| 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 | 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 response string. |
| 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 users list in payload |
| 38 | if not user_names: |
| 39 | return json.dumps({"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: Requested user does not exist |
| 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 response string. |
| 64 | """ |
| 65 | if payload is None: |
| 66 | # Edge Case: Missing payload |
| 67 | return json.dumps({"error": "Missing payload"}) |
| 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 payload"}) |
| 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": "Missing user name"}) |
| 81 | |
| 82 | # Edge Case: User already exists |
| 83 | if any(user["name"] == user_name for user in self.database["users"]): |
| 84 | return json.dumps({"error": "User already exists"}) |
| 85 | |
| 86 | new_user = { |
| 87 | "name": user_name, |
| 88 | "owes": {}, |
| 89 | "owed_by": {}, |
| 90 | "balance": 0.0 |
| 91 | } |
| 92 | |
| 93 | self.database["users"].append(new_user) |
| 94 | return json.dumps(self._format_user(new_user)) |
| 95 | |
| 96 | elif url == "/iou": |
| 97 | lender_name = data.get("lender") |
| 98 | borrower_name = data.get("borrower") |
| 99 | amount = data.get("amount") |
| 100 | |
| 101 | # Edge Case: Missing required fields |
| 102 | if not lender_name or not borrower_name or amount is None: |
| 103 | return json.dumps({"error": "Missing required fields"}) |
| 104 | |
| 105 | # Edge Case: Invalid amount type |
| 106 | if not isinstance(amount, (int, float)): |
| 107 | return json.dumps({"error": "Invalid amount"}) |
| 108 | |
| 109 | # Edge Case: Negative amount |
| 110 | if amount < 0: |
| 111 | return json.dumps({"error": "Amount must be positive"}) |
| 112 | |
| 113 | # Edge Case: Lender and borrower are the same |
| 114 | if lender_name == borrower_name: |
| 115 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 116 | |
| 117 | lender = next((user for user in self.database["users"] if user["name"] == lender_name), None) |
| 118 | borrower = next((user for user in self.database["users"] if user["name"] == borrower_name), None) |
| 119 | |
| 120 | # Edge Case: Lender or borrower does not exist |
| 121 | if not lender or not borrower: |
| 122 | return json.dumps({"error": "Lender or borrower does not exist"}) |
| 123 | |
| 124 | # Handle debt offsetting when lender already owes borrower |
| 125 | if lender_name in borrower["owed_by"] and borrower_name in lender["owes"]: |
| 126 | # Lender owes borrower, and now lender is lending to borrower |
| 127 | existing_debt = lender["owes"][borrower_name] |
| 128 | |
| 129 | if amount == existing_debt: |
| 130 | # Debts cancel out completely |
| 131 | del lender["owes"][borrower_name] |
| 132 | del borrower["owed_by"][lender_name] |
| 133 | elif amount > existing_debt: |
| 134 | # New loan is larger, so borrower now owes lender the difference |
| 135 | del lender["owes"][borrower_name] |
| 136 | del borrower["owed_by"][lender_name] |
| 137 | |
| 138 | # Create new debt in opposite direction |
| 139 | lender["owed_by"][borrower_name] = amount - existing_debt |
| 140 | borrower["owes"][lender_name] = amount - existing_debt |
| 141 | else: |
| 142 | # New loan is smaller, reduce existing debt |
| 143 | lender["owes"][borrower_name] = existing_debt - amount |
| 144 | borrower["owed_by"][lender_name] = existing_debt - amount |
| 145 | else: |
| 146 | # Normal case: no existing opposite debt |
| 147 | # Update lender's owed_by |
| 148 | if borrower_name in lender["owed_by"]: |
| 149 | lender["owed_by"][borrower_name] += amount |
| 150 | else: |
| 151 | lender["owed_by"][borrower_name] = amount |
| 152 | |
| 153 | # Update borrower's owes |
| 154 | if lender_name in borrower["owes"]: |
| 155 | borrower["owes"][lender_name] += amount |
| 156 | else: |
| 157 | borrower["owes"][lender_name] = amount |
| 158 | |
| 159 | # Recalculate balances |
| 160 | self._recalculate_balance(lender) |
| 161 | self._recalculate_balance(borrower) |
| 162 | |
| 163 | # Return updated users sorted by name |
| 164 | users = [lender, borrower] |
| 165 | users.sort(key=lambda x: x["name"]) |
| 166 | |
| 167 | return json.dumps({"users": [self._format_user(user) for user in users]}) |
| 168 | |
| 169 | # Edge Case: Invalid URL |
| 170 | return json.dumps({"error": "Invalid URL"}) |
| 171 | |
| 172 | def _format_user(self, user: Dict[str, Any]) -> Dict[str, Any]: |
| 173 | """ |
| 174 | Format a user object for output. |
| 175 | |
| 176 | Args: |
| 177 | user: The user dictionary. |
| 178 | |
| 179 | Returns: |
| 180 | Formatted user dictionary. |
| 181 | """ |
| 182 | # Create a copy to avoid modifying the original |
| 183 | formatted = { |
| 184 | "name": user["name"], |
| 185 | "owes": user["owes"].copy(), |
| 186 | "owed_by": user["owed_by"].copy(), |
| 187 | "balance": user["balance"] |
| 188 | } |
| 189 | |
| 190 | # Remove empty entries |
| 191 | formatted["owes"] = {k: v for k, v in formatted["owes"].items() if v != 0} |
| 192 | formatted["owed_by"] = {k: v for k, v in formatted["owed_by"].items() if v != 0} |
| 193 | |
| 194 | return formatted |
| 195 | |
| 196 | def _recalculate_balance(self, user: Dict[str, Any]) -> None: |
| 197 | """ |
| 198 | Recalculate the balance for a user. |
| 199 | |
| 200 | Args: |
| 201 | user: The user dictionary. |
| 202 | """ |
| 203 | total_owed_by = sum(user["owed_by"].values()) |
| 204 | total_owes = sum(user["owes"].values()) |
| 205 | user["balance"] = round(total_owed_by - total_owes, 2) |
| 206 | |
| 207 | # Handled Edge Cases: Invalid URL, Missing payload, Invalid JSON payload, Missing user name, |
| 208 | # User already exists, Missing required fields, Invalid amount type, Negative amount, |
| 209 | # Lender and borrower are the same, Lender or borrower does not exist, Empty users list in payload, |
| 210 | # Requested user does not exist |