| 1 | import json |
| 2 | |
| 1 | 3 | class RestAPI: |
| 2 | 4 | def __init__(self, database: dict | None = None): |
| 3 | | pass |
| 4 | | |
| 5 | """ |
| 6 | Initialize the REST API with a database. |
| 7 | |
| 8 | Args: |
| 9 | database: A dictionary containing user data. |
| 10 | """ |
| 11 | self.database = database if database is not None else {"users": []} |
| 12 | |
| 5 | 13 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 14 | """ |
| 15 | Handle GET requests to the API. |
| 16 | |
| 17 | Args: |
| 18 | url: The endpoint URL. |
| 19 | payload: Optional JSON payload. |
| 20 | |
| 21 | Returns: |
| 22 | A JSON string response. |
| 23 | """ |
| 24 | if url == "/users": |
| 25 | if payload is None: |
| 26 | # Return all users |
| 27 | users = [self._create_user_object(user) for user in self.database["users"]] |
| 28 | return json.dumps({"users": users}) |
| 29 | else: |
| 30 | # Return specific users |
| 31 | data = json.loads(payload) |
| 32 | user_names = data.get("users", []) |
| 33 | |
| 34 | # Edge Case: Empty user list in payload |
| 35 | if not user_names: |
| 36 | return json.dumps({"users": []}) |
| 37 | |
| 38 | # Edge Case: Non-existent users in payload |
| 39 | users = [] |
| 40 | for user_name in user_names: |
| 41 | user = self._find_user(user_name) |
| 42 | if user is not None: |
| 43 | users.append(self._create_user_object(user)) |
| 44 | |
| 45 | # Sort users by name |
| 46 | users.sort(key=lambda u: u["name"]) |
| 47 | return json.dumps({"users": users}) |
| 48 | |
| 49 | # Edge Case: Invalid URL |
| 50 | return json.dumps({"error": "Invalid URL"}) |
| 51 | |
| 8 | 52 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 53 | """ |
| 54 | Handle POST requests to the API. |
| 55 | |
| 56 | Args: |
| 57 | url: The endpoint URL. |
| 58 | payload: JSON payload. |
| 59 | |
| 60 | Returns: |
| 61 | A JSON string response. |
| 62 | """ |
| 63 | if payload is None: |
| 64 | # Edge Case: Missing payload |
| 65 | return json.dumps({"error": "Payload required"}) |
| 66 | |
| 67 | data = json.loads(payload) |
| 68 | |
| 69 | if url == "/add": |
| 70 | user_name = data.get("user") |
| 71 | |
| 72 | # Edge Case: Missing user name |
| 73 | if user_name is None: |
| 74 | return json.dumps({"error": "User name required"}) |
| 75 | |
| 76 | # Edge Case: User already exists - return existing user |
| 77 | existing_user = self._find_user(user_name) |
| 78 | if existing_user is not None: |
| 79 | return json.dumps(self._create_user_object(existing_user)) |
| 80 | |
| 81 | new_user = { |
| 82 | "name": user_name, |
| 83 | "owes": {}, |
| 84 | "owed_by": {}, |
| 85 | "balance": 0.0 |
| 86 | } |
| 87 | self.database["users"].append(new_user) |
| 88 | return json.dumps(self._create_user_object(new_user)) |
| 89 | |
| 90 | elif url == "/iou": |
| 91 | lender_name = data.get("lender") |
| 92 | borrower_name = data.get("borrower") |
| 93 | amount = data.get("amount") |
| 94 | |
| 95 | # Edge Case: Missing required fields |
| 96 | if lender_name is None or borrower_name is None or amount is None: |
| 97 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 98 | |
| 99 | # Edge Case: Lender and borrower are the same |
| 100 | if lender_name == borrower_name: |
| 101 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 102 | |
| 103 | lender = self._find_user(lender_name) |
| 104 | borrower = self._find_user(borrower_name) |
| 105 | |
| 106 | # Edge Case: Non-existent lender or borrower |
