jsonparser.ana

class AstNode {
  function AstNode(kind) {
    self.kind = kind;
    self.children = [];
  }
}

class Buffer
{
  function Buffer(value)
  {
    self.stream   = value;
    self.position = 0;
  }

  function advance()
  {
    if(self.position == self.stream.length())
    {
      throw "Can't advance buffer. Unexpected EOF";
    }

    return stream[self.position++];
  }

  function top()
  {
    return stream[self.position];
  }
}

function parse_int(buffer)
{
  val = 0;

  while(buffer.top() >= '0' && buffer.top() <= '9')
  {
    val = val * 10 + (int(buffer.top()) - int('0'));

    buffer.advance();
  }

  return val;
}

function parse_str(buffer)
{
  val = '';

  while(buffer.top() != '"')
  {
    val += buffer.top();

    buffer.advance();
  }

  buffer.advance();

  return val;
}

function is_int(val)
{
  return val >= '0' && val <= '9';
}

function is_string(val)
{
  return val == '"';
}

function skip_white(buffer)
{
  while(buffer.top() == ' ' || buffer.top() == '\t')
  {
    buffer.advance();
  }
}

function parse_key(buffer)
{
  skip_white(buffer);

  if(buffer.top() != '"')
  {
    throw 'Expected \'"\', not \'' + buffer.top() + '\' to start a key value pair at position ' + buffer.position;
  }

  key = '';
  buffer.advance();

  while(buffer.top() != '"')
  {
    key = key + buffer.top();

    buffer.advance();
  }

  if(buffer.top() != '"')
  {
    throw "Unexpected end of string literal, missing \"";
  }

  buffer.advance();

  return key;
}

class KeyValuePair
{
  function KeyValuePair(key, value)
  {
    self.key = key;
    self.value = value;
  }
}

function parse_object(buffer)
{ 
  node = AstNode("object");

  if(buffer.top() != '{')
  {
    throw "Expected '{' at position " + buffer.position;
  }

  buffer.advance();

  while(buffer.top() != '}')
  { 
    key = parse_key(buffer);

    skip_white(buffer);

    if(buffer.top() != ':')
    {
      throw "Expected ':' after key";
    }

    buffer.advance();

    skip_white(buffer);

    value = parse(buffer);

    node.children.push(KeyValuePair(key, value));

    buffer.advance();
  }

  return node;
}

function parse(buffer)
{
  if(buffer.top() == '{')
  {
    return parse_object(buffer);
  }
  else if(is_int(buffer.top()))
  {
    return parse_int(buffer);
  }
  else if(is_string(buffer.top()))
  {
    buffer.advance();
    return parse_str(buffer);
  }
  else
  {
    throw "Invalid start of JSON object at position " + buffer.position + ", got '" + buffer.top() + "'";
  }
}

function main()
{
  buffer = '';

  while(line = readline())
  {
    buffer = buffer + line;
  }

  buffer = Buffer(buffer);

  result = parse(buffer);

  foreach(kvpair in result.children)
  {
    print(kvpair.key + ":" + kvpair.value);
  }
}

main();