Jessedbrown/scala-critical-path-planner

Scala Critical Path Planner

A real Scala 3 code sample that models a dependency graph, computes a project schedule, surfaces slack, and produces a deterministic representative critical path. The repo also includes a Java entrypoint to show clean JVM interop instead of treating Scala as an isolated language island.

Why this repo is worth looking at

• immutable domain model with explicit error types
• deterministic topological ordering and schedule calculation
• representative critical-path extraction for branching DAGs
• task DSL parser with line-aware validation
• terminal-friendly report formatter
• Java-to-Scala interop through a JVM-safe facade
• automated tests plus GitHub Actions CI

Project layout

• src/main/scala/.../CriticalPathPlanner.scala
  • validates tasks, computes schedule windows, and derives the critical path
• src/main/scala/.../TaskFileParser.scala
  • parses the task DSL into immutable task objects
• src/main/scala/.../ScheduleFormatter.scala
  • renders a readable planning report for terminal use
• src/main/scala/.../Main.scala
  • Scala CLI entrypoint and Java facade
• src/main/java/.../JavaInteropDemo.java
  • Java main class calling back into Scala
• src/test/scala/...
  • schedule, parser, and tie-break tests

Task format

Each non-comment line is:

id | duration | dependency1, dependency2 | owner | risk

Example:

checkout-service | 5 | billing-rules, fraud-signals | platform | 0.50

Run it

scala-cli run . --main-class com.jbrowndevelopment.criticalpath.runPlanner -- --demo
scala-cli run . --main-class com.jbrowndevelopment.criticalpath.runPlanner -- --file examples/release-plan.tasks

Run the Java interop demo

scala-cli run . --main-class com.jbrowndevelopment.criticalpath.JavaInteropDemo

Run the tests

scala-cli test .

Sample output

Project duration: 20
Topological order: design-api -> billing-rules -> fraud-signals -> checkout-service -> schema-migration -> event-backfill -> load-testing -> cutover -> post-launch-audit
Critical path: design-api -> fraud-signals -> checkout-service -> load-testing -> cutover -> post-launch-audit

Why it is a stronger-than-usual Scala sample

This repo is small, but it is not a toy:

• the domain logic is algorithmic rather than CRUD-shaped
• the tests cover both happy-path and graph edge cases
• the Java entrypoint proves the Scala code can live inside a broader JVM codebase

That combination is the actual value proposition for Scala on production teams: concise, high-signal domain code without giving up Java ecosystem interoperability.