| 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 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._get_all_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 | users = self._get_users_by_names(user_names) |
| 34 | return json.dumps({"users": users}) |
| 35 | |
| 36 | # Edge Case: Invalid URL |
| 37 | return json.dumps({"error": "Invalid URL"}) |
| 38 | |
| 8 | 39 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 40 | """ |
| 41 | Handle POST requests to the API. |
| 42 | |
| 43 | Args: |
| 44 | url: The endpoint URL. |
| 45 | payload: Optional JSON payload. |
| 46 | |
| 47 | Returns: |
| 48 | A JSON string response. |
| 49 | """ |
| 50 | if payload is None: |
| 51 | # Edge Case: Missing payload |
| 52 | return json.dumps({"error": "Payload required"}) |
| 53 | |
| 54 | data = json.loads(payload) |
| 55 | |
| 56 | if url == "/add": |
| 57 | user_name = data.get("user") |
| 58 | |
| 59 | # Edge Case: Missing user name |
| 60 | if not user_name: |
| 61 | return json.dumps({"error": "User name required"}) |
| 62 | |
| 63 | # If user already exists, return the existing user |
| 64 | if self._user_exists(user_name): |
| 65 | existing_user = self._get_user_by_name(user_name) |
| 66 | user_copy = existing_user.copy() |
| 67 | user_copy["balance"] = self._calculate_balance(existing_user) |
| 68 | return json.dumps(user_copy) |
| 69 | |
| 70 | new_user = self._create_user(user_name) |
| 71 | self.database["users"].append(new_user) |
| 72 | # Add balance to the returned user object |
| 73 | new_user_copy = new_user.copy() |
| 74 | new_user_copy["balance"] = 0.0 |
| 75 | return json.dumps(new_user_copy) |
| 76 | |
| 77 | elif url == "/iou": |
| 78 | lender_name = data.get("lender") |
| 79 | borrower_name = data.get("borrower") |
| 80 | amount = data.get("amount") |
| 81 | |
| 82 | # Edge Case: Missing required fields |
| 83 | if not lender_name or not borrower_name or amount is None: |
| 84 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 85 | |
| 86 | # Edge Case: Lender and borrower are the same |
| 87 | if lender_name == borrower_name: |
| 88 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 89 | |
| 90 | # Edge Case: Negative amount |
| 91 | if amount < 0: |
| 92 | return json.dumps({"error": "Amount must be positive"}) |
| 93 | |
| 94 | # Edge Case: User does not exist |
| 95 | if not self._user_exists(lender_name) or not self._user_exists(borrower_name): |
| 96 | return json.dumps({"error": "User does not exist"}) |
| 97 | |
| 98 | # Update IOUs |
| 99 | self._update_iou(lender_name, borrower_name, amount) |
| 100 | |
| 101 | # Return updated users with recalculated balances |
| 102 | lender = self._get_user_by_name(lender_name) |
| 103 | borrower = self._get_user_by_name(borrower_name) |
| 104 | |
| 105 | # Create copies with updated balances |
| 106 | lender_copy = lender.copy() |
| 107 | lender_copy["balance"] = self._calculate_balance(lender) |
| 108 | borrower_copy = borrower.copy() |
| 109 | borrower_copy["balance"] = self._calculate_balance(borrower) |
| 110 | |
| 111 | users = sorted([lender_copy, borrower_copy], key=lambda x: x["name"]) |
| 112 | return json.dumps({"users": users}) |
| 113 | |
| 114 | # Edge Case: Invalid URL |
| 115 | return json.dumps({"error": "Invalid URL"}) |
| 116 | |
| 117 | def _get_all_users(self) -> list: |
| 118 | """ |
| 119 | Get all users from the database with calculated balances. |
| 120 | |
| 121 | Returns: |
| 122 | A list of user objects with calculated balances. |
| 123 | """ |
| 124 | users = [] |
| 125 | for user in self.database["users"]: |
| 126 | user_copy = user.copy() |
| 127 | user_copy["balance"] = self._calculate_balance(user) |
| 128 | users.append(user_copy) |
| 129 | return sorted(users, key=lambda x: x["name"]) |
| 130 | |
| 131 | |
| 132 | def _get_users_by_names(self, names: list) -> list: |
| 133 | """ |
| 134 | Get specific users by their names. |
| 135 | |
| 136 | Args: |
| 137 | names: A list of user names. |
| 138 | |
| 139 | Returns: |
| 140 | A list of user objects with calculated balances, sorted by name. |
| 141 | """ |
| 142 | users = [] |
| 143 | for name in names: |
| 144 | user = self._get_user_by_name(name) |
| 145 | if user: |
| 146 | user_copy = user.copy() |
| 147 | user_copy["balance"] = self._calculate_balance(user) |
| 148 | users.append(user_copy) |
