| 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 string response. |
| 27 | |
| 28 | Raises: |
| 29 | ValueError: If the URL is not recognized. |
| 30 | """ |
| 31 | if url == "/users": |
| 32 | if payload is None: |
| 33 | # Return all users sorted by name |
| 34 | users = sorted(self.database["users"], key=lambda x: x["name"]) |
| 35 | return json.dumps({"users": users}) |
| 36 | else: |
| 37 | # Return only specified users sorted by name |
| 38 | payload_data = json.loads(payload) |
| 39 | requested_users = payload_data.get("users", []) |
| 40 | |
| 41 | # Edge Case: Handle when users list is empty |
| 42 | if not requested_users: |
| 43 | return json.dumps({"users": []}) |
| 44 | |
| 45 | # Filter users |
| 46 | result_users = [user for user in self.database["users"] if user["name"] in requested_users] |
| 47 | # Sort by name |
| 48 | result_users = sorted(result_users, key=lambda x: x["name"]) |
| 49 | return json.dumps({"users": result_users}) |
| 50 | else: |
| 51 | raise ValueError(f"Unknown URL: {url}") |
| 52 | |
| 8 | 53 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 54 | """ |
| 55 | Handle POST requests to the API. |
| 56 | |
| 57 | Args: |
| 58 | url: The endpoint URL. |
| 59 | payload: JSON payload. |
| 60 | |
| 61 | Returns: |
| 62 | JSON string response. |
| 63 | |
| 64 | Raises: |
| 65 | ValueError: If the URL is not recognized or if there are validation errors. |
| 66 | """ |
| 67 | if url == "/add": |
| 68 | if payload is None: |
| 69 | raise ValueError("Payload required for /add endpoint") |
| 70 | |
| 71 | payload_data = json.loads(payload) |
| 72 | new_user_name = payload_data.get("user") |
| 73 | |
| 74 | # Edge Case: Handle missing user field |
| 75 | if new_user_name is None: |
| 76 | raise ValueError("User field is required") |
| 77 | |
| 78 | # Edge Case: Handle duplicate user |
| 79 | for user in self.database["users"]: |
| 80 | if user["name"] == new_user_name: |
| 81 | raise ValueError(f"User {new_user_name} already exists") |
| 82 | |
| 83 | # Create new user |
| 84 | new_user = { |
| 85 | "name": new_user_name, |
| 86 | "owes": {}, |
| 87 | "owed_by": {}, |
| 88 | "balance": 0.0 |
| 89 | } |
| 90 | |
| 91 | self.database["users"].append(new_user) |
| 92 | |
| 93 | # Sort users by name |
| 94 | self.database["users"] = sorted(self.database["users"], key=lambda x: x["name"]) |
| 95 | |
| 96 | return json.dumps(new_user) |
| 97 | |
| 98 | elif url == "/iou": |
| 99 | if payload is None: |
| 100 | raise ValueError("Payload required for /iou endpoint") |
| 101 | |
| 102 | payload_data = json.loads(payload) |
| 103 | lender_name = payload_data.get("lender") |
| 104 | borrower_name = payload_data.get("borrower") |
| 105 | amount = payload_data.get("amount") |
| 106 | |
| 107 | # Edge Case: Handle missing fields |
| 108 | if lender_name is None or borrower_name is None or amount is None: |
| 109 | raise ValueError("Lender, borrower, and amount fields are required") |
| 110 | |
| 111 | # Edge Case: Handle lender and borrower being the same person |
| 112 | if lender_name == borrower_name: |
| 113 | raise ValueError("Lender and borrower cannot be the same person") |
| 114 | |
| 115 | # Edge Case: Handle negative amount |
| 116 | if amount < 0: |
| 117 | raise ValueError("Amount must be non-negative") |
| 118 | |
| 119 | # Find lender and borrower |
| 120 | lender = None |
| 121 | borrower = None |
| 122 | |
| 123 | for user in self.database["users"]: |
| 124 | if user["name"] == lender_name: |
| 125 | lender = user |
| 126 | elif user["name"] == borrower_name: |
| 127 | borrower = user |
| 128 | |
| 129 | # Edge Case: Handle unknown lender or borrower |
| 130 | if lender is None: |
| 131 | raise ValueError(f"User {lender_name} does not exist") |
| 132 | if borrower is None: |
| 133 | raise ValueError(f"User {borrower_name} does not exist") |
| 134 | |
| 135 | # Update owes and owed_by with proper netting logic |
| 136 | # Check if lender already owes money to borrower |
| 137 | existing_lender_owes_borrower = lender["owes"].get(borrower_name, 0) |
| 138 | |
| 139 | if existing_lender_owes_borrower > 0: |
| 140 | # Lender owes borrower money, so we need to net the amounts |
| 141 | if amount == existing_lender_owes_borrower: |
| 142 | # Exact cancellation - remove all entries (net zero) |
| 143 | del lender["owes"][borrower_name] |
| 144 | del borrower["owed_by"][lender_name] |
| 145 | elif amount > existing_lender_owes_borrower: |
| 146 | # New loan is larger - borrower now owes lender the difference |
| 147 | del lender["owes"][borrower_name] |
| 148 | del borrower["owed_by"][lender_name] |
| 149 | |
| 150 | difference = amount - existing_lender_owes_borrower |
| 151 | lender["owed_by"][borrower_name] = difference |
| 152 | borrower["owes"][lender_name] = difference |
| 153 | else: |
| 154 | # Existing debt is larger - reduce the amount lender owes |
| 155 | new_amount = existing_lender_owes_borrower - amount |
| 156 | lender["owes"][borrower_name] = new_amount |
| 157 | borrower["owed_by"][lender_name] = new_amount |
| 158 | else: |
| 159 | # No existing debt from lender to borrower, just add the new IOU |
| 160 | # For lender: add borrower to owed_by |
| 161 | if borrower_name in lender["owed_by"]: |
| 162 | lender["owed_by"][borrower_name] += amount |
| 163 | else: |
| 164 | lender["owed_by"][borrower_name] = amount |
| 165 | |
| 166 | # For borrower: add lender to owes |
| 167 | if lender_name in borrower["owes"]: |
| 168 | borrower["owes"][lender_name] += amount |
| 169 | else: |
| 170 | borrower["owes"][lender_name] = amount |
| 171 | |
| 172 | # Recalculate balances |
| 173 | lender_total_owed = sum(lender["owed_by"].values()) |
| 174 | lender_total_owes = sum(lender["owes"].values()) |
| 175 | lender["balance"] = lender_total_owed - lender_total_owes |
| 176 | |
| 177 | borrower_total_owed = sum(borrower["owed_by"].values()) |
| 178 | borrower_total_owes = sum(borrower["owes"].values()) |
| 179 | borrower["balance"] = borrower_total_owed - borrower_total_owes |
| 180 | |
| 181 | |
| 182 | |
| 183 | # Return updated users sorted by name |
| 184 | result_users = sorted([lender, borrower], key=lambda x: x["name"]) |
| 185 | return json.dumps({"users": result_users}) |
| 186 | |
| 187 | else: |
| 188 | raise ValueError(f"Unknown URL: {url}") |
| 189 | |
| 190 | # Handled Edge Cases: Missing payload for /add, missing user field, duplicate user, |
| 191 | # missing fields for /iou, lender and borrower being the same, |
| 192 | # negative amount, unknown lender or borrower, zero balances |