class Parser():
    def __init__(self, tokens):
        self.tokens = tokens
        self.i = 0
        self.t = None

    def peek(self):
        if self.end():
            return None
        self.t = self.tokens[self.i]
        return self.t

    def advance(self):
        self.i += 1
        return self.peek()

    def end(self):
        return self.i >= len(self.tokens)

    def parse(self):
        self.peek()
        if self.t['type'] == '{':
            result = self.parseObject()
        else:
            self.error('JSON Must start with brace `{`')

        return result

    def parseObject(self):
        self.advance()
        pairs = []
        first = True

        while not self.end():
            if self.t['type'] == '}':
                break
            if first:
                first = False
            elif self.t['type'] == ',':
                self.advance()
            if self.t['type'] == '}':
                break

            pairs.append(self.parsePair())


        self.advance()

        return pairs

    def parsePair(self):
        if self.t['type'] != 'str':
            self.error('Key must be type of string')

        key = self.t['val']
        val = ''
        tp = 'val'
        dataType = 'none'

        self.advance()

        if self.t['type'] != ':':
            self.error('Expected colon `:`')

        self.advance()

        if self.t['type'] in [ 'str', 'num', 'kw' ]:
            val = self.t['val']
            if self.t['type'] == 'str':
                dataType = 'string'
            elif self.t['type'] == 'kw' and self.t['val'] in [ 'false', 'true' ]:
                dataType = 'bool'
            elif self.t['type'] == 'num':
                dataType = 'double' if '.' in self.t['type'] else 'int'
            elif self.t['type'] == 'kw' and self.t['val'] == 'null':
                dataType = 'null'
            else:
                self.error('Unexpected type of token ' + self.t['type'])
        elif self.t['type'] == '{':
            val = self.parseObject()
            tp = 'obj'
        else:
            self.error('Unexpected type of token ' + self.t['type'])

        self.advance()

        return {
            "key": key,
            "val": val,
            "type": tp,
            "dataType": dataType
        }

    def error(self, message):
        raise Exception('[PARSER][ERROR] ' + message)