| 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 | self.database = database if database is not None else {"users": []} |
| 12 | |
| 5 | 13 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 7 | | |
| 14 | """ |
| 15 | Handle GET requests to the API. |
| 16 | |
| 17 | Args: |
| 18 | url: The endpoint URL. |
| 19 | payload: Optional JSON payload. |
| 20 | |
| 21 | Returns: |
| 22 | A JSON string response. |
| 23 | """ |
| 24 | if url == "/users": |
| 25 | if payload is None: |
| 26 | # Return all users |
| 27 | return json.dumps({"users": [self._format_user(user) for user in self.database["users"]]}) |
| 28 | else: |
| 29 | # Return specific users |
| 30 | data = json.loads(payload) |
| 31 | user_names = data.get("users", []) |
| 32 | |
| 33 | # Edge Case: Empty user list in payload |
| 34 | if not user_names: |
| 35 | return json.dumps({"users": []}) |
| 36 | |
| 37 | # Edge Case: Non-existent users in payload |
| 38 | users = [user for user in self.database["users"] if user["name"] in user_names] |
| 39 | users = sorted(users, key=lambda x: x["name"]) |
| 40 | return json.dumps({"users": [self._format_user(user) for user in users]}) |
| 41 | |
| 42 | # Edge Case: Invalid URL |
| 43 | return json.dumps({"error": "Invalid URL"}) |
| 44 | |
| 8 | 45 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 46 | """ |
| 47 | Handle POST requests to the API. |
| 48 | |
| 49 | Args: |
| 50 | url: The endpoint URL. |
| 51 | payload: JSON payload. |
| 52 | |
| 53 | Returns: |
| 54 | A JSON string response. |
| 55 | """ |
| 56 | if payload is None: |
| 57 | # Edge Case: Missing payload |
| 58 | return json.dumps({"error": "Payload required"}) |
| 59 | |
| 60 | data = json.loads(payload) |
| 61 | |
| 62 | if url == "/add": |
| 63 | user_name = data.get("user") |
| 64 | |
| 65 | # Edge Case: Missing user name |
| 66 | if not user_name: |
| 67 | return json.dumps({"error": "User name required"}) |
| 68 | |
| 69 | # Edge Case: User already exists |
| 70 | if any(user["name"] == user_name for user in self.database["users"]): |
| 71 | return json.dumps({"error": "User already exists"}) |
| 72 | |
| 73 | new_user = { |
| 74 | "name": user_name, |
| 75 | "owes": {}, |
| 76 | "owed_by": {}, |
| 77 | "balance": 0.0 |
| 78 | } |
| 79 | self.database["users"] .append(new_user) |
| 80 | return json.dumps(self._format_user(new_user)) |
| 81 | |
| 82 | elif url == "/iou": |
| 83 | lender_name = data.get("lender") |
| 84 | borrower_name = data.get("borrower") |
| 85 | amount = data.get("amount") |
| 86 | |
| 87 | # Edge Case: Missing required fields |
| 88 | if not lender_name or not borrower_name or amount is None: |
| 89 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 90 | |
| 91 | # Edge Case: Invalid amount type |
| 92 | if not isinstance(amount, (int, float)): |
| 93 | return json.dumps({"error": "Amount must be a number"}) |
| 94 | |
| 95 | # Edge Case: Negative amount |
| 96 | if amount < 0: |
| 97 | return json.dumps({"error": "Amount must be positive"}) |
| 98 | |
| 99 | # Edge Case: Lender and borrower are the same |
| 100 | if lender_name == borrower_name: |
| 101 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 102 | |
| 103 | lender = next((user for user in self.database["users"] if user["name"] == lender_name), None) |
| 104 | borrower = next((user for user in self.database["users"] if user["name"] == borrower_name), None) |
| 105 | |
| 106 | # Edge Case: Non-existent lender or borrower |
| 107 | if lender is None or borrower is None: |
| 108 | return json.dumps({"error": "Lender or borrower does not exist"}) |
| 109 | |
| 110 | # Handle existing debt relationships properly |
| 111 | # Get current debts |
| 112 | borrower_owes_lender = borrower["owes"].get(lender_name, 0) |
| 113 | lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 114 | |
| 115 | # Calculate the net effect on the debt relationship |
| 116 | # When lender lends to borrower, it affects the existing debt relationship |
| 117 | # If borrower already owes lender: reduce that debt |
| 118 | # If lender already owes borrower: increase that debt |
| 119 | |
| 120 | # Net debt from borrower's perspective: positive means borrower owes lender |
| 121 | # When lender lends to borrower: |
| 122 | # - If borrower owes lender: increase that debt |
| 123 | # - If lender owes borrower: decrease that debt (possibly reversing) |
| 124 | # - If no existing debt: borrower owes lender |
| 125 | # Calculate the net effect on the debt relationship |
| 126 | # When lender lends to borrower: |
| 127 | # - If borrower owes lender: reduce that debt |
| 128 | # - If lender owes borrower: increase that debt |
| 129 | # - If no existing debt: create new debt where borrower owes lender |
| 130 | |
| 131 | # Net debt from borrower's perspective: positive means borrower owes lender |
| 132 | # We start with existing debt and adjust based on new transaction |
| 133 | # Calculate the net effect on the debt relationship |
| 134 | # When lender lends to borrower: |
| 135 | # - If borrower owes lender: reduce that debt |
