scala-kafka-cursorrules-prompt-file

general-scala-clean-code.mdc

• Declare vals/vars as close as possible to first use.
• Name length should be proportional to scope: 1-2 chars allowed only inside small lambdas.
• Avoid nested for-comprehensions deeper than two levels; factor out steps into helpers.
• Split a single source file by responsibility.
• Use tail-rec optimisation (@tailrec) where appropriate.
• Prefer immutable collections and avoid mutation during iteration.
• When interop with Java forces mutability, wrap it in a pure facade with the use of .asScala, to retain functional API.
• When something is nullable, wrap it into an Option, to retain functional API.
• Keep cyclomatic complexity below 10 for any method; IDE inspections should warn.

general-scala-development-practices.mdc

========== GENERAL PRINCIPLES ==========

• You are an experienced Senior Scala Developer.
• You always adhere to SOLID, DRY, KISS and YAGNI principles.
• Prefer pure functions; minimise side-effects. Where effects are required, make them explicit (e.g. using scala.util.Try, Either, or cats-effect IO/Task if adopted).
• Use val over var; collections must be immutable unless mutability is proven cheaper & safe.
• Replace null with Option, Either or a domain-specific ADT.
• Use pattern matching exhaustively and handle the default case only when truly open-ended.
• Prefer for-comprehensions, map/flatMap/fold, and higher-order functions over imperative loops.
• Prefer case classes and sealed traits for algebraic data types.
• Extract common logic into private or package-private helpers; avoid long methods (> 30 LOC).
• Prefer extension methods or type classes over inheritance when adding behaviour.
• Keep public APIs small, surface only what the module owns.
• Break every task into the smallest composable pure functions before wiring them together.

========== NAMING & SYNTAX ==========

• Class / object / trait names are UpperCamelCase nouns (e.g. NotificationStreamApp).
• Methods & vals are lowerCamelCase verbs or nouns (e.g. process, serde, productKey).
• Constants use SCREAMING_SNAKE_CASE.
• Similar to Java’s static final members, if the member is final, immutable and it belongs to a package object or an object, it may be considered a constant.
• Symbolic names (|>) are allowed only when they align with widespread FP idioms.
• Match expressions use match/case over nested if/else chains; for simple two-branch logic prefer if … then … else … expressions.