package snake

import java.nio.file.{Files, Path, Paths}
import scala.jdk.CollectionConverters.*

class PuritySuite extends munit.FunSuite:
  private val srcDir = Paths.get(sys.props.getOrElse("user.dir", ".")).resolve("src")

  // Files that are allowed to touch the outside world (a future web/ directory lives outside src/).
  private def excluded(file: Path): Boolean = file.getFileName.toString == "Runtime.scala"

  private val banned: List[(String, scala.util.matching.Regex, String)] = List(
    ("var", """\bvar\b""".r, "var n = 0"),
    ("mutable", """\bmutable\b""".r, "val b = scala.collection.mutable.ListBuffer[Int]()"),
    ("while", """\bwhile\b""".r, "while n < 3 do n += 1"),
    ("scala.util.Random", """\bscala\.util\.Random\b""".r, "val r = scala.util.Random.nextInt()"),
    ("System.", """\bSystem\.""".r, "val t = System.currentTimeMillis()"),
    ("println", """\bprintln\b""".r, "println(\"hi\")")
  )

  private def stripComments(code: String): String =
    code.replaceAll("""(?s)/\*.*?\*/""", "").replaceAll("""(?m)//.*$""", "")

  private def violations(code: String): List[String] =
    val clean = stripComments(code)
    banned.collect { case (name, re, _) if re.findFirstIn(clean).isDefined => name }

  private def scalaFiles(dir: Path): List[Path] =
    if !Files.exists(dir) then Nil
    else Files.walk(dir).iterator.asScala.filter(f => f.toString.endsWith(".scala")).toList.sorted

  banned.foreach { (name, _, sample) =>
    test(s"purity scanner flags a known-bad sample using $name") {
      assert(violations(sample).contains(name))
    }
  }

  test("purity scanner ignores banned words inside comments") {
    val code = "// var mutable println\n/* while (x) System.exit(1) */\nval a = 1 // scala.util.Random\n"
    assertEquals(violations(code), Nil)
  }

  test("purity scanner accepts ordinary pure code") {
    assertEquals(violations("def f(xs: List[Int]): List[Int] = xs.map(_ + 1)"), Nil)
  }

  scalaFiles(srcDir).filterNot(excluded).foreach { f =>
    test(s"purity: ${srcDir.relativize(f)} has no banned constructs") {
      assertEquals(violations(Files.readString(f)), Nil)
    }
  }