Prepare for Backend Parsing, API Integration, AI Coding, and Bug Fixing Rounds

Payment Event Stream Processor

At payment platforms like Stripe, ingestion pipelines often receive high-volume streams of semi-structured event logs from external partner rails. These events must be parsed, validated, and applied against an account balance while respecting idempotency and lifecycle constraints.

Implement a function process_payment_events(events: list[str]) -> dict that parses a sequence of payment action records, validates each record against business rules, and returns the processing results.

Record Format

Each string in events follows the format: ACTION|idempotency_key=;amount=;currency=;charge_id=

• Supported actions: AUTHORIZE, CAPTURE, REFUND.
• Key-value attributes are separated by semicolons (;).
• Key-value pairs may appear in any order.
• AUTHORIZE: Requires idempotency_key, amount, and currency. Generates a unique internal charge_id represented by ch_. Sets the initial authorized balance.
• CAPTURE: Requires idempotency_key, charge_id, and amount. Captures up to the remaining authorized amount for that charge. Captured funds increase the merchant's settled balance.
• REFUND: Requires idempotency_key, charge_id, and amount. Refunds up to the total captured amount for that charge. Refunded funds decrease the settled balance.

Business & Idempotency Rules

1. Malformed Syntax: If a string lacks the pipe separator, has unknown actions, has missing mandatory fields, or contains a non-integer or non-positive amount (amount <= 0), reject the record with reason "MALFORMED".
2. Idempotency:
   • If an idempotency_key is reused with identical parameters, return the identical previous outcome without re-applying financial mutations ("DUPLICATE").
   • If an idempotency_key is reused with different parameters, reject it with reason "IDEMPOTENCY_CONFLICT".
3. State Invariants:
   • CAPTURE cannot capture more than the currently uncaptured authorized balance.
   • REFUND cannot refund more than the currently captured, unrefunded balance.
   • Any reference to an unknown or unauthorized charge_id must be rejected with reason "INVALID_CHARGE".
   • Over-capturing or over-refunding must be rejected with reason "INSUFFICIENT_FUNDS".

Interface

def process_payment_events(events: list[str]) -> dict:
    pass

Output Format

Return a dictionary with two keys:

• "settled_balances": A dictionary mapping currency (e.g., "USD") to the total settled amount (integer cents).
• "results": A list of strings, one per input event: "SUCCESS", "DUPLICATE", or "ERROR: ".

Example

events = [
    "AUTHORIZE|idempotency_key=k1;amount=1000;currency=usd",
    "CAPTURE|idempotency_key=k2;charge_id=ch_k1;amount=600",
    "CAPTURE|idempotency_key=k2;charge_id=ch_k1;amount=600",
    "REFUND|idempotency_key=k3;charge_id=ch_k1;amount=700",
    "REFUND|idempotency_key=k4;charge_id=ch_k1;amount=400"
]

result = process_payment_events(events)
# result == {
#     "settled_balances": {"usd": 200},
#     "results": [
#         "SUCCESS",
#         "SUCCESS",
#         "DUPLICATE",
#         "ERROR: INSUFFICIENT_FUNDS",
#         "SUCCESS"
#     ]
# }

Constraints

• 1 <= len(events) <= 10000
• 1 <= amount <= 10^9
• Currencies are case-insensitive and should be normalized to lowercase.