| 107 | if lender is None or borrower is None: |
| 108 | return json.dumps({"error": "Lender or borrower does not exist"}) |
| 109 | |
| 110 | # Handle the IOU transaction by updating both sides properly |
| 111 | # First, check if there's an existing debt in the opposite direction |
| 112 | if borrower_name in lender["owes"]: |
| 113 | # Lender already owes borrower - reduce that debt first |
| 114 | existing_debt = lender["owes"][borrower_name] |
| 115 | if existing_debt > amount: |
| 116 | # Reduce the existing debt |
| 117 | lender["owes"][borrower_name] = existing_debt - amount |
| 118 | borrower["owed_by"][lender_name] = existing_debt - amount |
| 119 | # No new debt created, just reduce existing |
| 120 | lender["balance"] += amount |
| 121 | borrower["balance"] -= amount |
| 122 | elif existing_debt == amount: |
| 123 | # Exact match - remove the debt entries |
| 124 | del lender["owes"][borrower_name] |
| 125 | del borrower["owed_by"][lender_name] |
| 126 | lender["balance"] += amount |
| 127 | borrower["balance"] -= amount |
| 128 | else: |
| 129 | # Existing debt is less than new amount - remove debt and create new one |
| 130 | del lender["owes"][borrower_name] |
| 131 | del borrower["owed_by"][lender_name] |
| 132 | new_debt = amount - existing_debt |
| 133 | lender["owed_by"][borrower_name] = new_debt |
| 134 | borrower["owes"][lender_name] = new_debt |
| 135 | lender["balance"] += amount |
| 136 | borrower["balance"] -= amount |
| 137 | elif borrower_name in lender["owed_by"]: |
| 138 | # There's already a debt in this direction - add to it |
| 139 | lender["owed_by"][borrower_name] += amount |
| 140 | borrower["owes"][lender_name] += amount |
| 141 | lender["balance"] += amount |
| 142 | borrower["balance"] -= amount |
| 143 | else: |
| 144 | # No existing debt - create new one |
| 145 | lender["owed_by"][borrower_name] = amount |
| 146 | borrower["owes"][lender_name] = amount |
| 147 | lender["balance"] += amount |
| 148 | borrower["balance"] -= amount |
| 149 | |
| 150 | # Return updated user objects |
| 151 | users = [ |
| 152 | self._create_user_object(lender), |
| 153 | self._create_user_object(borrower) |
| 154 | ] |
| 155 | users.sort(key=lambda u: u["name"]) |
| 156 | return json.dumps({"users": users}) |
| 157 | |
| 158 | # Edge Case: Invalid URL |
| 159 | return json.dumps({"error": "Invalid URL"}) |
| 160 | |
| 161 | def _find_user(self, name: str): |
| 162 | """ |
| 163 | Find a user by name in the database. |
| 164 | |
| 165 | Args: |
| 166 | name: The name of the user to find. |
| 167 | |
| 168 | Returns: |
| 169 | The user object if found, None otherwise. |
| 170 | """ |
| 171 | for user in self.database["users"]: |
| 172 | if user["name"] == name: |
| 173 | return user |
| 174 | return None |
| 175 | |
| 176 | def _create_user_object(self, user): |
| 177 | """ |
| 178 | Create a user object for API response. |
| 179 | |
| 180 | Args: |
| 181 | user: The user data from the database. |
| 182 | |
| 183 | Returns: |
| 184 | A dictionary representing the user object. |
| 185 | """ |
| 186 | return { |
| 187 | "name": user["name"], |
| 188 | "owes": user["owes"], |
| 189 | "owed_by": user["owed_by"], |
| 190 | "balance": round(user["balance"], 2) |
| 191 | } |
| 192 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Lender and borrower are the same, Non-existent lender or borrower, Empty user list in payload, Non-existent users in payload |