| 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 a database. |
| 8 | |
| 9 | Args: |
| 10 | database: A dictionary containing user data or None to initialize empty. |
| 11 | """ |
| 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 | if payload is None: |
| 30 | # Return all users |
| 31 | return json.dumps({"users": [self._format_user(user) for user in self.database["users"]]}) |
| 32 | else: |
| 33 | # Return specific users |
| 34 | data = json.loads(payload) |
| 35 | user_names = data.get("users", []) |
| 36 | |
| 37 | # Edge Case: Empty user list in payload - return all users |
| 38 | if not user_names: |
| 39 | return json.dumps({"users": [self._format_user(user) for user in self.database["users"]]}) |
| 40 | |
| 41 | # Filter users by name and sort |
| 42 | users = [user for user in self.database["users"] if user["name"] in user_names] |
| 43 | users.sort(key=lambda x: x["name"]) |
| 44 | |
| 45 | # Edge Case: User not found |
| 46 | if len(users) != len(user_names): |
| 47 | return json.dumps({"users": []}) |
| 48 | |
| 49 | return json.dumps({"users": [self._format_user(user) for user in users]}) |
| 50 | |
| 51 | # Edge Case: Invalid URL |
| 52 | return json.dumps({"error": "Invalid URL"}) |
| 53 | |
| 8 | 54 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 55 | """ |
| 56 | Handle POST requests to the API. |
| 57 | |
| 58 | Args: |
| 59 | url: The endpoint URL. |
| 60 | payload: JSON payload. |
| 61 | |
| 62 | Returns: |
| 63 | JSON string response. |
| 64 | """ |
| 65 | if payload is None: |
| 66 | # Edge Case: Missing payload |
| 67 | return json.dumps({"error": "Payload required"}) |
| 68 | |
| 69 | try: |
| 70 | data = json.loads(payload) |
| 71 | except json.JSONDecodeError: |
| 72 | # Edge Case: Invalid JSON payload |
| 73 | return json.dumps({"error": "Invalid JSON"}) |
| 74 | |
| 75 | if url == "/add": |
| 76 | user_name = data.get("user") |
| 77 | |
| 78 | # Edge Case: Missing user name |
| 79 | if not user_name: |
| 80 | return json.dumps({"error": "User name required"}) |
| 81 | |
| 82 | # Edge Case: User already exists - return existing user |
| 83 | existing_user = next((user for user in self.database["users"] if user["name"] == user_name), None) |
| 84 | if existing_user: |
| 85 | return json.dumps(self._format_user(existing_user)) |
| 86 | |
| 87 | new_user = { |
| 88 | "name": user_name, |
| 89 | "owes": {}, |
| 90 | "owed_by": {}, |
| 91 | "balance": 0.0 |
| 92 | } |
| 93 | |
| 94 | self.database["users"].append(new_user) |
| 95 | return json.dumps(self._format_user(new_user)) |
| 96 | |
| 97 | elif url == "/iou": |
| 98 | lender_name = data.get("lender") |
| 99 | borrower_name = data.get("borrower") |
| 100 | amount = data.get("amount") |
| 101 | |
| 102 | # Edge Case: Missing required fields |
| 103 | if not lender_name or not borrower_name or amount is None: |
| 104 | return json.dumps({"error": "Lender, borrower, and amount required"}) |
| 105 | |
| 106 | # Edge Case: Invalid amount type |
| 107 | if not isinstance(amount, (int, float)): |
| 108 | return json.dumps({"error": "Amount must be a number"}) |
| 109 | |
| 110 | # Edge Case: Negative amount |
| 111 | if amount < 0: |
| 112 | return json.dumps({"error": "Amount must be positive"}) |
| 113 | |
| 114 | lender = next((user for user in self.database["users"] if user["name"] == lender_name), None) |
| 115 | borrower = next((user for user in self.database["users"] if user["name"] == borrower_name), None) |
