| 1 | import json |
| 2 | from typing import Dict, List, Optional, Any |
| 3 | |
| 1 | 4 | class RestAPI: |
| 2 | 5 | def __init__(self, database: dict | None = None): |
| 3 | | pass |
| 4 | | |
| 6 | """ |
| 7 | Initialize the REST API with an optional database. |
| 8 | |
| 9 | Args: |
| 10 | database: A dictionary containing initial user data. |
| 11 | """ |
| 12 | self.database = database or {"users": []} |
| 13 | # Ensure all users have the required fields |
| 14 | for user in self.database["users"]: |
| 15 | if "owes" not in user: |
| 16 | user["owes"] = {} |
| 17 | if "owed_by" not in user: |
| 18 | user["owed_by"] = {} |
| 19 | if "balance" not in user: |
| 20 | user["balance"] = 0.0 |
| 21 | |
| 22 | def get_user(self, name: str) -> Optional[Dict]: |
| 23 | """ |
| 24 | Retrieve a user by name from the database. |
| 25 | |
| 26 | Args: |
| 27 | name: The name of the user to retrieve. |
| 28 | |
| 29 | Returns: |
| 30 | The user dictionary if found, None otherwise. |
| 31 | """ |
| 32 | for user in self.database["users"]: |
| 33 | if user["name"] == name: |
| 34 | return user |
| 35 | return None |
| 36 | |
| 37 | def calculate_balance(self, user: Dict) -> float: |
| 38 | """ |
| 39 | Calculate the balance for a user based on what they owe and are owed. |
| 40 | |
| 41 | Args: |
| 42 | user: The user dictionary. |
| 43 | |
| 44 | Returns: |
| 45 | The calculated balance. |
| 46 | """ |
| 47 | total_owed_by = sum(user.get("owed_by", {}).values()) |
| 48 | total_owes = sum(user.get("owes", {}).values()) |
| 49 | return round(total_owed_by - total_owes, 2) |
| 50 | |
| 5 | 51 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 52 | """ |
| 53 | Handle GET requests to the API. |
| 54 | |
| 55 | Args: |
| 56 | url: The endpoint URL. |
| 57 | payload: Optional JSON payload. |
| 58 | |
| 59 | Returns: |
| 60 | JSON response as a string. |
| 61 | """ |
| 62 | if url == "/users": |
| 63 | # Edge Case: Handle request with no payload (list all users) |
| 64 | if payload is None: |
| 65 | # Return all users with updated balances |
| 66 | for user in self.database["users"]: |
| 67 | user["balance"] = self.calculate_balance(user) |
| 68 | # Sort users by name |
| 69 | self.database["users"].sort(key=lambda x: x["name"]) |
| 70 | return json.dumps(self.database) |
| 71 | |
| 72 | # Edge Case: Handle request with payload (list specific users) |
| 73 | try: |
| 74 | data = json.loads(payload) |
| 75 | if "users" not in data: |
| 76 | return json.dumps({"error": "Invalid payload"}) |
| 77 | |
| 78 | # Filter users by the provided list |
| 79 | result_users = [] |
| 80 | for username in sorted(data["users"]): # Sort by name as required |
| 81 | user = self.get_user(username) |
| 82 | if user: |
| 83 | user["balance"] = self.calculate_balance(user) |
| 84 | result_users.append(user) |
| 85 | |
| 86 | return json.dumps({"users": result_users}) |
| 87 | except json.JSONDecodeError: |
| 88 | return json.dumps({"error": "Invalid JSON payload"}) |
| 89 | |
| 90 | return json.dumps({"error": "Invalid URL"}) |
| 91 | # Handled Edge Cases: Request with no payload, request with valid payload, request with invalid payload, invalid JSON payload |
| 92 | |
| 8 | 93 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 94 | """ |
| 95 | Handle POST requests to the API. |
| 96 | |
| 97 | Args: |
| 98 | url: The endpoint URL. |
| 99 | payload: JSON payload. |
| 100 | |
| 101 | Returns: |
| 102 | JSON response as a string. |
| 103 | """ |
| 104 | if payload is None: |
| 105 | return json.dumps({"error": "Payload required"}) |
| 106 | |
| 107 | try: |
| 108 | data = json.loads(payload) |
| 109 | except json.JSONDecodeError: |
| 110 | return json.dumps({"error": "Invalid JSON payload"}) |
| 111 | |
| 112 | if url == "/add": |
| 113 | # Edge Case: Handle adding a new user |
| 114 | if "user" not in data: |
| 115 | return json.dumps({"error": "Missing user field"}) |
| 116 | |
| 117 | username = data["user"] |
| 118 | |
