TooLarge.scala

import scalafix.Diagnostic
import scalafix.Patch
import scalafix.lint.LintSeverity
import scalafix.v1.SyntacticDocument
import scalafix.v1.SyntacticRule
import scala.meta.Defn
import scala.meta.Tree
import scala.meta.inputs.Input
import scala.meta.inputs.Position

class TooLarge extends SyntacticRule("TooLarge") {

  private def classLimit = 500

  private val treeToLimit: PartialFunction[Tree, (Int, String)] = {
    case _: Defn.Def    => (100, "method")
    case _: Defn.Trait  => (classLimit, "trait")
    case _: Defn.Object => (classLimit, "object")
    case _: Defn.Class  => (classLimit, "class")
  }

  private val pf: PartialFunction[Tree, Patch] = Function.unlift { (t: Tree) =>
    treeToLimit.lift.apply(t).map {
      case (limit, name) =>
        val size = t.pos.endLine - t.pos.startLine
        if (limit < size) {
          Patch.lint(TooLargeWarn(position = t.pos, name = name, size = size))
        } else {
          Patch.empty
        }
    }
  }

  override def fix(implicit doc: SyntacticDocument): Patch = {
    val scalaSourcePathOpt = PartialFunction.condOpt(doc.input) {
      case f: Input.VirtualFile =>
        f.path
      case f: Input.File =>
        f.path.toString
    }
    // TODO support Windows
    if (!scala.util.Properties.isWin && scalaSourcePathOpt.exists(_.contains("/src/main/"))) {
      doc.tree.collect(pf).asPatch
    } else {
      Patch.empty
    }
  }
}

case class TooLargeWarn(override val position: Position, name: String, size: Int) extends Diagnostic {
  override def message  = s"${name} is too large! ${size}"
  override def severity = LintSeverity.Warning
}