| 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 | # Edge Case: Handle None database by initializing empty structure |
| 12 | if database is None: |
| 13 | self.database = {"users": []} |
| 14 | else: |
| 15 | self.database = database |
| 16 | |
| 5 | 17 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 18 | """ |
| 19 | Handle GET requests to the API. |
| 20 | |
| 21 | Args: |
| 22 | url: The endpoint URL. |
| 23 | payload: Optional JSON payload. |
| 24 | |
| 25 | Returns: |
| 26 | JSON string response. |
| 27 | """ |
| 28 | if url == "/users": |
| 29 | # Edge Case: Handle missing payload |
| 30 | if payload is None: |
| 31 | users = self._get_all_users() |
| 32 | return json.dumps({"users": users}) |
| 33 | else: |
| 34 | data = json.loads(payload) |
| 35 | # Edge Case: Handle missing 'users' key in payload |
| 36 | if "users" not in data: |
| 37 | return json.dumps({"users": []}) |
| 38 | user_names = data["users"] |
| 39 | users = self._get_users_by_names(user_names) |
| 40 | return json.dumps({"users": users}) |
| 41 | # Edge Case: Handle unknown URL |
| 42 | return json.dumps({"error": "Not found"}) |
| 43 | |
| 8 | 44 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 45 | """ |
| 46 | Handle POST requests to the API. |
| 47 | |
| 48 | Args: |
| 49 | url: The endpoint URL. |
| 50 | payload: JSON payload. |
| 51 | |
| 52 | Returns: |
| 53 | JSON string response. |
| 54 | """ |
| 55 | # Edge Case: Handle missing payload |
| 56 | if payload is None: |
| 57 | return json.dumps({"error": "Payload required"}) |
| 58 | |
| 59 | data = json.loads(payload) |
| 60 | |
| 61 | if url == "/add": |
| 62 | # Edge Case: Handle missing 'user' key in payload |
| 63 | if "user" not in data: |
| 64 | return json.dumps({"error": "Missing user field"}) |
| 65 | user_name = data["user"] |
| 66 | # Edge Case: Handle duplicate user |
| 67 | if self._user_exists(user_name): |
| 68 | return json.dumps({"error": "User already exists"}) |
| 69 | user = self._create_user(user_name) |
| 70 | return json.dumps(user) |
| 71 | elif url == "/iou": |
| 72 | # Edge Case: Handle missing required fields |
| 73 | required_fields = ["lender", "borrower", "amount"] |
| 74 | for field in required_fields: |
| 75 | if field not in data: |
| 76 | return json.dumps({"error": f"Missing {field} field"}) |
| 77 | |
| 78 | lender_name = data["lender"] |
| 79 | borrower_name = data["borrower"] |
| 80 | amount = data["amount"] |
| 81 | |
| 82 | # Edge Case: Handle invalid amount type |
| 83 | if not isinstance(amount, (int, float)): |
| 84 | return json.dumps({"error": "Invalid amount"}) |
| 85 | |
| 86 | # Edge Case: Handle negative amount |
| 87 | if amount < 0: |
| 88 | return json.dumps({"error": "Amount must be positive"}) |
| 89 | |
| 90 | # Edge Case: Handle lender and borrower being the same person |
| 91 | if lender_name == borrower_name: |
| 92 | return json.dumps({"error": "Cannot create IOU between same user"}) |
| 93 | |
| 94 | # Create users if they don't exist |
| 95 | if not self._user_exists(lender_name): |
| 96 | self._create_user(lender_name) |
| 97 | if not self._user_exists(borrower_name): |
| 98 | self._create_user(borrower_name) |
| 99 | |
| 100 | self._update_iou(lender_name, borrower_name, amount) |
| 101 | users = self._get_users_by_names([lender_name, borrower_name]) |
| 102 | return json.dumps({"users": users}) |
| 103 | # Edge Case: Handle unknown URL |
| 104 | return json.dumps({"error": "Not found"}) |
| 105 | |
| 106 | def _get_all_users(self) -> list: |
| 107 | """ |
| 108 | Get all users from the database. |
| 109 | |
| 110 | Returns: |
| 111 | List of user objects. |
| 112 | """ |
| 113 | users = [] |
| 114 | for user_data in self.database["users"]: |
| 115 | user = self._build_user_object(user_data) |
| 116 | users.append(user) |
| 117 | users.sort(key=lambda x: x["name"]) |
| 118 | return users |
| 119 | |
| 120 | def _get_users_by_names(self, names: list) -> list: |
| 121 | """ |
| 122 | Get user objects for specified names, sorted by name. |
| 123 | |
| 124 | Args: |
| 125 | names: List of user names. |
| 126 | |
| 127 | Returns: |
| 128 | List of user objects sorted by name. |
| 129 | """ |
| 130 | users = [] |
| 131 | for user_data in self.database["users"]: |
| 132 | if user_data["name"] in names: |
| 133 | user = self._build_user_object(user_data) |
