| 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 supported. |
| 30 | """ |
| 31 | if url == "/users": |
| 32 | if payload is None: |
| 33 | # Return all users |
| 34 | users = [self._create_user_object(user) for user in self.database["users"]] |
| 35 | return json.dumps({"users": users}) |
| 36 | else: |
| 37 | # Return specific users |
| 38 | payload_data = json.loads(payload) |
| 39 | user_names = payload_data.get("users", []) |
| 40 | |
| 41 | # Edge Case: Empty user list in payload |
| 42 | if not user_names: |
| 43 | return json.dumps({"users": []}) |
| 44 | |
| 45 | # Edge Case: Non-existent users in payload |
| 46 | result_users = [] |
| 47 | for user_name in user_names: |
| 48 | user = self._find_user(user_name) |
| 49 | if user: |
| 50 | result_users.append(self._create_user_object(user)) |
| 51 | |
| 52 | # Sort by name |
| 53 | result_users.sort(key=lambda u: u["name"]) |
| 54 | return json.dumps({"users": result_users}) |
| 55 | else: |
| 56 | # Edge Case: Unsupported URL |
| 57 | raise ValueError(f"Unsupported URL: {url}") |
| 58 | |
| 8 | 59 | def post(self, url: str, payload: str | None = None) -> str: |
| 9 | | pass |
| 60 | """ |
| 61 | Handle POST requests to the API. |
| 62 | |
| 63 | Args: |
| 64 | url: The endpoint URL. |
| 65 | payload: JSON payload. |
| 66 | |
| 67 | Returns: |
| 68 | JSON string response. |
| 69 | |
| 70 | Raises: |
| 71 | ValueError: If the URL is not supported or if required data is missing. |
| 72 | """ |
| 73 | if payload is None: |
| 74 | # Edge Case: Missing payload |
| 75 | raise ValueError("Payload is required for POST requests") |
| 76 | |
| 77 | payload_data = json.loads(payload) |
| 78 | |
| 79 | if url == "/add": |
| 80 | user_name = payload_data.get("user") |
| 81 | |
| 82 | # Edge Case: Missing user name |
| 83 | if not user_name: |
| 84 | raise ValueError("User name is required") |
| 85 | |
| 86 | # Edge Case: User already exists |
| 87 | if self._find_user(user_name): |
| 88 | raise ValueError(f"User {user_name} already exists") |
| 89 | |
| 90 | new_user = { |
| 91 | "name": user_name, |
| 92 | "owes": {}, |
| 93 | "owed_by": {}, |
| 94 | "balance": 0.0 |
| 95 | } |
| 96 | self.database["users"].append(new_user) |
| 97 | return json.dumps(self._create_user_object(new_user)) |
| 98 | |
| 99 | elif url == "/iou": |
| 100 | lender_name = payload_data.get("lender") |
| 101 | borrower_name = payload_data.get("borrower") |
| 102 | amount = payload_data.get("amount") |
| 103 | |
| 104 | # Edge Case: Missing required fields |
| 105 | if not lender_name or not borrower_name or amount is None: |
| 106 | raise ValueError("Lender, borrower, and amount are required") |
| 107 | |
| 108 | # Edge Case: Negative amount |
| 109 | if amount < 0: |
| 110 | raise ValueError("Amount must be non-negative") |
| 111 | |
| 112 | # Edge Case: Lender and borrower are the same |
| 113 | if lender_name == borrower_name: |
| 114 | raise ValueError("Lender and borrower cannot be the same person") |
| 115 | |
| 116 | lender = self._find_user(lender_name) |
| 117 | borrower = self._find_user(borrower_name) |
| 118 | |
| 119 | # Edge Case: Non-existent lender or borrower |
| 120 | if not lender: |
| 121 | raise ValueError(f"User {lender_name} does not exist") |
| 122 | if not borrower: |
| 123 | raise ValueError(f"User {borrower_name} does not exist") |
| 124 | |
| 125 | # Handle debt offsetting |
| 126 | # If lender owes borrower money, reduce that debt first |
| 127 | if borrower_name in lender["owes"]: |
