| 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 | 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 | # Edge Case: Invalid URL |
| 56 | raise ValueError(f"Invalid URL: {url}") |
| 57 | |
| 8 | 58 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 59 | """ |
| 60 | Handle POST requests to the API. |
| 61 | |
| 62 | Args: |
| 63 | url: The endpoint URL. |
| 64 | payload: JSON payload. |
| 65 | |
| 66 | Returns: |
| 67 | A JSON string response. |
| 68 | |
| 69 | Raises: |
| 70 | ValueError: If the URL is not recognized or payload is invalid. |
| 71 | """ |
| 72 | if payload is None: |
| 73 | # Edge Case: Missing payload |
| 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 |
| 82 | if not user_name: |
| 83 | raise ValueError("User name is required") |
| 84 | |
| 85 | # Edge Case: User already exists |
| 86 | if self._find_user(user_name): |
| 87 | raise ValueError(f"User {user_name} already exists") |
| 88 | |
| 89 | new_user = { |
| 90 | "name": user_name, |
| 91 | "owes": {}, |
| 92 | "owed_by": {}, |
| 93 | "balance": 0.0 |
| 94 | } |
| 95 | self.database["users"].append(new_user) |
| 96 | return json.dumps(self._create_user_object(new_user)) |
| 97 | |
| 98 | elif url == "/iou": |
| 99 | lender_name = data.get("lender") |
| 100 | borrower_name = data.get("borrower") |
| 101 | amount = data.get("amount") |
| 102 | |
| 103 | # Edge Case: Missing required fields |
| 104 | if not lender_name or not borrower_name or amount is None: |
| 105 | raise ValueError("Lender, borrower, and amount are required") |
| 106 | |
| 107 | # Edge Case: Negative amount |
| 108 | if amount < 0: |
| 109 | raise ValueError("Amount must be non-negative") |
| 110 | |
| 111 | # Edge Case: Lender and borrower are the same |
| 112 | if lender_name == borrower_name: |
| 113 | raise ValueError("Lender and borrower cannot be the same person") |
| 114 | |
| 115 | lender = self._find_user(lender_name) |
| 116 | borrower = self._find_user(borrower_name) |
| 117 | |
| 118 | # Edge Case: Non-existent lender or borrower |
| 119 | if not lender: |
| 120 | raise ValueError(f"User {lender_name} does not exist") |
| 121 | if not borrower: |
| 122 | raise ValueError(f"User {borrower_name} does not exist") |
| 123 | |
| 124 | # Handle existing debt relationships properly |
| 125 | # Check if lender already owes borrower (reverse relationship) |
| 126 | existing_lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 127 | |
| 128 | if existing_lender_owes_borrower > 0: |
| 129 | # Lender already owes borrower - offset the existing debt |
| 130 | if amount > existing_lender_owes_borrower: |
| 131 | # New loan exceeds existing debt - remove old debt, create new reverse debt |
| 132 | del lender["owes"][borrower_name] |
| 133 | del borrower["owed_by"][lender_name] # Remove the old debt from borrower |
| 134 | |
| 135 | # Create new debt in reverse direction |
| 136 | new_amount = amount - existing_lender_owes_borrower |
| 137 | lender["owed_by"][borrower_name] = new_amount |
| 138 | borrower["owes"][lender_name] = new_amount |
| 139 | |
| 140 | # Update balances |
| 141 | lender["balance"] += amount |
| 142 | borrower["balance"] -= amount |
| 143 | elif amount < existing_lender_owes_borrower: |
| 144 | # New loan is less than existing debt - reduce existing debt |
| 145 | lender["owes"][borrower_name] = existing_lender_owes_borrower - amount |
| 146 | borrower["owed_by"][lender_name] = existing_lender_owes_borrower - amount |
| 147 | |
| 148 | # Update balances |
| 149 | lender["balance"] += amount |
| 150 | borrower["balance"] -= amount |
| 151 | else: |
| 152 | # New loan equals existing debt - cancel out debts |
| 153 | del lender["owes"][borrower_name] |
| 154 | del borrower["owed_by"][lender_name] |
| 155 | |
| 156 | # Update balances |
| 157 | lender["balance"] += amount |
| 158 | borrower["balance"] -= amount |
| 159 | else: |
| 160 | # No existing reverse debt - create new IOU normally |
| 161 | # Update lender's owed_by |
| 162 | if borrower_name in lender["owed_by"]: |
| 163 | lender["owed_by"][borrower_name] += amount |
| 164 | else: |
| 165 | lender["owed_by"][borrower_name] = amount |
| 166 | |
| 167 | # Update borrower's owes |
| 168 | if lender_name in borrower["owes"]: |
| 169 | borrower["owes"][lender_name] += amount |
| 170 | else: |
| 171 | borrower["owes"][lender_name] = amount |
| 172 | |
| 173 | # Update balances |
| 174 | lender["balance"] += amount |
| 175 | borrower["balance"] -= amount |
| 176 | |
| 177 | # Return updated users |
| 178 | users = [self._create_user_object(lender), self._create_user_object(borrower)] |
| 179 | users.sort(key=lambda u: u["name"]) |
| 180 | return json.dumps({"users": users}) |
| 181 | else: |
| 182 | # Edge Case: Invalid URL |
| 183 | raise ValueError(f"Invalid URL: {url}") |
| 184 | |
| 185 | def _find_user(self, name: str): |
| 186 | """ |
| 187 | Find a user by name in the database. |
| 188 | |
| 189 | Args: |
| 190 | name: The name of the user to find. |
| 191 | |
| 192 | Returns: |
| 193 | The user dictionary if found, None otherwise. |
| 194 | """ |
| 195 | for user in self.database["users"]: |
| 196 | if user["name"] == name: |
| 197 | return user |
| 198 | return None |
| 199 | |
| 200 | def _create_user_object(self, user): |
| 201 | """ |
| 202 | Create a user object for API response. |
| 203 | |
| 204 | Args: |
| 205 | user: The user dictionary from the database. |
| 206 | |
| 207 | Returns: |
| 208 | A dictionary representing the user object for API response. |
| 209 | """ |
| 210 | # Make copies to avoid modifying the original data |
| 211 | owes = user["owes"].copy() |
| 212 | owed_by = user["owed_by"].copy() |
| 213 | balance = round(user["balance"], 2) |
| 214 | |
| 215 | return { |
| 216 | "name": user["name"], |
| 217 | "owes": owes, |
| 218 | "owed_by": owed_by, |
| 219 | "balance": balance |
| 220 | } |
| 221 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Negative amount, Lender and borrower are the same, Non-existent lender or borrower, Empty user list in payload, Non-existent users in payload |