Banking System Simulation

# Banking System Simulation You are building an in-memory banking system that is driven by a time-ordered stream of operations. Implement the system so that it processes a list of queries and returns one result per query. Each query is a list of strings. The **first element is the operation name**; the remaining elements are its string arguments. The **second element of every query is a `timestamp`** (an integer number of milliseconds, given in strictly increasing order across the whole input). Amounts are non-negative integers. Account identifiers are arbitrary non-empty strings. Your function receives `queries: List[List[str]]` and must return `List[str]` — the result of each query as a string (use an empty string `""` when an operation is invalid, as defined below). Numbers in the output are rendered without a currency symbol or thousands separators (e.g. `"1500"`). The system is leveled: implement the levels in order. Each higher level adds operations; earlier operations keep working unchanged. ## Level 1 — Accounts and balances - `["CREATE_ACCOUNT", timestamp, account_id]` → `"true"` if a new account is created; `"false"` if an account with that id already exists. - `["DEPOSIT", timestamp, account_id, amount]` → the account's new balance as a string. If the account does not exist, return `""`. - `["GET_BALANCE", timestamp, account_id]` → the account's current balance. If the account does not exist (or no longer exists), return `""`. ## Level 2 — Transfers and spending ranks - `["TRANSFER", timestamp, source_id, target_id, amount]` → the source account's resulting balance. Return `""` if either account is missing, if `source_id == target_id`, or if the source has insufficient funds (no transfer happens in that case). - `["TOP_SPENDERS", timestamp, n]` → the top `n` accounts ranked by **total outgoing amount** (the sum of all `TRANSFER` amounts they sent plus all `PAY` amounts, see Level 3), as a comma-and-space separated string: `"id1(total1), id2(total2)"`. Rank highest total first; break ties by account id in ascending lexicographic order. Include every existing account; if fewer than `n` accounts exist, return all of them. ## Level 3 — Payments with deferred cashback - `["PAY", timestamp, account_id, amount]` → debits `amount` immediately and returns a new payment id of the form `"payment1"`, `"payment2"`, … (a single global counter, incremented on every successful `PAY`). Return `""` if the account is missing or has insufficient funds. Each payment earns **2% cashback** (`floor(amount * 2 / 100)`) that is credited back to the same account **exactly `86400000` ms (24 hours) after** the payment timestamp. - `["GET_PAYMENT_STATUS", timestamp, account_id, payment]` → `"IN_PROGRESS"` if the cashback has not yet been credited at `timestamp`, `"CASHBACK_RECEIVED"` if it has. Return `""` if the account does not exist or the payment id does not belong to that account. Cashback that is due must be settled (added to the balance) **before** evaluating any operation whose timestamp is at or after the cashback time. In other words, every operation should first apply all pending cashbacks whose credit time is `<= timestamp`. ## Level 4 — Account merge - `["MERGE_ACCOUNTS", timestamp, account_id_1, account_id_2]` → `"true"` on success, `"false"` if either account is missing or `account_id_1 == account_id_2`. Merging folds `account_id_2` into `account_id_1`: balances are summed, outgoing-total histories are summed, and any of account 2's pending cashbacks are redirected to account 1. After the merge, `account_id_2` no longer exists, but a `GET_PAYMENT_STATUS` query for a payment originally made by account 2 must still succeed when issued against `account_id_1`. ## Constraints - `1 <= len(queries) <= 10^4`. - Timestamps are strictly increasing integers in `[1, 10^15]`. - Amounts are integers in `[0, 10^9]`. - All outputs are strings. ## Example Input: ``` [ ["CREATE_ACCOUNT", "1", "alice"], ["CREATE_ACCOUNT", "2", "bob"], ["DEPOSIT", "3", "alice", "2000"], ["TRANSFER", "4", "alice", "bob", "500"], ["TOP_SPENDERS", "5", "2"], ["PAY", "6", "alice", "1000"], ["GET_PAYMENT_STATUS", "7", "alice", "payment1"], ["GET_PAYMENT_STATUS", "86400007", "alice", "payment1"], ["GET_BALANCE", "86400008", "alice"] ] ``` Output: ``` ["true", "true", "2000", "1500", "alice(500), bob(0)", "payment1", "IN_PROGRESS", "CASHBACK_RECEIVED", "520"] ``` Explanation of the last two lines: alice paid 1000 at t=6, leaving 500. At t=86400006 (24h later) the 2% cashback of 20 is credited, so by t=86400008 her balance is `500 + 20 = 520`.