| 119 | # Edge Case: Handle attempt to add a user that already exists |
| 120 | if self.get_user(username) is not None: |
| 121 | return json.dumps({"error": "User already exists"}) |
| 122 | |
| 123 | # Create new user |
| 124 | new_user = { |
| 125 | "name": username, |
| 126 | "owes": {}, |
| 127 | "owed_by": {}, |
| 128 | "balance": 0.0 |
| 129 | } |
| 130 | |
| 131 | self.database["users"].append(new_user) |
| 132 | return json.dumps(new_user) |
| 133 | # Handled Edge Cases: Missing user field, user already exists |
| 134 | |
| 135 | elif url == "/iou": |
| 136 | # Edge Case: Handle creating an IOU |
| 137 | required_fields = ["lender", "borrower", "amount"] |
| 138 | for field in required_fields: |
| 139 | if field not in data: |
| 140 | return json.dumps({"error": f"Missing {field} field"}) |
| 141 | |
| 142 | lender_name = data["lender"] |
| 143 | borrower_name = data["borrower"] |
| 144 | amount = data["amount"] |
| 145 | |
| 146 | # Edge Case: Handle invalid amount (non-numeric or negative) |
| 147 | if not isinstance(amount, (int, float)) or amount < 0: |
| 148 | return json.dumps({"error": "Invalid amount"}) |
| 149 | |
| 150 | lender = self.get_user(lender_name) |
| 151 | borrower = self.get_user(borrower_name) |
| 152 | |
| 153 | # Edge Case: Handle lender or borrower not existing |
| 154 | if lender is None or borrower is None: |
| 155 | return json.dumps({"error": "User does not exist"}) |
| 156 | |
| 157 | # Edge Case: Handle lender and borrower being the same person |
| 158 | if lender_name == borrower_name: |
| 159 | # Return the user unchanged |
| 160 | lender["balance"] = self.calculate_balance(lender) |
| 161 | return json.dumps({"users": [lender]}) |
| 162 | |
| 163 | # Update debts with netting logic |
| 164 | # Get current net debt from lender's perspective |
| 165 | # Positive means lender is owed by borrower |
| 166 | # Negative means lender owes borrower |
| 167 | current_net_debt = lender["owed_by"].get(borrower_name, 0) - lender["owes"].get(borrower_name, 0) |
| 168 | |
| 169 | # When lender lends borrower amount, it creates a debt where borrower owes lender |
| 170 | # But we need to net this with existing debts |
| 171 | # The transaction amount is added to what the borrower owes the lender |
| 172 | new_net_debt = current_net_debt + amount |
| 173 | |
| 174 | # Update the debts based on the new net position |
| 175 | if new_net_debt > 0: |
| 176 | # Lender is owed by borrower |
| 177 | lender["owed_by"][borrower_name] = new_net_debt |
| 178 | borrower["owes"][lender_name] = new_net_debt |
| 179 | # Remove any reverse debt entries |
| 180 | lender["owes"].pop(borrower_name, None) |
| 181 | borrower["owed_by"].pop(lender_name, None) |
| 182 | elif new_net_debt < 0: |
| 183 | # Borrower is owed by lender (lender owes borrower) |
| 184 | absolute_debt = abs(new_net_debt) |
| 185 | lender["owes"][borrower_name] = absolute_debt |
| 186 | borrower["owed_by"][lender_name] = absolute_debt |
| 187 | # Remove any reverse debt entries |
| 188 | lender["owed_by"].pop(borrower_name, None) |
| 189 | borrower["owes"].pop(lender_name, None) |
| 190 | else: |
| 191 | # No debt |
| 192 | lender["owed_by"].pop(borrower_name, None) |
| 193 | lender["owes"].pop(borrower_name, None) |
| 194 | borrower["owed_by"].pop(lender_name, None) |
| 195 | borrower["owes"].pop(lender_name, None) |
| 196 | |
| 197 | # Recalculate balances |
| 198 | lender["balance"] = self.calculate_balance(lender) |
| 199 | borrower["balance"] = self.calculate_balance(borrower) |
| 200 | |
| 201 | # Return updated users sorted by name |
| 202 | result_users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 203 | return json.dumps({"users": result_users}) |
| 204 | # Handled Edge Cases: Missing fields, invalid amount, lender equals borrower, user does not exist |
| 205 | |
| 206 | return json.dumps({"error": "Invalid URL"}) |
| 207 | # Handled Edge Cases: Missing payload, invalid JSON payload, invalid URL |