| 1 | import json |
| 2 | from typing import Dict, Any, List, Optional |
| 3 | |
| 1 | 4 | class RestAPI: |
| 2 | 5 | def __init__(self, database: dict | None = None): |
| 3 | | pass |
| 6 | if database is None: |
| 7 | self.database = {"users": []} |
| 8 | else: |
| 9 | self.database = database |
| 4 | 10 | |
| 5 | 11 | def get(self, url: str, payload: str | None = None) -> str: |
| 6 | | pass |
| 12 | if url == "/users": |
| 13 | if payload is None: |
| 14 | # Return all users sorted by name |
| 15 | users = sorted(self.database["users"], key=lambda x: x["name"]) |
| 16 | return json.dumps({"users": users}) |
| 17 | else: |
| 18 | try: |
| 19 | data = json.loads(payload) |
| 20 | except json.JSONDecodeError: |
| 21 | # Edge Case: Malformed JSON payload |
| 22 | return json.dumps({"error": "Invalid JSON"}) |
| 23 | |
| 24 | if "users" not in data: |
| 25 | # Edge Case: Missing 'users' field in payload |
| 26 | return json.dumps({"error": "Missing users field"}) |
| 27 | |
| 28 | # Filter users by the provided list |
| 29 | requested_names = data["users"] |
| 30 | filtered_users = [user for user in self.database["users"] if user["name"] in requested_names] |
| 31 | # Sort by name |
| 32 | filtered_users.sort(key=lambda x: x["name"]) |
| 33 | return json.dumps({"users": filtered_users}) |
| 34 | else: |
| 35 | # Edge Case: Unknown URL |
| 36 | return json.dumps({"error": "Not found"}) |
| 7 | 37 | |
| 8 | 38 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 39 | if payload is None: |
| 40 | # Edge Case: Missing payload |
| 41 | return json.dumps({"error": "Missing payload"}) |
| 42 | |
| 43 | try: |
| 44 | data = json.loads(payload) |
| 45 | except json.JSONDecodeError: |
| 46 | # Edge Case: Malformed JSON payload |
| 47 | return json.dumps({"error": "Invalid JSON"}) |
| 48 | |
| 49 | if url == "/add": |
| 50 | if "user" not in data: |
| 51 | # Edge Case: Missing 'user' field in payload |
| 52 | return json.dumps({"error": "Missing user field"}) |
| 53 | |
| 54 | new_user_name = data["user"] |
| 55 | |
| 56 | # Check if user already exists |
| 57 | for user in self.database["users"]: |
| 58 | if user["name"] == new_user_name: |
| 59 | # Edge Case: User already exists |
| 60 | return json.dumps(user) |
| 61 | |
| 62 | # Create new user |
| 63 | new_user = { |
| 64 | "name": new_user_name, |
| 65 | "owes": {}, |
| 66 | "owed_by": {}, |
| 67 | "balance": 0.0 |
| 68 | } |
| 69 | self.database["users"].append(new_user) |
| 70 | return json.dumps(new_user) |
| 71 | |
| 72 | elif url == "/iou": |
| 73 | # Validate required fields |
| 74 | required_fields = ["lender", "borrower", "amount"] |
| 75 | for field in required_fields: |
| 76 | if field not in data: |
| 77 | # Edge Case: Missing required field |
| 78 | return json.dumps({"error": f"Missing {field} field"}) |
| 79 | |
| 80 | lender_name = data["lender"] |
| 81 | borrower_name = data["borrower"] |
| 82 | amount = data["amount"] |
| 83 | |
| 84 | # Validate amount |
| 85 | if not isinstance(amount, (int, float)) or amount <= 0: |
| 86 | # Edge Case: Invalid amount (non-positive or non-numeric) |
| 87 | return json.dumps({"error": "Invalid amount"}) |
| 88 | |
| 89 | # Find lender and borrower |
| 90 | lender = None |
| 91 | borrower = None |
| 92 | for user in self.database["users"]: |
| 93 | if user["name"] == lender_name: |
| 94 | lender = user |
