# coding:utf-8
import operator

ops = (
    'lt',
    'lte',
    'gt',
    'gte',
)


class Table:
    def __init__(self, name, schema, rows=None):
        self.name = name
        self.schema = schema
        self.rows = rows or []


class Query:
    def __init__(self, table):
        self.tables = [table]
        self.filters = []

    def select(self, *columns):
        ci = [self.column_index(c) for c in columns]
        for row in self._rows():
            yield tuple(row[i] for i in ci)

    def select_all(self):
        return self._filter()

    def _rows(self):
        return self.tables[0].rows

    def column_index(self, name):
        return self.tables[0].schema.index(name)

    def _filter(self):
        def _rows(filter_, column, rows):
            ci = self.column_index(column)
            for row in rows:
                if filter_(row[ci]):
                    yield row

        rows = self._rows()
        for filter_, column in self.filters:
            rows = _rows(filter_, column, rows)
        return rows

    def where(self, **kwargs):
        for column, value in kwargs.items():
            self._where(column, value)
        return self

    def _where(self, column, value):
        def make_filter(predicate, value):
            def _filter(x):
                if x is not None and predicate(x, value):
                    return True
                return False
            return _filter

        tmp = column.rsplit('__', 1)
        if len(tmp) == 2:
            column, op = tmp
            if op not in ops:
                raise ValueError('Invalid operator: %s' % op)
            predicate = getattr(operator, op)
        else:
            predicate = operator.eq
        filter_ = make_filter(predicate, value)
        self.filters.append((filter_, column))


def print_list(l):
    print(list(l))


Items = Table(
    'items',
    ('id', 'name', 'category', 'price'),
    [
        (1, "りんご", 1, 300),
        (2, "みかん", 1, 130),
        (3, "キャベツ", 2, 200),
        (4, "わかめ", None, 250),
        (5, "しいたけ", 3, 180),
    ],
)

print_list(Query(Items).select_all())
print_list(Query(Items).where(id__gt=1, category=2).select_all())
print_list(Query(Items).select('id', 'name'))
print_list(Query(Items).where(category__gt=1).select_all())