| 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 an optional database. |
| 7 | |
| 8 | Args: |
| 9 | database: A dictionary containing initial user data. |
| 10 | """ |
| 11 | if database is None: |
| 12 | self.database = {"users": []} |
| 13 | else: |
| 14 | self.database = database |
| 15 | |
| 5 | 16 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 17 | """ |
| 18 | Handle GET requests to the API. |
| 19 | |
| 20 | Args: |
| 21 | url: The endpoint URL. |
| 22 | payload: Optional JSON payload. |
| 23 | |
| 24 | Returns: |
| 25 | A JSON string response. |
| 26 | |
| 27 | Raises: |
| 28 | ValueError: If the URL is not recognized. |
| 29 | """ |
| 30 | if url == "/users": |
| 31 | if payload is None: |
| 32 | # Return all users |
| 33 | return json.dumps({"users": self._get_all_users()}) |
| 34 | else: |
| 35 | # Return specific users |
| 36 | data = json.loads(payload) |
| 37 | user_names = data.get("users", []) |
| 38 | return json.dumps({"users": self._get_users_by_names(user_names)}) |
| 39 | else: |
| 40 | raise ValueError(f"Unknown GET endpoint: {url}") |
| 41 | |
| 8 | 42 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 43 | """ |
| 44 | Handle POST requests to the API. |
| 45 | |
| 46 | Args: |
| 47 | url: The endpoint URL. |
| 48 | payload: JSON payload. |
| 49 | |
| 50 | Returns: |
| 51 | A JSON string response. |
| 52 | |
| 53 | Raises: |
| 54 | ValueError: If the URL is not recognized or if required data is missing. |
| 55 | """ |
| 56 | if url == "/add": |
| 57 | if payload is None: |
| 58 | raise ValueError("Payload required for /add endpoint") |
| 59 | |
| 60 | data = json.loads(payload) |
| 61 | user_name = data.get("user") |
| 62 | |
| 63 | # Edge Case: Missing user name in payload |
| 64 | if user_name is None: |
| 65 | raise ValueError("User name is required") |
| 66 | |
| 67 | existing_user = self._find_user(user_name) |
| 68 | if existing_user is not None: |
| 69 | # Return existing user if already exists |
| 70 | return json.dumps(existing_user) |
| 71 | |
| 72 | new_user = { |
| 73 | "name": user_name, |
| 74 | "owes": {}, |
| 75 | "owed_by": {}, |
| 76 | "balance": 0.0 |
| 77 | } |
| 78 | |
| 79 | self.database["users"].append(new_user) |
| 80 | |
| 81 | # Sort users by name after adding |
| 82 | self.database["users"].sort(key=lambda u: u["name"]) |
| 83 | |
| 84 | return json.dumps(new_user) |
| 85 | |
| 86 | elif url == "/iou": |
| 87 | if payload is None: |
| 88 | raise ValueError("Payload required for /iou endpoint") |
| 89 | |
| 90 | data = json.loads(payload) |
| 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 | raise ValueError("Lender, borrower, and amount are all required") |
| 98 | |
| 99 | # Edge Case: Lender and borrower are the same person |
| 100 | if lender_name == borrower_name: |
| 101 | raise ValueError("Lender and borrower cannot be the same person") |
| 102 | |
| 103 | # Edge Case: Negative amount |
| 104 | if amount < 0: |
| 105 | raise ValueError("Amount must be non-negative") |
| 106 | |
| 107 | # Get or create lender |
| 108 | lender = self._find_user(lender_name) |
| 109 | if lender is None: |
| 110 | lender = { |
| 111 | "name": lender_name, |
| 112 | "owes": {}, |
| 113 | "owed_by": {}, |
| 114 | "balance": 0.0 |
| 115 | } |
| 116 | self.database["users"].append(lender) |
| 117 | self.database["users"].sort(key=lambda u: u["name"]) |
| 118 | |
| 119 | # Get or create borrower |
| 120 | borrower = self._find_user(borrower_name) |
| 121 | if borrower is None: |
| 122 | borrower = { |
| 123 | "name": borrower_name, |
| 124 | "owes": {}, |
| 125 | "owed_by": {}, |
| 126 | "balance": 0.0 |
| 127 | } |
| 128 | self.database["users"].append(borrower) |
| 129 | self.database["users"].sort(key=lambda u: u["name"]) |
| 130 | |
| 131 | # Calculate the net change in debt |
| 132 | # When lender lends to borrower, borrower should owe lender more |
| 133 | # But we need to net this with existing debts |
| 134 | |
| 135 | # Get current debts between lender and borrower |
| 136 | borrower_owes_lender = borrower["owes"].get(lender_name, 0) # Amount borrower owes to lender |
| 137 | borrower_owed_by_lender = borrower["owed_by"].get(lender_name, 0) # Amount borrower is owed by lender |
| 138 | |
| 139 | # Net current debt from borrower's perspective: positive means borrower owes lender, negative means lender owes borrower |
| 140 | current_net_debt = borrower_owes_lender - borrower_owed_by_lender |
| 141 | |
| 142 | # Process the IOU by calculating the new net debt |
| 143 | # An IOU represents a transfer of money from lender to borrower |
| 144 | # If there's no existing debt, it creates a new debt |
| 145 | # If there's existing debt, it modifies the existing debt |
| 146 | |
