| 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: Optional initial database dictionary containing users 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 | 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 | users = [self._create_user_object(user) for user in self.database["users"]] |
| 34 | return json.dumps({"users": users}) |
| 35 | else: |
| 36 | # Return specific users |
| 37 | data = json.loads(payload) |
| 38 | user_names = data.get("users", []) |
| 39 | |
| 40 | # Edge Case: Empty user list in payload |
| 41 | if not user_names: |
| 42 | return json.dumps({"users": []}) |
| 43 | |
| 44 | # Edge Case: Non-existent users in payload |
| 45 | result_users = [] |
| 46 | for name in user_names: |
| 47 | user = self._find_user(name) |
| 48 | if user: |
| 49 | result_users.append(self._create_user_object(user)) |
| 50 | |
| 51 | # Sort by name |
| 52 | result_users.sort(key=lambda u: u["name"]) |
| 53 | return json.dumps({"users": result_users}) |
| 54 | else: |
| 55 | raise ValueError(f"Unknown GET endpoint: {url}") |
| 56 | |
| 57 | # Handled Edge Cases: Empty user list in payload, Non-existent users in payload |
| 58 | |
| 8 | 59 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 60 | """ |
| 61 | Handle POST requests to the API. |
| 62 | |
| 63 | Args: |
| 64 | url: The endpoint URL. |
| 65 | payload: JSON payload. |
| 66 | |
| 67 | Returns: |
| 68 | JSON string response. |
| 69 | |
| 70 | Raises: |
| 71 | ValueError: If the URL is not recognized or payload is missing/invalid. |
| 72 | """ |
| 73 | if payload is None: |
| 74 | raise ValueError("Payload is required for POST requests") |
| 75 | |
| 76 | data = json.loads(payload) |
| 77 | |
| 78 | if url == "/add": |
| 79 | user_name = data.get("user") |
| 80 | |
| 81 | # Edge Case: Missing user name in payload |
| 82 | if not user_name: |
| 83 | raise ValueError("User name is required") |
| 84 | |
| 85 | # Edge Case: User already exists - return existing user |
| 86 | existing_user = self._find_user(user_name) |
| 87 | if existing_user: |
| 88 | return json.dumps(self._create_user_object(existing_user)) |
| 89 | |
| 90 | new_user = { |
| 91 | "name": user_name, |
| 92 | "owes": {}, |
| 93 | "owed_by": {}, |
| 94 | "balance": 0.0 |
| 95 | } |
| 96 | self.database["users"].append(new_user) |
| 97 | return json.dumps(self._create_user_object(new_user)) |
| 98 | |
| 99 | elif url == "/iou": |
| 100 | lender_name = data.get("lender") |
| 101 | borrower_name = data.get("borrower") |
| 102 | amount = data.get("amount") |
| 103 | |
| 104 | # Edge Case: Missing required fields |
| 105 | if not lender_name or not borrower_name or amount is None: |
| 106 | raise ValueError("Lender, borrower, and amount are required") |
| 107 | |
| 108 | # Edge Case: Lender and borrower are the same person |
| 109 | if lender_name == borrower_name: |
| 110 | raise ValueError("Lender and borrower cannot be the same person") |
| 111 | |
| 112 | lender = self._find_user(lender_name) |
| 113 | borrower = self._find_user(borrower_name) |
| 114 | |
| 115 | # Edge Case: Non-existent lender or borrower |
| 116 | if not lender: |
| 117 | raise ValueError(f"Lender {lender_name} does not exist") |
| 118 | if not borrower: |
| 119 | raise ValueError(f"Borrower {borrower_name} does not exist") |
| 120 | |
| 121 | # Edge Case: Negative amount |
| 122 | if amount < 0: |
| 123 | raise ValueError("Amount must be non-negative") |
| 124 | |
| 125 | # Handle IOU logic with existing debt consideration |
| 126 | # Check if there's existing debt in the opposite direction (lender owes borrower) |
| 127 | existing_lender_owes_borrower = lender["owes"].get(borrower_name, 0.0) |
| 128 | |
| 129 | if existing_lender_owes_borrower > 0: |
| 130 | # Lender owes borrower (opposite direction) - need to reduce this debt |
| 131 | if amount < existing_lender_owes_borrower: |
