from sly import Lexer, Parser
import pprint

"""
Implementation with SLY of a very simple JSON parser.
Little reminder: here's the grammar

    json := object | array
    object := '{' members '}'
    members := pair | pair ',' members
    array := '[' elements ']'
    elements := value | value "," elements
    pair := STRING ':' value
    value := STRING | INTEGER | FLOAT | object | array

"""


class JsonLexer(Lexer):
    tokens = {STRING, NUMBER, TRUE, FALSE, NULL}
    ignore = ' \t\n\r'
    literals = {'{', '}', '[', ']', ':', ','}

    @_(r'-?(0|[1-9][0-9]*)(\.[0-9]+)?([Ee][+-]?[0-9]+)?')
    def NUMBER(self, t):
        t.value = float(t.value)
        return t

    @_(r'"([ !#-\[\]-\U0010ffff]+|\\(["\/\\bfnrt]|u[0-9A-Fa-f]{4}))*"')
    def STRING(self, t):
        t.value = json_unescape(t.value)
        return t

    @_(r'true')
    def TRUE(self, t):
        t.value = True
        return t

    @_(r'false')
    def FALSE(self, t):
        t.value = False
        return t

    @_(r'null')
    def NULL(self, t):
        t.value = None
        return t


class JsonParser(Parser):
    tokens = JsonLexer.tokens
    start = 'value'

    @_(r'"{" [ pairs ] "}"')
    def value(self, p):
        if p.pairs:
            return dict(p.pairs)
        else:
            return {}

    @_(r'pair { "," pair }')
    def pairs(self, p):
        return [p.pair0] + p.pair1

    @_(r'STRING ":" value')
    def pair(self, p):
        return (p.STRING, p.value)

    @_(r'"[" [ items ] "]"')
    def value(self, p):
        if p.items:
            return p.items
        else:
            return []

    @_(r'value { "," value }')
    def items(self, p):
        return [p.value0] + p.value1

    @_('STRING',
       'NUMBER',
       'TRUE',
       'FALSE',
       'NULL')
    def value(self, p):
        return p[0]

    def error(self, p):
        raise ValueError("Parsing error at token %s" % str(p))


if __name__ == "__main__":
    lexer = JSONLexer()
    parser = JSONParser()
    json_text = """{"menu": {
          "id": "file",
          "value": "File",
          "popup": {
            "menuitem": [
              {"value": "New", "onclick": "CreateNewDoc()"},
              {"value": "Open", "onclick": "OpenDoc()"},
              {"value": "Close", "onclick": "CloseDoc()"}
            ],
            "delay" : 1.5
          }
        }}
        """
    result = parser.parse(lexer.tokenize(json_text))
    pprint.pprint(result)