| 147 | if current_net_debt == 0: |
| 148 | # No existing debt, create a new debt |
| 149 | new_net_debt = current_net_debt + amount |
| 150 | else: |
| 151 | # Existing debt, modify it |
| 152 | new_net_debt = current_net_debt - amount |
| 153 | |
| 154 | # Update the records based on the new net debt |
| 155 | if borrower_name in lender["owed_by"]: |
| 156 | del lender["owed_by"][borrower_name] |
| 157 | if borrower_name in lender["owes"]: |
| 158 | del lender["owes"][borrower_name] |
| 159 | |
| 160 | if lender_name in borrower["owed_by"]: |
| 161 | del borrower["owed_by"][lender_name] |
| 162 | if lender_name in borrower["owes"]: |
| 163 | del borrower["owes"][lender_name] |
| 164 | |
| 165 | # Apply the new net debt |
| 166 | if new_net_debt > 0: |
| 167 | # Borrower owes lender |
| 168 | lender["owed_by"][borrower_name] = new_net_debt |
| 169 | borrower["owes"][lender_name] = new_net_debt |
| 170 | elif new_net_debt < 0: |
| 171 | # Lender owes borrower |
| 172 | lender["owes"][borrower_name] = -new_net_debt |
| 173 | borrower["owed_by"][lender_name] = -new_net_debt |
| 174 | # If new_net_debt is 0, no entries are added |
| 175 | |
| 176 | # Recalculate balances |
| 177 | self._recalculate_balance(lender) |
| 178 | self._recalculate_balance(borrower) |
| 179 | |
| 180 | # Recalculate balances |
| 181 | self._recalculate_balance(lender) |
| 182 | self._recalculate_balance(borrower) |
| 183 | |
| 184 | # Recalculate balances |
| 185 | self._recalculate_balance(lender) |
| 186 | self._recalculate_balance(borrower) |
| 187 | |
| 188 | # Return updated users sorted by name |
| 189 | users = [lender, borrower] |
| 190 | users.sort(key=lambda u: u["name"]) |
| 191 | return json.dumps({"users": users}) |
| 192 | |
| 193 | else: |
| 194 | raise ValueError(f"Unknown POST endpoint: {url}") |
| 195 | |
| 196 | def _find_user(self, name: str): |
| 197 | """ |
| 198 | Find a user by name in the database. |
| 199 | |
| 200 | Args: |
| 201 | name: The name of the user to find. |
| 202 | |
| 203 | Returns: |
| 204 | The user dictionary if found, None otherwise. |
| 205 | """ |
| 206 | for user in self.database["users"]: |
| 207 | if user["name"] == name: |
| 208 | return user |
| 209 | return None |
| 210 | |
| 211 | def _recalculate_balance(self, user): |
| 212 | """ |
| 213 | Recalculate the balance for a user based on their owes and owed_by. |
| 214 | |
| 215 | Args: |
| 216 | user: The user dictionary to update. |
| 217 | """ |
| 218 | total_owed_by = sum(user["owed_by"].values()) |
| 219 | total_owes = sum(user["owes"].values()) |
| 220 | user["balance"] = round(total_owed_by - total_owes, 2) |
| 221 | |
| 222 | def _net_debts(self, user, other_user_name): |
| 223 | """ |
| 224 | Net the debts between a user and another user to simplify the ledger. |
| 225 | |
| 226 | Args: |
| 227 | user: The user dictionary to update. |
| 228 | other_user_name: The name of the other user. |
| 229 | """ |
| 230 | amount_owed_by_user = user["owed_by"].get(other_user_name, 0) |
| 231 | amount_owed_to_user = user["owes"].get(other_user_name, 0) |
| 232 | |
| 233 | # Remove the entries if they exist |
| 234 | if other_user_name in user["owed_by"]: |
| 235 | del user["owed_by"][other_user_name] |
| 236 | if other_user_name in user["owes"]: |
| 237 | del user["owes"][other_user_name] |
| 238 | |
| 239 | # Add back the net amount |
| 240 | net_amount = amount_owed_by_user - amount_owed_to_user |
| 241 | if net_amount > 0: |
| 242 | user["owed_by"][other_user_name] = net_amount |
| 243 | elif net_amount < 0: |
| 244 | user["owes"][other_user_name] = -net_amount |
| 245 | # If net_amount is 0, no entry is added (no debt) |
| 246 | |
| 247 | def _get_all_users(self): |
| 248 | """ |
| 249 | Get all users from the database. |
| 250 | |
| 251 | Returns: |
| 252 | A list of all user dictionaries. |
| 253 | """ |
| 254 | return self.database["users"] |
| 255 | |
| 256 | def _get_users_by_names(self, names): |
| 257 | """ |
| 258 | Get specific users by their names. |
| 259 | |
| 260 | Args: |
| 261 | names: A list of user names to retrieve. |
| 262 | |
| 263 | Returns: |
| 264 | A list of user dictionaries sorted by name. |
| 265 | """ |
| 266 | users = [] |
| 267 | for name in names: |
| 268 | user = self._find_user(name) |
| 269 | # Edge Case: Requested user does not exist |
| 270 | if user is not None: |
| 271 | users.append(user) |
| 272 | users.sort(key=lambda u: u["name"]) |
| 273 | return users |
| 274 | |
| 275 | # Handled Edge Cases: Missing user name in payload, user already exists, missing required fields, |
| 276 | # lender and borrower are the same person, negative amount, lender or borrower does not exist, |
| 277 | # requested user does not exist |