#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Example on how to write a JSON parser.

@author: lbo
"""

from pcombinators.combinators import *
from pcombinators.primitives import *

JString = Last(Skip(String('"')) + NoneInSet('"') + Skip(String('"')))

example_json = '{"id":1,"name":"Foo","price":123,"tags":["Bar","Eek"],"stock":{"warehouse":300,"retail":20}}'

class Value(Parser):
    """Bare-bones, but fully functioning, JSON parser. Doesn't like escaped quotes.

    Example:
        >>> Value().parse(ParseState(my_json_string))
        ({'id': 1.0,
          'name': 'Foo',
          'price': 123.0,
          'tags': ['Bar', 'Eek'],
          'stock': {'warehouse': 300.0, 'retail': 20.0}},
         ParseState({"id":1,"name":"Foo","price":123,"tags":["Bar","Eek"],"stock":{"warehouse":300,"retail":20}}<>))
    """
    def parse(self, st):
        return (Dict | List | JString | Float()).parse(st)

# We moved out all the piece parsers out of functions to reduce allocation overhead.
# It improves performance by roughly 2x.

# LISTS

def concat_elems_elem(l):
    if len(l) == 1:
        return l
    elif len(l) == 2 and type(l[0]) is list:
        l[0].append(l[1])
        return l[0]
    assert False, "Unexpected list format: {}".format(l)

# An entry is any value.
entry = Last(Value() + Skip(String(',') | Nothing()))
# A list is a [, followed by mid entries, followed by a final entry, and a
# closing ]. The list is wrapped in a list to prevent merging in other parsers.
# Flatten() takes care that the list from Repeat() and the single entry are made
# into one list.
List = Last(Skip(String('[')) +
        Repeat(entry, -1) +
        Skip(String(']')))

# DICTS

# A separator is whitespace, a colon, and more whitespace (Whitespace() also accepts empty string)
separator = Skip(String(":"))
# Entry is a String followed by a separator and a value. Wrap the value in a list to prevent merging.
# The two-element list is converted to a tuple.
entry = JString + separator + (Value()) >> (lambda l: tuple(l))
# A mid entry is followed by a comma.
midentry = Last(entry + Skip(String(',') | Nothing()))
# A dict is a {, followed by entries, followed by a final entry, followed by a closing }
dct = Flatten(
        Skip(String("{")) + Repeat(midentry, -1) + Skip(String("}")))
# Convert the list of tuples into a dict.
Dict = dct >> dict

def remove_unused_whitespace(s):
    acc = []
    lvl = 0
    ws = set(' \n\t\r')
    for c in s:
        if c == '"':
            lvl += 1 if lvl == 0 else -1
        if lvl == 0 and c in ws:
            continue
        acc.append(c)
    return ''.join(acc)

def parse_json(json):
    return Value().parse(ParseState(remove_unused_whitespace(json)))