| 149 | return sorted(users, key=lambda x: x["name"]) |
| 150 | |
| 151 | def _get_user_by_name(self, name: str) -> dict | None: |
| 152 | """ |
| 153 | Get a user by their name. |
| 154 | |
| 155 | Args: |
| 156 | name: The name of the user. |
| 157 | |
| 158 | Returns: |
| 159 | The user object or None if not found. |
| 160 | """ |
| 161 | for user in self.database["users"]: |
| 162 | if user["name"] == name: |
| 163 | return user |
| 164 | return None |
| 165 | |
| 166 | def _user_exists(self, name: str) -> bool: |
| 167 | """ |
| 168 | Check if a user exists in the database. |
| 169 | |
| 170 | Args: |
| 171 | name: The name of the user. |
| 172 | |
| 173 | Returns: |
| 174 | True if the user exists, False otherwise. |
| 175 | """ |
| 176 | return self._get_user_by_name(name) is not None |
| 177 | |
| 178 | def _create_user(self, name: str) -> dict: |
| 179 | """ |
| 180 | Create a new user object. |
| 181 | |
| 182 | Args: |
| 183 | name: The name of the user. |
| 184 | |
| 185 | Returns: |
| 186 | A new user object. |
| 187 | """ |
| 188 | return { |
| 189 | "name": name, |
| 190 | "owes": {}, |
| 191 | "owed_by": {} |
| 192 | } |
| 193 | |
| 194 | def _calculate_balance(self, user: dict) -> float: |
| 195 | """ |
| 196 | Calculate the balance for a user. |
| 197 | |
| 198 | Args: |
| 199 | user: The user object. |
| 200 | |
| 201 | Returns: |
| 202 | The calculated balance. |
| 203 | """ |
| 204 | total_owed_by = sum(user["owed_by"].values()) |
| 205 | total_owes = sum(user["owes"].values()) |
| 206 | return round(total_owed_by - total_owes, 2) |
| 207 | |
| 208 | def _update_iou(self, lender_name: str, borrower_name: str, amount: float) -> None: |
| 209 | """ |
| 210 | Update the IOU records between lender and borrower. |
| 211 | |
| 212 | Args: |
| 213 | lender_name: The name of the lender. |
| 214 | borrower_name: The name of the borrower. |
| 215 | amount: The amount of the IOU. |
| 216 | """ |
| 217 | lender = self._get_user_by_name(lender_name) |
| 218 | borrower = self._get_user_by_name(borrower_name) |
| 219 | |
| 220 | # Check if lender already owes borrower (opposite debt) |
| 221 | lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 222 | # Check if borrower already owes lender |
| 223 | borrower_owes_lender = borrower["owes"].get(lender_name, 0) |
| 224 | |
| 225 | if lender_owes_borrower > 0: |
| 226 | # Lender already owes borrower - net the debts |
| 227 | if amount > lender_owes_borrower: |
| 228 | # New IOU is larger than existing debt - cancel debt and create reverse |
| 229 | remaining_amount = round(amount - lender_owes_borrower, 2) |
| 230 | del lender["owes"][borrower_name] |
| 231 | del borrower["owed_by"][lender_name] |
| 232 | |
| 233 | # Create new debt in reverse direction |
| 234 | lender["owed_by"][borrower_name] = remaining_amount |
| 235 | borrower["owes"][lender_name] = remaining_amount |
| 236 | elif amount == lender_owes_borrower: |
| 237 | # Debts exactly cancel out |
| 238 | del lender["owes"][borrower_name] |
| 239 | del borrower["owed_by"][lender_name] |
| 240 | else: |
| 241 | # New IOU is smaller than existing debt - reduce the existing debt |
| 242 | new_debt = round(lender_owes_borrower - amount, 2) |
| 243 | lender["owes"][borrower_name] = new_debt |
| 244 | borrower["owed_by"][lender_name] = new_debt |
| 245 | elif borrower_owes_lender > 0: |
| 246 | # Borrower already owes lender - create new debt relationship in opposite direction |
| 247 | # This maintains both debt relationships rather than netting them |
| 248 | lender["owes"][borrower_name] = amount |
| 249 | borrower["owed_by"][lender_name] = amount |
| 250 | else: |
| 251 | # No existing debts - create new debt |
| 252 | # Update lender's owed_by (who owes them money) |
| 253 | if borrower_name in lender["owed_by"]: |
| 254 | lender["owed_by"][borrower_name] = round(lender["owed_by"][borrower_name] + amount, 2) |
| 255 | else: |
| 256 | lender["owed_by"][borrower_name] = amount |
| 257 | |
| 258 | # Update borrower's owes (who they owe money to) |
| 259 | if lender_name in borrower["owes"]: |
| 260 | borrower["owes"][lender_name] = round(borrower["owes"][lender_name] + amount, 2) |
| 261 | else: |
| 262 | borrower["owes"][lender_name] = amount |
| 263 | |
| 264 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Lender and borrower are the same, Negative amount, User does not exist |