| 128 | existing_debt = lender["owes"][borrower_name] |
| 129 | if amount > existing_debt: |
| 130 | # Remove the existing debt and create new owed amount |
| 131 | del lender["owes"][borrower_name] |
| 132 | del borrower["owed_by"][lender_name] |
| 133 | |
| 134 | # Add the remaining amount to owed_by |
| 135 | new_amount = amount - existing_debt |
| 136 | lender["owed_by"][borrower_name] = new_amount |
| 137 | borrower["owes"][lender_name] = new_amount |
| 138 | elif amount == existing_debt: |
| 139 | # Exactly offset the debt |
| 140 | del lender["owes"][borrower_name] |
| 141 | del borrower["owed_by"][lender_name] |
| 142 | else: |
| 143 | # Reduce the existing debt |
| 144 | lender["owes"][borrower_name] -= amount |
| 145 | borrower["owed_by"][lender_name] -= amount |
| 146 | else: |
| 147 | # No existing debt from lender to borrower |
| 148 | # Update lender's owed_by |
| 149 | if borrower_name in lender["owed_by"]: |
| 150 | lender["owed_by"][borrower_name] += amount |
| 151 | else: |
| 152 | lender["owed_by"][borrower_name] = amount |
| 153 | |
| 154 | # Update borrower's owes |
| 155 | if lender_name in borrower["owes"]: |
| 156 | borrower["owes"][lender_name] += amount |
| 157 | else: |
| 158 | borrower["owes"][lender_name] = amount |
| 159 | |
| 160 | # Recalculate balances from scratch |
| 161 | lender_total_owed_by = sum(lender["owed_by"].values()) |
| 162 | lender_total_owes = sum(lender["owes"].values()) |
| 163 | lender["balance"] = lender_total_owed_by - lender_total_owes |
| 164 | |
| 165 | borrower_total_owed_by = sum(borrower["owed_by"].values()) |
| 166 | borrower_total_owes = sum(borrower["owes"].values()) |
| 167 | borrower["balance"] = borrower_total_owed_by - borrower_total_owes |
| 168 | |
| 169 | # Return updated users |
| 170 | users = [self._create_user_object(lender), self._create_user_object(borrower)] |
| 171 | users.sort(key=lambda u: u["name"]) |
| 172 | return json.dumps({"users": users}) |
| 173 | else: |
| 174 | # Edge Case: Unsupported URL |
| 175 | raise ValueError(f"Unsupported URL: {url}") |
| 176 | |
| 177 | def _find_user(self, name: str) -> Optional[Dict]: |
| 178 | """ |
| 179 | Find a user by name in the database. |
| 180 | |
| 181 | Args: |
| 182 | name: The name of the user to find. |
| 183 | |
| 184 | Returns: |
| 185 | The user dictionary if found, None otherwise. |
| 186 | """ |
| 187 | for user in self.database["users"]: |
| 188 | if user["name"] == name: |
| 189 | return user |
| 190 | return None |
| 191 | |
| 192 | def _create_user_object(self, user: Dict) -> Dict: |
| 193 | """ |
| 194 | Create a user object for API response. |
| 195 | |
| 196 | Args: |
| 197 | user: The user dictionary from the database. |
| 198 | |
| 199 | Returns: |
| 200 | A user object formatted for API response. |
| 201 | """ |
| 202 | # Calculate balance from owes and owed_by |
| 203 | total_owed_by = sum(user["owed_by"].values()) |
| 204 | total_owes = sum(user["owes"].values()) |
| 205 | balance = total_owed_by - total_owes |
| 206 | |
| 207 | return { |
| 208 | "name": user["name"], |
| 209 | "owes": user["owes"], |
| 210 | "owed_by": user["owed_by"], |
| 211 | "balance": balance |
| 212 | } |
| 213 | |
| 214 | # Handled Edge Cases: Unsupported URL, Missing payload, Missing user name, User already exists, Missing required fields, Negative amount, Lender and borrower are the same, Non-existent lender or borrower, Empty user list in payload, Non-existent users in payload |