Core Requirements

• Multiple topics: Each topic is created with a fixed number of partitions.
• Multiple producers: Producers can publish messages to any topic partition.
• Multiple consumers: Multiple consumers can read messages. Each consumer maintains its own read position.
• Ordering guarantee: Messages must be delivered in the same order they were published within a partition.

Topic

• A topic has a unique name and a fixed partitionCount.
• Topics are independent from each other.

Partition

• Each topic has partitions numbered from 0 to partitionCount - 1.
• Each partition is an append-only log of messages.
• Each published message is assigned a monotonically increasing offset within its partition, starting at 0.

Consumer Cursor

• For each (topicName, consumerId, partitionId), the service stores the next offset the consumer should read.
• Different consumerId values are independent and can read the same partition from the beginning.

Ordering Guarantees

• Publish order: If two messages are published to the same (topicName, partitionId), their assigned offsets must reflect the publish order.
• Consume order: A consumer must receive messages from a partition strictly in increasing offset order.
• If no new messages exist at the consumer's cursor, consume(...) will return empty list.

Method Signatures

1) Create a Topic

• Creates a new topic with partitionCount partitions.
• Returns true if the topic was created, returns false if topicName already exists.
• partitionCount ≥ 1

2) Publish a Message

• Appends message to the specified partition of the topic.
• Returns a message identifier in the form "p<partitionId>:<offset>" (for example, "p0:12").
• 0 ≤ partitionId < partitionCount(topicName)

3) Consume Messages

• Returns up to maxMessages messages from the consumer's current cursor for that partition.
• If messages are available, returns immediately with up to maxMessages in partition order.
• If no messages are available then returns an empty list.
• maxMessages ≥ 1
• Consumer cursor advances only for that (topicName, consumerId, partitionId).

Constraints

• 1 ≤ partitionCount ≤ 100
• 1 ≤ topicName.length() ≤ 100
• topicName is non-empty and should be treated as case-sensitive.
• 1 ≤ message.length() ≤ 10_000
• 1 ≤ maxMessages ≤ 10_000
• Assume the service is in-memory only (no persistence required).
• Ordering is required only within a partition, no ordering is required across different partitions.

Examples

Example 1: Basic Topic Creation, Publish, and Consume

Example 2: Multiple Consumers Have Independent Cursors

Example 3: maxMessages Limits the Returned Batch Size