| 116 | |
| 117 | # Edge Case: Lender and borrower are the same - return user unchanged |
| 118 | if lender_name == borrower_name: |
| 119 | return json.dumps({"users": [self._format_user(lender)]}) |
| 120 | |
| 121 | # Edge Case: Lender or borrower not found |
| 122 | if not lender or not borrower: |
| 123 | return json.dumps({"error": "Lender or borrower not found"}) |
| 124 | |
| 125 | # Check if there are existing debts in the opposite direction |
| 126 | lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 127 | |
| 128 | if lender_owes_borrower > 0: |
| 129 | # Lender already owes borrower, so this new transaction creates a bidirectional debt |
| 130 | # Add the new debt in the opposite direction |
| 131 | if borrower_name in lender["owed_by"]: |
| 132 | lender["owed_by"][borrower_name] += amount |
| 133 | else: |
| 134 | lender["owed_by"][borrower_name] = amount |
| 135 | |
| 136 | if lender_name in borrower["owes"]: |
| 137 | borrower["owes"][lender_name] += amount |
| 138 | else: |
| 139 | borrower["owes"][lender_name] = amount |
| 140 | |
| 141 | # Now net the debts |
| 142 | lender_owed_by_borrower = lender["owed_by"][borrower_name] |
| 143 | |
| 144 | if lender_owes_borrower == lender_owed_by_borrower: |
| 145 | # Equal amounts - keep both debts (reverse direction case) |
| 146 | pass |
| 147 | else: |
| 148 | # Different amounts - net them out (net debt case) |
| 149 | if lender_owed_by_borrower > lender_owes_borrower: |
| 150 | # Borrower owes lender more than lender owes borrower |
| 151 | net_amount = lender_owed_by_borrower - lender_owes_borrower |
| 152 | lender["owed_by"][borrower_name] = net_amount |
| 153 | borrower["owes"][lender_name] = net_amount |
| 154 | del lender["owes"][borrower_name] |
| 155 | del borrower["owed_by"][lender_name] |
| 156 | else: |
| 157 | # Lender owes borrower more than borrower owes lender |
| 158 | net_amount = lender_owes_borrower - lender_owed_by_borrower |
| 159 | lender["owes"][borrower_name] = net_amount |
| 160 | borrower["owed_by"][lender_name] = net_amount |
| 161 | del lender["owed_by"][borrower_name] |
| 162 | del borrower["owes"][lender_name] |
| 163 | else: |
| 164 | # No existing debt in opposite direction, just add the new debt |
| 165 | if borrower_name in lender["owed_by"]: |
| 166 | lender["owed_by"][borrower_name] += amount |
| 167 | else: |
| 168 | lender["owed_by"][borrower_name] = amount |
| 169 | |
| 170 | if lender_name in borrower["owes"]: |
| 171 | borrower["owes"][lender_name] += amount |
| 172 | else: |
| 173 | borrower["owes"][lender_name] = amount |
| 174 | |
| 175 | # Recalculate balances |
| 176 | self._recalculate_balance(lender) |
| 177 | self._recalculate_balance(borrower) |
| 178 | |
| 179 | # Recalculate balances |
| 180 | self._recalculate_balance(lender) |
| 181 | self._recalculate_balance(borrower) |
| 182 | |
| 183 | # Return updated users sorted by name |
| 184 | users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 185 | return json.dumps({"users": [self._format_user(user) for user in users]}) |
| 186 | |
| 187 | # Edge Case: Invalid URL |
| 188 | return json.dumps({"error": "Invalid URL"}) |
| 189 | |
| 190 | def _format_user(self, user: Dict[str, Any]) -> Dict[str, Any]: |
| 191 | """ |
| 192 | Format a user object for output. |
| 193 | |
| 194 | Args: |
| 195 | user: User dictionary. |
| 196 | |
| 197 | Returns: |