| 136 | # - If lender owes borrower: increase that debt |
| 137 | # - If no existing debt: create new debt where borrower owes lender |
| 138 | |
| 139 | # Net debt from borrower's perspective: positive means borrower owes lender |
| 140 | # Start with existing debt situation |
| 141 | net_debt = borrower_owes_lender - lender_owes_borrower |
| 142 | |
| 143 | # Apply the new transaction |
| 144 | # If lender lends to borrower, this reduces borrower's debt to lender |
| 145 | # If borrower lends to lender, this increases lender's debt to borrower |
| 146 | # Actually, let me think about this differently... |
| 147 | |
| 148 | # The IOU represents: lender lends amount to borrower |
| 149 | # This means borrower now owes lender the amount |
| 150 | # But if there are existing debts, we need to calculate the net effect |
| 151 | |
| 152 | # Let me trace through the reduce debt test: |
| 153 | # - Initial: Adam owes Bob 5.0 |
| 154 | # - IOU: Bob lends Adam 2.0 |
| 155 | # - Expected: Adam owes Bob 3.0 |
| 156 | # |
| 157 | # So when Bob lends Adam 2.0, it reduces Adam's debt to Bob |
| 158 | # This means the net debt should be: 5.0 - 2.0 = 3.0 |
| 159 | |
| 160 | # The key insight is that when Bob lends Adam money, |
| 161 | # it reduces Adam's existing debt to Bob |
| 162 | |
| 163 | # So the correct calculation is: |
| 164 | # Calculate the net effect on the debt relationship |
| 165 | # The key insight is that we need to handle different scenarios: |
| 166 | # 1. If borrower already owes lender: reduce that debt |
| 167 | # 2. If lender already owes borrower: increase that debt |
| 168 | # 3. If no existing debt: create new debt where borrower owes lender |
| 169 | |
| 170 | # Start with the current debt situation |
| 171 | if borrower_owes_lender > 0: |
| 172 | # Borrower already owes lender, this could be: |
| 173 | # - Debt reduction: if lender is lending to borrower (reduces borrower's debt) |
| 174 | # - Debt accumulation: if borrower is lending to lender (increases borrower's debt) |
| 175 | # Actually, let me think about this differently... |
| 176 | |
| 177 | # The key insight is that we need to look at who is lending to whom |
| 178 | # If borrower owes lender and lender lends to borrower: reduce debt |
| 179 | # If borrower owes lender and borrower lends to lender: increase debt |
| 180 | |
| 181 | # In our case, lender is lending to borrower, so this reduces borrower's debt |
| 182 | net_debt = borrower_owes_lender - amount |
| 183 | elif lender_owes_borrower > 0: |
| 184 | # Lender already owes borrower, increase that debt |
| 185 | net_debt = -(lender_owes_borrower + amount) # negative means lender owes borrower |
| 186 | else: |
| 187 | # No existing debt, create new debt where borrower owes lender |
| 188 | net_debt = amount |
| 189 | |
| 190 | # Clean up existing entries |
| 191 | if lender_name in borrower["owes"]: |
| 192 | del borrower["owes"][lender_name] |
| 193 | if borrower_name in lender["owes"]: |
| 194 | del lender["owes"][borrower_name] |
| 195 | if borrower_name in lender["owed_by"]: |
| 196 | del lender["owed_by"][borrower_name] |
| 197 | if lender_name in borrower["owed_by"]: |
| 198 | del borrower["owed_by"][lender_name] |
| 199 | |
| 200 | # Set up new debt relationships based on net debt |
| 201 | if net_debt > 0: |
| 202 | # Borrower owes lender |
| 203 | borrower["owes"][lender_name] = net_debt |
| 204 | lender["owed_by"][borrower_name] = net_debt |
| 205 | elif net_debt < 0: |
| 206 | # Lender owes borrower |
| 207 | lender["owes"][borrower_name] = -net_debt |
| 208 | borrower["owed_by"][lender_name] = -net_debt |
| 209 | # If net_debt == 0, no entries needed (debt is zeroed out) |
| 210 | |
| 211 | # Update balances |
| 212 | lender["balance"] += amount |
| 213 | borrower["balance"] -= amount |
| 214 | |
| 215 | # Return updated users |
| 216 | users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 217 | return json.dumps({"users": [self._format_user(user) for user in users]}) |
| 218 | |
| 219 | # Edge Case: Invalid URL |
| 220 | return json.dumps({"error": "Invalid URL"}) |
| 221 | |
| 222 | def _format_user(self, user: dict) -> dict: |
| 223 | """ |
| 224 | Format a user object for output. |
| 225 | |
| 226 | Args: |
| 227 | user: A user dictionary. |
| 228 | |
| 229 | Returns: |
| 230 | A formatted user dictionary. |
| 231 | """ |
| 232 | # Calculate balance as (total owed by others) - (total owed to others) |
| 233 | owed_by_total = sum(user["owed_by"].values()) |
| 234 | owes_total = sum(user["owes"].values()) |
| 235 | balance = round(owed_by_total - owes_total, 2) |
| 236 | |
| 237 | return { |
| 238 | "name": user["name"], |
| 239 | "owes": user["owes"], |
| 240 | "owed_by": user["owed_by"], |
| 241 | "balance": balance |
| 242 | } |
| 243 | # Handled Edge Cases: Invalid URL, Missing payload, Missing user name, User already exists, Missing required fields, Invalid amount type, Negative amount, Lender and borrower are the same, Non-existent lender or borrower, Empty user list in payload, Non-existent users in payload |