ast.js

export const nodeTypes = {
  DOCUMENT : 'document',
  COMMENT : 'comment',
  OBJECT : 'object',
  PROPERTY : 'property',
  KEY : 'key',
  ARRAY : 'array',
  VALUE : 'value',
  STRING : 'string',
  NUMBER : 'number',
  TRUE : 'true',
  FALSE : 'false',
  NULL : 'null',
  ERROR : 'error'
};

// All elements in the tree will extend the `JsonNode` base class
export class JsonNode {
  constructor(_type = nodeTypes.ERROR) {
    this._type = _type || nodeTypes.ERROR;
    this._position = null;
  }

  get type() { return this._type; }

  set position(_pos) { this._position = _pos || null; }

  get position() { return this._position; }

  accept(visitor) { visitor.visit(this); }

  static toObject(jsonNode) { return JSON.parse(JSON.stringify(jsonNode)); }

  static toString(jsonNode) { return JSON.stringify(jsonNode); }

  static toJSON(jsonNode) { return toJSON(jsonNode); }
};

export class JsonDocument extends JsonNode {
  constructor() {
    super(nodeTypes.DOCUMENT);
    this._child = null;
    this._comments = [];
  }

  set child(_child) { this._child = _child; }

  get child() { return this._child; }

  get comments() { return this._comments; }
};

export class JsonObject extends JsonNode {
  constructor() {
    super(nodeTypes.OBJECT);
    this._properties = [];
    this._comments = [];
  }

  get properties() { return this._properties; }

  get comments() { return this._comments; }
};

export class JsonProperty extends JsonNode {
  constructor() {
    super(nodeTypes.PROPERTY);
    this._key = null;
    this._value = null;
  }

  get key() { return this._key; }

  set key(_key) { this._key = _key; }

  get value() { return this._value; }

  set value(_value) { this._value = _value; }
};

export class JsonArray extends JsonNode {
  constructor() {
    super(nodeTypes.ARRAY);
    this._items = [];
    this._comments = [];
  }

  get items() { return this._items; }

  get comments() { return this._comments; }
};

export class JsonValue extends JsonNode {
  constructor(_value = null, _type = nodeTypes.VALUE) {
    super(_type);
    this._value = _value;
  };

  get value() { return this._value; }

  set value(_value) { this._value = _value; }
};

export class JsonKey extends JsonValue {
  constructor(_value = null) { super(_value, nodeTypes.KEY); };
};

export class JsonComment extends JsonValue {
  constructor(_value = null) { super(_value, nodeTypes.COMMENT); }
};

export class JsonString extends JsonValue {
  constructor(_value = null) { super(_value, nodeTypes.STRING); }
};

export class JsonNumber extends JsonValue {
  constructor(_value = null) { super(_value, nodeTypes.NUMBER); }
};

export class JsonTrue extends JsonValue {
  constructor() { super(true, nodeTypes.TRUE); };
};

export class JsonFalse extends JsonValue {
  constructor() { super(false, nodeTypes.FALSE); };
};

export class JsonNull extends JsonValue {
  constructor() { super(null, nodeTypes.NULL); };
};

const nodeTypeObjectMapping = {
  [nodeTypes.DOCUMENT] : JsonDocument,
  [nodeTypes.COMMENT] : JsonComment,
  [nodeTypes.OBJECT] : JsonObject,
  [nodeTypes.PROPERTY] : JsonProperty,
  [nodeTypes.KEY] : JsonKey,
  [nodeTypes.ARRAY] : JsonArray,
  [nodeTypes.VALUE] : JsonValue,
  [nodeTypes.STRING] : JsonString,
  [nodeTypes.NUMBER] : JsonNumber,
  [nodeTypes.TRUE] : JsonTrue,
  [nodeTypes.FALSE] : JsonFalse,
  [nodeTypes.NULL] : JsonNull
};

//
// Utility methods to construct the objects
//
export class NodeFactory {
  constructor() {}

  static fromType(objectType, _value = null) {
    let clazz = nodeTypeObjectMapping[objectType];
    if (clazz === null)
      throw new Error(`AST node of type ${objectType} cannot be found`);
    return _value !== null ? new clazz(_value) : new clazz();
  }
}

function toJSON(jsonNode) {
  if (!(jsonNode instanceof JsonNode))
    throw new Error('JSON conversion only accepts a kind of JsonNode');

  // Just a recursive, slow implementation to a JavaScript object from this
  // JsonNode
  function recursiveNodeConversion(rootNode, parentObject) {
    let result = null;
    switch (rootNode.type) {
    case nodeTypes.DOCUMENT:
      return recursiveNodeConversion(rootNode.child);
    case nodeTypes.OBJECT: {
      result = {};
      rootNode.properties.forEach((propNode) => {
        result[recursiveNodeConversion(propNode.key)] =
            recursiveNodeConversion(propNode.value);
      });
      return result;
    }
    case nodeTypes.ARRAY: {
      result = [];
      rootNode.items.forEach(
          (itemNode) => { result.push(recursiveNodeConversion(itemNode)); });
      return result;
    }
    case nodeTypes.VALUE:
    case nodeTypes.STRING:
    case nodeTypes.KEY:
      return rootNode.value;
    case nodeTypes.NUMBER: {
      // typecast
      if (rootNode.value instanceof Number)
        return rootNode.value;
      return (new Number(rootNode.value)).valueOf();
    }
    case nodeTypes.TRUE:
      return true;
    case nodeTypes.FALSE:
      return false;
    case nodeTypes.NULL:
      return null;
    default:
      return undefined;
    }
  }

  return recursiveNodeConversion(jsonNode);
}