Rest API exercise

python/rest-api/.exercism/metadata.json

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+{"track":"python","exercise":"rest-api","id":"1c88ea7c565c4133a44bcc020617803d","url":"https://exercism.io/my/solutions/1c88ea7c565c4133a44bcc020617803d","handle":"Xevion","is_requester":true,"auto_approve":false}

python/rest-api/README.md

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+# Rest Api
+
+Implement a RESTful API for tracking IOUs.
+
+Four roommates have a habit of borrowing money from each other frequently, and have trouble remembering who owes whom, and how much.
+
+Your task is to implement a simple [RESTful API](https://en.wikipedia.org/wiki/Representational_state_transfer) that receives [IOU](https://en.wikipedia.org/wiki/IOU)s as POST requests, and can deliver specified summary information via GET requests.
+
+### API Specification
+
+#### User object
+```json
+{
+  "name": "Adam",
+  "owes": {
+    "Bob": 12.0,
+    "Chuck": 4.0,
+    "Dan": 9.5
+  },
+  "owed_by": {
+    "Bob": 6.5,
+    "Dan": 2.75,
+  },
+  "balance": "<(total owed by other users) - (total owed to other users)>"
+}
+```
+
+#### Methods
+
+| Description | HTTP Method | URL | Payload Format | Response w/o Payload | Response w/ Payload |
+| --- | --- | --- | --- | --- | --- |
+| List of user information | GET | /users | `{"users":["Adam","Bob"]}` | `{"users":<List of all User objects>}` | `{"users":<List of User objects for <users> (sorted by name)}` |
+| Create user | POST | /add | `{"user":<name of new user (unique)>}` | N/A | `<User object for new user>` |
+| Create IOU | POST | /iou | `{"lender":<name of lender>,"borrower":<name of borrower>,"amount":5.25}` | N/A | `{"users":<updated User objects for <lender> and <borrower> (sorted by name)>}` |
+
+### Other Resources:
+- https://restfulapi.net/
+- Example RESTful APIs
+  - [GitHub](https://developer.github.com/v3/)
+  - [Reddit](https://www.reddit.com/dev/api/)
+## Exception messages
+
+Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to
+indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not
+every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include
+a message.
+
+To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
+`raise Exception`, you should write:
+
+```python
+raise Exception("Meaningful message indicating the source of the error")
+```
+
+## Running the tests
+
+To run the tests, run the appropriate command below ([why they are different](https://github.com/pytest-dev/pytest/issues/1629#issue-161422224)):
+
+- Python 2.7: `py.test rest_api_test.py`
+- Python 3.4+: `pytest rest_api_test.py`
+
+Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
+`python -m pytest rest_api_test.py`
+
+### Common `pytest` options
+
+- `-v` : enable verbose output
+- `-x` : stop running tests on first failure
+- `--ff` : run failures from previous test before running other test cases
+
+For other options, see `python -m pytest -h`
+
+## Submitting Exercises
+
+Note that, when trying to submit an exercise, make sure the solution is in the `$EXERCISM_WORKSPACE/python/rest-api` directory.
+
+You can find your Exercism workspace by running `exercism debug` and looking for the line that starts with `Workspace`.
+
+For more detailed information about running tests, code style and linting,
+please see [Running the Tests](http://exercism.io/tracks/python/tests).
+
+## Submitting Incomplete Solutions
+
+It's possible to submit an incomplete solution so you can see how others have completed the exercise.