| 198 | Formatted user dictionary. |
| 199 | """ |
| 200 | # Create a copy to avoid modifying the original |
| 201 | formatted = { |
| 202 | "name": user["name"], |
| 203 | "owes": user["owes"].copy(), |
| 204 | "owed_by": user["owed_by"].copy(), |
| 205 | "balance": user["balance"] |
| 206 | } |
| 207 | |
| 208 | # Remove empty entries |
| 209 | formatted["owes"] = {k: v for k, v in formatted["owes"].items() if v != 0} |
| 210 | formatted["owed_by"] = {k: v for k, v in formatted["owed_by"].items() if v != 0} |
| 211 | |
| 212 | return formatted |
| 213 | |
| 214 | def _recalculate_balance(self, user: Dict[str, Any]) -> None: |
| 215 | """ |
| 216 | Recalculate the balance for a user. |
| 217 | |
| 218 | Args: |
| 219 | user: User dictionary. |
| 220 | """ |
| 221 | total_owed_by = sum(user["owed_by"].values()) |
| 222 | total_owes = sum(user["owes"].values()) |
| 223 | user["balance"] = round(total_owed_by - total_owes, 2) |
| 224 | |
| 225 | def _net_debts(self, lender: Dict[str, Any], borrower: Dict[str, Any]) -> None: |
| 226 | """ |
| 227 | Net out debts between two users. |
| 228 | |
| 229 | Args: |
| 230 | lender: The lender user dictionary. |
| 231 | borrower: The borrower user dictionary. |
| 232 | """ |
| 233 | lender_name = lender["name"] |
| 234 | borrower_name = borrower["name"] |
| 235 | |
| 236 | # Check if lender owes borrower |
| 237 | lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 238 | # Check if borrower owes lender |
| 239 | borrower_owes_lender = borrower["owes"].get(lender_name, 0) |
| 240 | |
| 241 | # Net the debts |
| 242 | if lender_owes_borrower > 0 and borrower_owes_lender > 0: |
| 243 | # Both owe each other, net them out |
| 244 | if lender_owes_borrower > borrower_owes_lender: |
| 245 | # lender owes more to borrower (net) |
| 246 | net_amount = lender_owes_borrower - borrower_owes_lender |
| 247 | lender["owes"][borrower_name] = net_amount |
| 248 | del lender["owed_by"][borrower_name] |
| 249 | del borrower["owes"][lender_name] |
| 250 | del borrower["owed_by"][lender_name] |
| 251 | elif borrower_owes_lender > lender_owes_borrower: |
| 252 | # borrower owes more to lender (net) |
| 253 | net_amount = borrower_owes_lender - lender_owes_borrower |
| 254 | borrower["owes"][lender_name] = net_amount |
| 255 | del lender["owes"][borrower_name] |
| 256 | del lender["owed_by"][borrower_name] |
| 257 | del borrower["owed_by"][lender_name] |
| 258 | else: |
| 259 | # They owe exactly the same amount - cancel out |
| 260 | del lender["owes"][borrower_name] |
| 261 | del lender["owed_by"][borrower_name] |
| 262 | del borrower["owes"][lender_name] |
| 263 | del borrower["owed_by"][lender_name] |
| 264 | elif lender_owes_borrower > 0: |
| 265 | # Only lender owes borrower - this should not happen in our update logic |
| 266 | pass |
| 267 | elif borrower_owes_lender > 0: |
| 268 | # Only borrower owes lender - this should not happen in our update logic |
| 269 | pass |
| 270 | |
| 271 | # Recalculate balances |
| 272 | self._recalculate_balance(lender) |
| 273 | self._recalculate_balance(borrower) |
| 274 | |
| 275 | # Handled Edge Cases: Invalid URL, Missing payload, Invalid JSON payload, Missing user name, |
| 276 | # User already exists, Missing required fields, Invalid amount type, Negative amount, |
| 277 | # Lender and borrower are the same, Lender or borrower not found, Empty user list in payload, |
| 278 | # User not found |