import uuid
import json
import os.path

class Collection:
    def __init__(self, name, db_name):
        self.name = name
        self.db_name = db_name
        self.data = {}
        filename = db_name + '_' + name
        if (os.path.isfile(filename)):
            datafile = open(filename, "r")
            loaded = json.loads(datafile.read())
            self.data = loaded

    def __getitem__(self, key):
        return self.data[key]

    def __delitem__(self, key):
        del self.data[key]

    def insert(self, dict):
        uid = str(uuid.uuid4())
        self.data[uid] = dict
        self.save()
        return uid

    def find(self, dict):
        results = []
        for key in self.data:
            if(all(item in self.data[key].items() for item in dict.items())):
                results.append(self.data[key])
        return results

    def save(self):
        text = json.dumps(self.data)
        text_file = open(self.db_name + '_' + self.name, "w")
        text_file.write(text)
        text_file.close()

class DB:
    def __init__(self, name):
        self.name = name
        self.data = {}

    def __getattr__(self, attr):
        if (not(attr in self.__dict__)):
            self.data[attr] = Collection(attr, self.name)
        return self.data[attr]

    def __enter__(self):
        return self

    def __exit__(self, type, value, traceback):
        pass

# Test

with DB('db name') as db:
 collection = db.my_product_collection # collection is an instance of Collection
 # 'my_product_collection' can be any string identifying this specific collection
 # One DB has multiple Collections. One Collection has multiple documents
 uid = collection.insert({'my': 'val'}) # insert always get a dict as its sole argument
 print(collection[uid])
 del collection[uid]
 collection.insert({'name': 'Bob', 'group': 'A', 'age': 22})
 collection.insert({'name': 'Alice', 'group': 'A', 'age': 22})
 collection.insert({'name': 'John', 'group': 'B'})
 collection.insert({'name': 'Jack', 'email': 'jack@domain.tld'})
 for uid, it in collection.find({'group': 'A', 'age': 22}):
 # Equivalent to 'SELECT * FROM my_product_collection WHERE group == "A" AND age == 22'
 # Find always receives a dict, the query, and should return all the documents
 # that have all the keys in the query with the right value
 # Here: Bob and Alice
    print('found', uid, it)