[Blogpost] Modules changed component

ModulesChangedComponent.kt

class ModulesChangedComponent(project: Project) {
  private val rootProject = project.rootProject
  private val rootDirLength = rootProject.projectDir.toString().length + 1
  
  private fun Project.relativePath(): String = this.projectDir.toString().drop(rootDirLength)  
  private fun Project.isTopLevelModule(): Boolean = this.projectDir.listFiles()!!.none { it.name == "build.gradle" }
  
  fun affectedModules(filesChanged: Set<String>): Set<String> {
    val modules = parseModules()
    return modulesChanged(filesChanged, modules)
  }
  
  private fun parseModules(): Set<String> {
    val modules = mutableSetOf("app")
    rootProject.subprojects.forEach {
      if (!it.isTopLevelModule()) {
        modules.add(it.relativePath())
      }
    }
    return modules
  }
  
  private fun modulesChanged(filePaths: Set<String>, filePathPrefixes: Set<String>): Set<String> {
    return filePathPrefixes.mapNotNull { prefix ->
      if (filePaths.any { it.startsWith(prefix) }) {
        prefix
      } else {
        null
      }
    }.toSet()
  }
}