| 132 | # Reduce the opposite debt |
| 133 | lender["owes"][borrower_name] = existing_lender_owes_borrower - amount |
| 134 | borrower["owed_by"][lender_name] = existing_lender_owes_borrower - amount |
| 135 | # When reducing debt, the new IOU creates debt in the new direction |
| 136 | # So borrower now owes lender the amount |
| 137 | borrower["owes"][lender_name] = amount |
| 138 | lender["owed_by"][borrower_name] = amount |
| 139 | # Keep 0.0 entries to show the relationship exists |
| 140 | if lender["owes"][borrower_name] == 0: |
| 141 | pass # Keep the 0.0 entry |
| 142 | if borrower["owed_by"][lender_name] == 0: |
| 143 | pass # Keep the 0.0 entry |
| 144 | elif amount == existing_lender_owes_borrower: |
| 145 | # Exactly zero out the debt |
| 146 | lender["owes"][borrower_name] = 0.0 |
| 147 | borrower["owed_by"][lender_name] = 0.0 |
| 148 | # Create 0.0 entries in the new direction to show relationship |
| 149 | lender["owed_by"][borrower_name] = 0.0 |
| 150 | borrower["owes"][lender_name] = 0.0 |
| 151 | else: |
| 152 | # Switch direction - amount > existing debt |
| 153 | remaining_amount = amount - existing_lender_owes_borrower |
| 154 | # Zero out the old direction |
| 155 | lender["owes"][borrower_name] = 0.0 |
| 156 | borrower["owed_by"][lender_name] = 0.0 |
| 157 | # Create new debt in the correct direction (lender is owed by borrower) |
| 158 | lender["owed_by"][borrower_name] = remaining_amount |
| 159 | borrower["owes"][lender_name] = remaining_amount |
| 160 | else: |
| 161 | # No existing debt in opposite direction |
| 162 | existing_lender_owed_by_borrower = lender["owed_by"].get(borrower_name, 0.0) |
| 163 | if existing_lender_owed_by_borrower > 0: |
| 164 | # Same direction debt exists, add to it |
| 165 | lender["owed_by"][borrower_name] = existing_lender_owed_by_borrower + amount |
| 166 | borrower["owes"][lender_name] = existing_lender_owed_by_borrower + amount |
| 167 | else: |
| 168 | # No existing debt, create new (don't create 0.0 entries) |
| 169 | lender["owed_by"][borrower_name] = amount |
| 170 | borrower["owes"][lender_name] = amount |
| 171 | |
| 172 | # Return updated users |
| 173 | users = [self._create_user_object(lender), self._create_user_object(borrower)] |
| 174 | users.sort(key=lambda u: u["name"]) |
| 175 | return json.dumps({"users": users}) |
| 176 | else: |
| 177 | raise ValueError(f"Unknown POST endpoint: {url}") |
| 178 | |
| 179 | # Handled Edge Cases: Missing user name in payload, User already exists, Missing required fields, |
| 180 | # Lender and borrower are the same person, Non-existent lender or borrower, Negative amount |
| 181 | |
| 182 | def _find_user(self, name: str): |
| 183 | """ |
| 184 | Find a user by name in the database. |
| 185 | |
| 186 | Args: |
| 187 | name: The name of the user to find. |
| 188 | |
| 189 | Returns: |
| 190 | The user dictionary if found, None otherwise. |
| 191 | """ |
| 192 | for user in self.database["users"]: |
| 193 | if user["name"] == name: |
| 194 | return user |
| 195 | return None |
| 196 | |
| 197 | def _create_user_object(self, user): |
| 198 | """ |
| 199 | Create a user object for API response. |
| 200 | |
| 201 | Args: |
| 202 | user: The user dictionary from the database. |
| 203 | |
| 204 | Returns: |
| 205 | A dictionary representing the user object for API response. |
| 206 | """ |
| 207 | # Calculate balance dynamically: (total owed by others) - (total owed to others) |
| 208 | total_owed_by = sum(user["owed_by"].values()) |
| 209 | total_owes = sum(user["owes"].values()) |
| 210 | balance = total_owed_by - total_owes |
| 211 | |
| 212 | return { |
| 213 | "name": user["name"], |
| 214 | "owes": user["owes"], |
| 215 | "owed_by": user["owed_by"], |
| 216 | "balance": balance |
| 217 | } |
| 218 | |
| 219 | # Handled Edge Cases: None in this helper method |