python/rest-api/rest_api.py

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+import json
+
+# Comments on this exercise:
+    # I honestly kind of hate this problem because you're forced to store the users in a array essentially...
+    # which means that users are not especially unique unless you add this functionality yourself, which is kind of hassle tbh.
+    # This could be solved if we just had a dictionary of users where the values were users themselves. Bam. Problem solved.
+    # This database is kind of useless because it's literally a dictionary with a single key, Users, which has a array, with the problem above.
+    # Super annoying implementation I have to work with, and sure, 100%, you could just rewrite everything to convert databases from and to, but it's a hassle none the less of
+    # converting and properly displaying databases with their conventions. >:(
+    # Addtionally, the optional payloads are annoying. 
+# Thoughts after solving:
+    # I have no idea if ValueErrors were tested in this exercise, but I implemented them anyways in order to catch them if they ever appeared,
+    # as after all, a large portion of the parameters that one could issue in this "Rest API" are optional to a point, and thus I assumed errors
+    # were most definitely possible.
+    # Not a bad exercise in the end, but it's annoying how this 'database' is implemented...
+
+class RestAPI(object):
+    def __init__(self, database=None):
+        self.database = database or {"users" : []}
+
+    def get(self, url, payload=None):
+        if url == '/users':
+            if not payload:
+                return json.dumps(self.database)
+            data = json.loads(payload)
+            return json.dumps({"users" : [user for user in self.database["users"] if user['name'] in data['users']]})
+        else:
+            raise ValueError(f'Invalid URL \'{url}\'')
+
+    def post(self, url, payload=None):
+        if not payload:
+            raise("No payload for URL \'{}\'".foramt(url))
+        elif url == '/add':
+            return self.add(payload) or json.dumps('?')
+        elif url == '/iou':
+            return self.iou(payload) or json.dumps('?')
+        else:
+            raise ValueError("Invalid URL \'{}\'".foramt(url))
+
+    def get_user(self, name):
+        found = [user for user in self.database['users'] if user['name'] == name]
+        if len(found) >= 1:
+            return found[0]
+        else:
+            raise ValueError('User \'{}\' does not exist.'.format(name))
+            return False
+
+    def set_user(self, name, data):
+        found = [(index, user) for index, user in enumerate(self.database['users']) if user['name'] == name]
+        if len(found) == 1:
+            print('User {} set'.format(name))
+            self.database['users'][found[0][0]] = data
+            print(self.database['users'][found[0][0]])
+        else:
+            raise ValueError('User \'{}\' does not exist.'.format(name))
+            return False
+
+    # Add a user to the database
+    def add(self, payload):
+        data = json.loads(payload)
+        if data['user'] in self.database.keys():
+            raise ValueError('User {} already exists.'.format(data['name']))
+        self.database['users'].append({'name' : data['user'], 'owes' : {}, 'owed_by' : {}, 'balance' : 0.0})
+        return json.dumps(self.get_user(data['user']))
+
+    def iou(self, payload):
+        data = json.loads(payload)
+        lender, borrower = self.get_user(data['lender']), self.get_user(data['borrower'])
+        
+        # if the lender owes the borrower money
+        if data['borrower'] in lender['owes'].keys():
+            dif = lender['owes'][data['borrower']] - data['amount']
+            # lender still owes borrower money
+            if dif > 0:
+                lender['owes'][data['borrower']] = dif
+                borrower['owed_by'][data['lender']] = dif
+            # all ious paid between lender and borrower now
+            elif dif == 0:
+                del lender['owes'][data['borrower']]
+                del borrower['owed_by'][data['lender']]
+            # lender is now owed money by borrower
+            elif dif < 0:
+                del lender['owes'][data['borrower']]
+                del borrower['owed_by'][data['lender']]
+                lender['owed_by'][data['borrower']] = -dif
+                borrower['owes'][data['lender']] = -dif
+
+        # if the borrower already owes the lender money
+        elif data['borrower'] in lender['owed_by'].keys():
+            lender['owed_by'][data['borrower']] += data['amount']
+            borrower['owes'][data['lender']] -= data['amount']
+
+        # if the borrower and lender have no outstanding ious
+        else:
+            lender['owed_by'][data['borrower']] = data['amount']
+            borrower['owes'][data['lender']] = data['amount']
+
+        # Balance operations
+        lender['balance'] += data['amount']
+        borrower['balance'] -= data['amount']
+
+        self.set_user(data['lender'], lender)
+        self.set_user(data['borrower'], borrower)
+
+        return json.dumps({"users" : [user for user in self.database["users"] if user['name'] in [data['lender'], data['borrower']]]})