| 134 | users.append(user) |
| 135 | users.sort(key=lambda x: x["name"]) |
| 136 | return users |
| 137 | |
| 138 | def _user_exists(self, name: str) -> bool: |
| 139 | """ |
| 140 | Check if a user exists in the database. |
| 141 | |
| 142 | Args: |
| 143 | name: User name to check. |
| 144 | |
| 145 | Returns: |
| 146 | True if user exists, False otherwise. |
| 147 | """ |
| 148 | for user in self.database["users"]: |
| 149 | if user["name"] == name: |
| 150 | return True |
| 151 | return False |
| 152 | |
| 153 | def _create_user(self, name: str) -> dict: |
| 154 | """ |
| 155 | Create a new user in the database. |
| 156 | |
| 157 | Args: |
| 158 | name: Name of the new user. |
| 159 | |
| 160 | Returns: |
| 161 | User object for the new user. |
| 162 | """ |
| 163 | user = { |
| 164 | "name": name, |
| 165 | "owes": {}, |
| 166 | "owed_by": {}, |
| 167 | "balance": 0.0 |
| 168 | } |
| 169 | self.database["users"] .append({ |
| 170 | "name": name, |
| 171 | "owes": {}, |
| 172 | "owed_by": {} |
| 173 | }) |
| 174 | return user |
| 175 | |
| 176 | def _build_user_object(self, user_data: dict) -> dict: |
| 177 | """ |
| 178 | Build a complete user object with calculated balance. |
| 179 | |
| 180 | Args: |
| 181 | user_data: Raw user data from database. |
| 182 | |
| 183 | Returns: |
| 184 | Complete user object with balance. |
| 185 | """ |
| 186 | owes = user_data.get("owes", {}) |
| 187 | owed_by = user_data.get("owed_by", {}) |
| 188 | |
| 189 | total_owes = sum(owes.values()) |
| 190 | total_owed_by = sum(owed_by.values()) |
| 191 | balance = round(total_owed_by - total_owes, 2) |
| 192 | |
| 193 | return { |
| 194 | "name": user_data["name"], |
| 195 | "owes": owes, |
| 196 | "owed_by": owed_by, |
| 197 | "balance": balance |
| 198 | } |
| 199 | |
| 200 | def _update_iou(self, lender_name: str, borrower_name: str, amount: float) -> None: |
| 201 | """ |
| 202 | Update IOU records between lender and borrower. |
| 203 | |
| 204 | Args: |
| 205 | lender_name: Name of the lender. |
| 206 | borrower_name: Name of the borrower. |
| 207 | amount: Amount of the IOU. |
| 208 | """ |
| 209 | amount = round(amount, 2) |
| 210 | |
| 211 | # Find lender and borrower in database |
| 212 | lender = None |
| 213 | borrower = None |
| 214 | |
| 215 | for user in self.database["users"]: |
| 216 | if user["name"] == lender_name: |
| 217 | lender = user |
| 218 | elif user["name"] == borrower_name: |
| 219 | borrower = user |
| 220 | |
| 221 | # When A lends amount X to B: |
| 222 | # 1. Reduce what B owes to A (if any) |
| 223 | # 2. Increase what A is owed by B with remaining amount |
| 224 | |
| 225 | # Get current amounts |
| 226 | borrower_owes_lender = borrower["owes"].get(lender_name, 0) |
| 227 | lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 228 | lender_owed_by_borrower = lender["owed_by"].get(borrower_name, 0) |
| 229 | borrower_owed_by_lender = borrower["owed_by"].get(lender_name, 0) |
| 230 | |
| 231 | # Clean up any existing entries for this transaction |
| 232 | # Remove entries that will be recalculated |
| 233 | if lender_name in borrower["owes"]: |
| 234 | del borrower["owes"][lender_name] |
| 235 | if borrower_name in lender["owed_by"]: |
| 236 | del lender["owed_by"][borrower_name] |
| 237 | if borrower_name in lender["owes"]: |
| 238 | del lender["owes"][borrower_name] |
| 239 | if lender_name in borrower["owed_by"]: |
| 240 | del borrower["owed_by"][lender_name] |
| 241 | |
| 242 | # Calculate net effect |
| 243 | # Net debt from borrower to lender = (what borrower owes lender) + (new amount) - (what lender owes borrower) |
| 244 | net_debt = borrower_owes_lender + amount - lender_owes_borrower |
| 245 | |
| 246 | if net_debt > 0: |
| 247 | # Borrower owes lender |
| 248 | borrower["owes"][lender_name] = net_debt |
| 249 | lender["owed_by"][borrower_name] = net_debt |
| 250 | elif net_debt < 0: |
| 251 | # Lender owes borrower |
| 252 | lender["owes"][borrower_name] = abs(net_debt) |
| 253 | borrower["owed_by"][lender_name] = abs(net_debt) |
| 254 | # If net_debt == 0, no entries needed (debts cancel out) |
| 255 | # Handled Edge Cases: None database, missing payload, missing 'users' key, unknown URL, missing 'user' key, duplicate user, missing required fields, invalid amount type, negative amount, non-existent users, same lender/borrower |