Problem

Acme Analytics stores application logs as a large JSON payload. Write a function that parses the payload and extracts only the events that match a target event type and optional attribute filters.

Given a JSON string representing an object with an events array, return a list of simplified event objects for every valid event whose type matches target_type and whose key-value pairs in required_attrs are all present inside the event's attributes object.

Formal Specification

Implement:

• payload: a JSON string
• target_type: a string
• required_attrs: a dictionary of required attribute filters

Return a list of dictionaries. Each output dictionary must contain:

• id: event id
• timestamp: event timestamp
• user_id: user id if present, otherwise null

Ignore malformed event entries, events missing required top-level fields (id, type, timestamp), and events whose attributes field is not an object.

Examples

Example 1 Input: payload = '{"events":[{"id":"e1","type":"click","timestamp":100,"user":{"id":"u1"},"attributes":{"page":"home"}},{"id":"e2","type":"view","timestamp":101,"attributes":{"page":"home"}}]}', target_type = "click", required_attrs = {"page":"home"} Output: [{"id":"e1","timestamp":100,"user_id":"u1"}]

Example 2 Input: payload = '{"events":[{"id":"e1","type":"click","timestamp":100,"attributes":{"page":"home","device":"mobile"}},{"id":"e2","type":"click","timestamp":101,"attributes":{"page":"home"}}]}', target_type = "click", required_attrs = {"page":"home","device":"mobile"} Output: [{"id":"e1","timestamp":100,"user_id":null}]

Constraints

• 1 <= number of events <= 10^5
• Payload size can be large, so avoid unnecessary extra passes
• Attribute keys and values are JSON-compatible primitives