| 95 | if user["name"] == borrower_name: |
| 96 | borrower = user |
| 97 | |
| 98 | # Check if lender and borrower exist |
| 99 | if lender is None: |
| 100 | # Edge Case: Lender does not exist |
| 101 | return json.dumps({"error": "Lender does not exist"}) |
| 102 | if borrower is None: |
| 103 | # Edge Case: Borrower does not exist |
| 104 | return json.dumps({"error": "Borrower does not exist"}) |
| 105 | |
| 106 | # Check if lender and borrower are the same |
| 107 | if lender_name == borrower_name: |
| 108 | # Edge Case: Lender and borrower are the same person |
| 109 | return json.dumps({"error": "Lender and borrower cannot be the same"}) |
| 110 | |
| 111 | # Handle debt offsetting first - check if there are existing debts in opposite direction |
| 112 | # Case 1: Lender already owes borrower (reverse debt) |
| 113 | if borrower_name in lender["owes"]: |
| 114 | existing_debt = lender["owes"][borrower_name] |
| 115 | if existing_debt > amount: |
| 116 | # Reduce the existing debt |
| 117 | lender["owes"][borrower_name] -= amount |
| 118 | borrower["owed_by"][lender_name] -= amount |
| 119 | # Update balances |
| 120 | lender["balance"] += amount |
| 121 | borrower["balance"] -= amount |
| 122 | # No new debt created in the forward direction |
| 123 | elif existing_debt == amount: |
| 124 | # Cancel out the debts completely |
| 125 | del lender["owes"][borrower_name] |
| 126 | del borrower["owed_by"][lender_name] |
| 127 | # Update balances |
| 128 | lender["balance"] += amount |
| 129 | borrower["balance"] -= amount |
| 130 | # No new debt created in the forward direction |
| 131 | else: |
| 132 | # Existing debt is less than new IOU, so remove existing debt and create new one |
| 133 | del lender["owes"][borrower_name] |
| 134 | del borrower["owed_by"][lender_name] |
| 135 | # Add the remaining amount to owed_by |
| 136 | remaining = amount - existing_debt |
| 137 | lender["owed_by"][borrower_name] = remaining |
| 138 | borrower["owes"][lender_name] = remaining |
| 139 | # Update balances |
| 140 | lender["balance"] += amount |
| 141 | borrower["balance"] -= amount |
| 142 | # Case 2: Borrower already owes lender (normal debt) |
| 143 | elif lender_name in borrower["owes"]: |
| 144 | existing_debt = borrower["owes"][lender_name] |
| 145 | borrower["owes"][lender_name] += amount |
| 146 | lender["owed_by"][borrower_name] += amount |
| 147 | # Update balances |
| 148 | lender["balance"] += amount |
| 149 | borrower["balance"] -= amount |
| 150 | # Case 3: No existing debt relationship |
| 151 | else: |
| 152 | lender["owed_by"][borrower_name] = amount |
| 153 | borrower["owes"][lender_name] = amount |
| 154 | # Update balances |
| 155 | lender["balance"] += amount |
| 156 | borrower["balance"] -= amount |
| 157 | |
| 158 | # Prepare response with updated users sorted by name |
| 159 | updated_users = [lender, borrower] |
| 160 | updated_users.sort(key=lambda x: x["name"]) |
| 161 | return json.dumps({"users": updated_users}) |
| 162 | else: |
| 163 | # Edge Case: Unknown URL |
| 164 | return json.dumps({"error": "Not found"}) |
| 165 | |
| 166 | def _get_user(self, name: str) -> Optional[Dict[str, Any]]: |
| 167 | """Helper method to get a user by name""" |
| 168 | for user in self.database["users"]: |
| 169 | if user["name"] == name: |
| 170 | return user |
| 171 | return None |