this JSON value as a <code>long</code> value, assuming that this value represents a JSON number that can be
   * interpreted as Java <code>long</code>. If this is not the case, an exception is thrown.
   * <p>
   * To be interpreted as Java <code>long</code>, the JSON number must neither contain an exponent nor a fraction part.
   * Moreover, the number must be in the <code>Long</code> range.
   * </p>
   *
   * @return this value as <code>long</code>
   * @throws UnsupportedOperationException
   *           if this value is not a JSON number
   * @throws NumberFormatException
   *           if this JSON number can not be interpreted as <code>long</code> value
   */
  public long asLong() {
    throw new UnsupportedOperationException(NOT_A_NUMBER + toString());
  }

  /**
   * Returns this JSON value as a <code>float</code> value, assuming that this value represents a JSON number. If this
   * is not the case, an exception is thrown.
   * <p>
   * If the JSON number is out of the <code>Float</code> range, {@link Float#POSITIVE_INFINITY} or
   * {@link Float#NEGATIVE_INFINITY} is returned.
   * </p>
   *
   * @return this value as <code>float</code>
   * @throws UnsupportedOperationException
   *           if this value is not a JSON number
   */
  public float asFloat() {
    throw new UnsupportedOperationException(NOT_A_NUMBER + toString());
  }

  /**
   * Returns this JSON value as a <code>double</code> value, assuming that this value represents a JSON number. If this
   * is not the case, an exception is thrown.
   * <p>
   * If the JSON number is out of the <code>Double</code> range, {@link Double#POSITIVE_INFINITY} or
   * {@link Double#NEGATIVE_INFINITY} is returned.
   * </p>
   *
   * @return this value as <code>double</code>
   * @throws UnsupportedOperationException
   *           if this value is not a JSON number
   */
  public double asDouble() {
    throw new UnsupportedOperationException(NOT_A_NUMBER + toString());
  }

  /**
   * Returns this JSON value as String, assuming that this value represents a JSON string. If this is not the case, an
   * exception is thrown.
   *
   * @return the string represented by this value
   * @throws UnsupportedOperationException
   *           if this value is not a JSON string
   */
  public String asString() {
    throw new UnsupportedOperationException(NOT_A_STRING + toString());
  }

  /**
   * Returns this JSON value as a <code>boolean</code> value, assuming that this value is either <code>true</code> or
   * <code>false</code>. If this is not the case, an exception is thrown.
   *
   * @return this value as <code>boolean</code>
   * @throws UnsupportedOperationException
   *           if this value is neither <code>true</code> or <code>false</code>
   */
  public boolean asBoolean() {
    throw new UnsupportedOperationException(NOT_A_BOOLEAN + toString());
  }

  /**
   * Writes the JSON representation of this value to the given writer in its minimal form, without any additional
   * whitespace.
   * <p>
   * Writing performance can be improved by using a {@link java.io.BufferedWriter BufferedWriter}.
   * </p>
   *
   * @param writer
   *          the writer to write this value to
   * @throws IOException
   *           if an I/O error occurs in the writer
   */
  public void writeTo(Writer writer) throws IOException {
    writeTo(writer, WriterConfig.MINIMAL);
  }

  /**
   * Writes the JSON representation of this value to the given writer using the given formatting.
   * <p>
   * Writing performance can be improved by using a {@link java.io.BufferedWriter BufferedWriter}.
   * </p>
   *
   * @param writer
   *          the writer to write this value to
   * @param config
   *          a configuration that controls the formatting or <code>null</code> for the minimal form
   * @throws IOException
   *           if an I/O error occurs in the writer
   */
  public void writeTo(Writer writer, WriterConfig config) throws IOException {
    Objects.requireNonNull(writer, "writer is null");
    Objects.requireNonNull(config, "config is null");
    WritingBuffer buffer = new WritingBuffer(writer, 128);
    write(config.createWriter(buffer));
    buffer.flush();
  }

  /**
   * Returns the JSON string for this value in its minimal form, without any additional whitespace.
   * The result is guaranteed to be a valid input for the method {@link Json#parse(String)} and to
   * create a value that is <em>equal</em> to this object.
   *
   * @return a JSON string that represents this value
   */
  @Override
  public String toString() {
    return toString(WriterConfig.UNICODE);
  }

  /**
   * Returns the JSON string for this value using the given formatting.
   *
   * @param config
   *          a configuration that controls the formatting or <code>null</code> for the minimal form
   * @return a JSON string that represents this value
   */
  public String toString(WriterConfig config) {
    StringWriter writer = new StringWriter();
    try {
      writeTo(writer, config);
    } catch (IOException exception) {
      // StringWriter does not throw IOExceptions
      throw new RuntimeException(exception);
    }
    return writer.toString();
  }

  /**
   * Indicates whether some other object is "equal to" this one according to the contract specified in
   * {@link Object#equals(Object)}.
   * <p>
   * Two JsonValues are considered equal if and only if they represent the same JSON text. As a consequence, two given
   * JsonObjects may be different even though they contain the same set of names with the same values, but in a
   * different order.
   * </p>
   *
   * @param object
   *          the reference object with which to compare
   * @return true if this object is the same as the object argument; false otherwise
   */
  @Override
  public boolean equals(Object object) {
    return super.equals(object);
  }

  @Override
  public int hashCode() {
    return super.hashCode();
  }

  abstract void write(JsonWriter writer) throws IOException;

}