package wacc

import scala.collection.mutable
import cats.data.{Chain, NonEmptyList}
import parsley.{Failure, Success}

import java.nio.file.{Files, Path}
import cats.syntax.all._

import cats.effect.IO
import cats.effect.ExitCode

import com.monovore.decline._
import com.monovore.decline.effect._
import com.monovore.decline.Argument

import org.typelevel.log4cats.slf4j.Slf4jLogger
import org.typelevel.log4cats.Logger

import assemblyIR as asm
import cats.data.ValidatedNel

/*
TODO:
  1) IO correctness
  2) Errors can be handled more gracefully - currently, parallelised compilation is not fail fast as far as I am aware
  3) splitting the file up and nicer refactoring
  4) logging could be removed
  5) general cleanup and comments (things like replacing home/<user> with ~ , and names of parameters and args, descriptions etc)
 */

given logger: Logger[IO] = Slf4jLogger.getLogger[IO]

val logOpt: Opts[Boolean] =
  Opts.flag("log", "Enable logging for additional compilation details", short = "l").orFalse

def validateFile(path: Path): ValidatedNel[String, Path] = {
  (for {
    // TODO: redundant 2nd parameter :(
    _ <- Either.cond(Files.exists(path), (), s"File '${path}' does not exist")
    _ <- Either.cond(Files.isRegularFile(path), (), s"File '${path}' must be a regular file")
    _ <- Either.cond(path.toString.endsWith(".wacc"), (), "File must have .wacc extension")
  } yield path).toValidatedNel
}

val filesOpt: Opts[NonEmptyList[Path]] =
  Opts.arguments[Path]("files").mapValidated {
    _.traverse(validateFile)
  }

val outputOpt: Opts[Option[Path]] =
  Opts
    .option[Path]("output", metavar = "path", help = "Output directory for compiled files.")
    .orNone

val greedyOpt: Opts[Boolean] =
  Opts.flag("greedy", "Compile WACC files sequentially instead of parallelly", short = "g").orFalse

def frontend(
    contents: String
): IO[Either[Int, microWacc.Program]] = {
  IO(parser.parse(contents)).flatMap {
    case Failure(msg) =>
      logger.error(s"Syntax error: $msg").as(Left(100))

    case Success(prog) =>
      given errors: mutable.Builder[Error, List[Error]] = List.newBuilder

      val (names, funcs) = renamer.rename(prog)
      given ctx: typeChecker.TypeCheckerCtx = typeChecker.TypeCheckerCtx(names, funcs, errors)

      val typedProg = typeChecker.check(prog)

      val errResult = errors.result

      if (errResult.isEmpty) IO.pure(Right(typedProg))
      else {
        // TODO: multiple traversal of error content, should be a foldleft or co
        given errorContent: String = contents
        val exitCode = errResult
          .collectFirst { case _: Error.InternalError =>
            201
          }
          .getOrElse(200)

        val formattedErrors = errResult.map(formatError).mkString("\n")

        logger.error(s"Semantic errors:\n$formattedErrors").as(Left(exitCode))
      }
  }
}

def backend(typedProg: microWacc.Program): Chain[asm.AsmLine] =
  asmGenerator.generateAsm(typedProg)

def compile(filePath: Path, outputDir: Option[Path], log: Boolean): IO[Int] = {
  val logAction: String => IO[Unit] =
    if (log) logger.info(_)
    else (_ => IO.unit)

  def readSourceFile: IO[String] =
    IO.blocking(os.read(os.Path(filePath)))

  def ensureOutputDir(outDir: Path): IO[Path] =
    IO.blocking {
      Files.createDirectories(outDir)
      outDir
    }.handleErrorWith {
      // TODO: I think this wont occur if a user runs with privileges but this must be checked
      // TODO: this will return the ugly stack trace, one could refactor compileCommand to
      case _: java.nio.file.AccessDeniedException =>
        IO.raiseError(
          new Exception(
            s"Permission denied: Cannot create directory '${outDir.toAbsolutePath}'. Try choosing a different output path or run as root."
          )
        )
    }

  // TODO: path, file , the names are confusing (when Path is the type but we are working with files)
  def writeOutputFile(typedProg: microWacc.Program, outputPath: Path): IO[Unit] =
    writer.writeTo(backend(typedProg), outputPath) *>
      logger.info(s"Success: ${outputPath.toAbsolutePath}")

  def processProgram(contents: String, outDir: Path): IO[Int] =
    frontend(contents).flatMap {
      case Left(code) =>
        logger.error(s"Compilation failed for $filePath\nExit code: $code").as(code)

      case Right(typedProg) =>
        val outputFile = outDir.resolve(filePath.getFileName.toString.stripSuffix(".wacc") + ".s")
        writeOutputFile(typedProg, outputFile).as(0)
    }

  for {
    contents <- readSourceFile
    _ <- logAction(s"Compiling file: ${filePath.toAbsolutePath}")
    outDir <- ensureOutputDir(outputDir.getOrElse(filePath.getParent))
    exitCode <- processProgram(contents, outDir)
  } yield exitCode
}

// TODO: Remove duplicate code between compileCommandSequential and compileCommandParallel
def compileCommandSequential(
    files: NonEmptyList[Path],
    log: Boolean,
    outDir: Option[Path]
): IO[ExitCode] =
  files
    .traverse { file =>
      compile(file.toAbsolutePath, outDir, log).handleErrorWith { err =>
        // TODO: probably a more elegant way of doing this
        // also, -1 arbitrary
        // also - this outputs two messages for some reason
        logger.error(err.getMessage) // *> IO.raiseError(err)
      }
    }
    .map { exitCodes =>
      if (exitCodes.exists(_ != 0)) ExitCode.Error else ExitCode.Success
    }

def compileCommandParallel(
    files: NonEmptyList[Path],
    log: Boolean,
    outDir: Option[Path]
): IO[ExitCode] =
  files
    .parTraverse { file =>
      compile(file.toAbsolutePath, outDir, log).handleErrorWith { err =>
        // TODO: probably a more elegant way of doing this
        // also, -1 arbitrary
        // also - this outputs two messages for some reason
        logger.error(err.getMessage) // *> IO.raiseError(err)
      }
    }
    .map { exitCodes =>
      if (exitCodes.exists(_ != 0)) ExitCode.Error else ExitCode.Success
    }

object Main
    extends CommandIOApp(
      name = "wacc",
      header = "The ultimate WACC compiler",
      version = "1.0"
    ) {
  def main: Opts[IO[ExitCode]] =
    (greedyOpt, filesOpt, logOpt, outputOpt).mapN { (greedy, files, log, outDir) =>
      if (greedy) compileCommandSequential(files, log, outDir)
      else compileCommandParallel(files, log, outDir)
    }

}