python/rest-api/rest_api_test.py

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+import unittest
+import json
+
+from rest_api import RestAPI
+
+
+# Tests adapted from `problem-specifications//canonical-data.json` @ v1.1.1
+
+class RestAPITest(unittest.TestCase):
+    def test_no_users(self):
+        database = {"users": []}
+        api = RestAPI(database)
+        response = api.get('/users')
+        self.assertDictEqual(json.loads(response), database)
+
+    def test_add_user(self):
+        database = {"users": []}
+        api = RestAPI(database)
+        payload = json.dumps({
+            'user': 'Adam'
+        })
+        response = api.post('/add', payload)
+        expected = {
+            'name': 'Adam',
+            'owes': {},
+            'owed_by': {},
+            'balance': 0
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_get_single_user(self):
+        database = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'users': ['Bob']
+        })
+        response = api.get('/users', payload)
+        expected = {
+            'users': [
+                {
+                    'name': 'Bob',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_iou_both_users_have_0_balance(self):
+        database = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'lender': 'Adam',
+            'borrower': 'Bob',
+            'amount': 3
+        })
+        response = api.post('/iou', payload)
+        expected = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {},
+                    'owed_by': {
+                        'Bob': 3
+                    },
+                    'balance': 3
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {
+                        'Adam': 3
+                    },
+                    'owed_by': {},
+                    'balance': -3
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_borrower_has_negative_balance(self):
+        database = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {
+                        'Chuck': 3
+                    },
+                    'owed_by': {},
+                    'balance': -3
+                },
+                {
+                    'name': 'Chuck',
+                    'owes': {},
+                    'owed_by': {
+                        'Bob': 3
+                    },
+                    'balance': 3
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'lender': 'Adam',
+            'borrower': 'Bob',
+            'amount': 3
+        })
+        response = api.post('/iou', payload)
+        expected = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {},
+                    'owed_by': {
+                        'Bob': 3
+                    },
+                    'balance': 3
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {
+                        'Adam': 3,
+                        'Chuck': 3
+                    },
+                    'owed_by': {},
+                    'balance': -6
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_lender_has_negative_balance(self):
+        database = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {},
+                    'owed_by': {},
+                    'balance': 0
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {
+                        'Chuck': 3
+                    },
+                    'owed_by': {},
+                    'balance': -3
+                },
+                {
+                    'name': 'Chuck',
+                    'owes': {},
+                    'owed_by': {
+                        'Bob': 3
+                    },
+                    'balance': 3
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'lender': 'Bob',
+            'borrower': 'Adam',
+            'amount': 3
+        })
+        response = api.post('/iou', payload)
+        expected = {
+            'users': [
+                {
+                    'name': 'Adam',
+                    'owes': {
+                        'Bob': 3
+                    },
+                    'owed_by': {},
+                    'balance': -3
+                },
+                {
+                    'name': 'Bob',
+                    'owes': {
+                        'Chuck': 3
+                    },
+                    'owed_by': {
+                        'Adam': 3
+                    },
+                    'balance': 0
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_lender_owes_borrower(self):
+        database = {
+            "users": [
+                {
+                    "name": "Adam",
+                    "owes": {
+                        "Bob": 3.0
+                    },
+                    "owed_by": {},
+                    "balance": -3.0
+                },
+                {
+                    "name": "Bob",
+                    "owes": {},
+                    "owed_by": {
+                        "Adam": 3.0
+                    },
+                    "balance": 3.0
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'lender': 'Adam',
+            'borrower': 'Bob',
+            'amount': 2
+        })
+        response = api.post('/iou', payload)
+        expected = {
+            'users': [
+                {
+                    "name": "Adam",
+                    "owes": {
+                        "Bob": 1.0
+                    },
+                    "owed_by": {},
+                    "balance": -1.0
+                },
+                {
+                    "name": "Bob",
+                    "owes": {},
+                    "owed_by": {
+                        "Adam": 1.0
+                    },
+                    "balance": 1.0
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_lender_owes_borrower_less_than_new_loan(self):
+        database = {
+            "users": [
+                {
+                    "name": "Adam",
+                    "owes": {
+                        "Bob": 3.0
+                    },
+                    "owed_by": {},
+                    "balance": -3.0
+                },
+                {
+                    "name": "Bob",
+                    "owes": {},
+                    "owed_by": {
+                        "Adam": 3.0
+                    },
+                    "balance": 3.0
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'lender': 'Adam',
+            'borrower': 'Bob',
+            'amount': 4.0
+        })
+        response = api.post('/iou', payload)
+        expected = {
+            'users': [
+                {
+                    "name": "Adam",
+                    "owes": {
+                    },
+                    "owed_by": {
+                        "Bob": 1.0
+                    },
+                    "balance": 1.0
+                },
+                {
+                    "name": "Bob",
+                    "owes": {
+                        "Adam": 1.0
+                    },
+                    "owed_by": {
+                    },
+                    "balance": -1.0
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+    def test_lender_owes_borrower_same_as_new_loan(self):
+        database = {
+            "users": [
+                {
+                    "name": "Adam",
+                    "owes": {
+                        "Bob": 3.0
+                    },
+                    "owed_by": {},
+                    "balance": -3.0
+                },
+                {
+                    "name": "Bob",
+                    "owes": {},
+                    "owed_by": {
+                        "Adam": 3.0
+                    },
+                    "balance": 3.0
+                }
+            ]
+        }
+        api = RestAPI(database)
+        payload = json.dumps({
+            'lender': 'Adam',
+            'borrower': 'Bob',
+            'amount': 3.0
+        })
+        response = api.post('/iou', payload)
+        expected = {
+            'users': [
+                {
+                    "name": "Adam",
+                    "owes": {
+                    },
+                    "owed_by": {
+                    },
+                    "balance": 0.0
+                },
+                {
+                    "name": "Bob",
+                    "owes": {
+                    },
+                    "owed_by": {
+                    },
+                    "balance": 0.0
+                }
+            ]
+        }
+        self.assertDictEqual(json.loads(response), expected)
+
+
+if __name__ == '__main__':
+    unittest.main()