package coursier

import java.net.{HttpURLConnection, URL}
import java.nio.channels.{ OverlappingFileLockException, FileLock }
import java.nio.file.{ StandardCopyOption, Files => NioFiles }
import java.security.MessageDigest
import java.util.concurrent.{ConcurrentHashMap, Executors, ExecutorService}

import coursier.ivy.IvyRepository

import scala.annotation.tailrec
import scalaz._
import scalaz.concurrent.{ Task, Strategy }

import java.io.{ Serializable => _, _ }

object Cache {

  // Check SHA-1 if available, else be fine with no checksum
  val defaultChecksums = Seq(Some("SHA-1"), None)

  private def withLocal(artifact: Artifact, cache: Seq[(String, File)]): Artifact = {
    def local(url: String) =
      if (url.startsWith("file:///"))
        url.stripPrefix("file://")
      else if (url.startsWith("file:/"))
        url.stripPrefix("file:")
      else {
        val localPathOpt = cache.collectFirst {
          case (base, cacheDir) if url.startsWith(base) =>
            cacheDir + "/" + url.stripPrefix(base)
        }

        localPathOpt.getOrElse {
          // FIXME Means we were handed an artifact from repositories other than the known ones
          println(cache.mkString("\n"))
          println(url)
          ???
        }
      }

    if (artifact.extra.contains("local"))
      artifact
    else
      artifact.copy(extra = artifact.extra + ("local" ->
        artifact.copy(
          url = local(artifact.url),
          checksumUrls = artifact.checksumUrls
            .mapValues(local)
            .toVector
            .toMap,
          extra = Map.empty
        )
      ))
  }

  private def readFullyTo(
    in: InputStream,
    out: OutputStream,
    logger: Option[Logger],
    url: String,
    alreadyDownloaded: Long
  ): Unit = {

    val b = Array.fill[Byte](bufferSize)(0)

    @tailrec
    def helper(count: Long): Unit = {
      val read = in.read(b)
      if (read >= 0) {
        out.write(b, 0, read)
        out.flush()
        logger.foreach(_.downloadProgress(url, count + read))
        helper(count + read)
      }
    }

    helper(alreadyDownloaded)
  }

  private def withLockFor[T](file: File)(f: => FileError \/ T): FileError \/ T = {
    val lockFile = new File(file.getParentFile, s"${file.getName}.lock")

    lockFile.getParentFile.mkdirs()
    var out = new FileOutputStream(lockFile)

    try {
      var lock: FileLock = null
      try {
        lock = out.getChannel.tryLock()
        if (lock == null)
          -\/(FileError.Locked(file))
        else
          try f
          finally {
            lock.release()
            lock = null
            out.close()
            out = null
            lockFile.delete()
          }
      }
      catch {
        case e: OverlappingFileLockException =>
          -\/(FileError.Locked(file))
      }
      finally if (lock != null) lock.release()
    } finally if (out != null) out.close()
  }

  private def downloading[T](
    url: String,
    file: File,
    logger: Option[Logger]
  )(
    f: => FileError \/ T
  ): FileError \/ T =
    try {
      val o = new Object
      val prev = urlLocks.putIfAbsent(url, o)
      if (prev == null) {
        logger.foreach(_.downloadingArtifact(url, file))

        val res =
          try \/-(f)
          catch {
            case nfe: FileNotFoundException if nfe.getMessage != null =>
              logger.foreach(_.downloadedArtifact(url, success = false))
              -\/(-\/(FileError.NotFound(nfe.getMessage)))
            case e: Exception =>
              logger.foreach(_.downloadedArtifact(url, success = false))
              throw e
          }
          finally {
            urlLocks.remove(url)
          }

        for (res0 <- res)
          logger.foreach(_.downloadedArtifact(url, success = res0.isRight))

        res.merge
      } else
        -\/(FileError.ConcurrentDownload(url))
    }
    catch { case e: Exception =>
      -\/(FileError.DownloadError(s"Caught $e (${e.getMessage})"))
    }

  private def temporaryFile(file: File): File = {
    val dir = file.getParentFile
    val name = file.getName
    new File(dir, s"$name.part")
  }

  private val partialContentResponseCode = 206

  private def download(
    artifact: Artifact,
    cache: Seq[(String, File)],
    checksums: Set[String],
    cachePolicy: CachePolicy,
    pool: ExecutorService,
    logger: Option[Logger] = None
  ): Task[Seq[((File, String), FileError \/ Unit)]] = {

    implicit val pool0 = pool

    val artifact0 = withLocal(artifact, cache)
      .extra
      .getOrElse("local", artifact)

    val pairs =
      Seq(artifact0.url -> artifact.url) ++ {
        checksums
          .intersect(artifact0.checksumUrls.keySet)
          .intersect(artifact.checksumUrls.keySet)
          .toSeq
          .map(sumType => artifact0.checksumUrls(sumType) -> artifact.checksumUrls(sumType))
      }

    def urlConn(url: String) = {
      val conn = new URL(url).openConnection() // FIXME Should this be closed?
      // Dummy user-agent instead of the default "Java/...",
      // so that we are not returned incomplete/erroneous metadata
      // (Maven 2 compatibility? - happens for snapshot versioning metadata,
      // this is SO FSCKING CRAZY)
      conn.setRequestProperty("User-Agent", "")
      conn
    }


    def fileLastModified(file: File): EitherT[Task, FileError, Option[Long]] =
      EitherT {
        Task {
          \/- {
            val lastModified = file.lastModified()
            if (lastModified > 0L)
              Some(lastModified)
            else
              None
          } : FileError \/ Option[Long]
        }
      }

    def urlLastModified(url: String): EitherT[Task, FileError, Option[Long]] =
      EitherT {
        Task {
          urlConn(url) match {
            case c: HttpURLConnection =>
              c.setRequestMethod("HEAD")
              val remoteLastModified = c.getLastModified

              \/- {
                if (remoteLastModified > 0L)
                  Some(remoteLastModified)
                else
                  None
              }

            case other =>
              -\/(FileError.DownloadError(s"Cannot do HEAD request with connection $other ($url)"))
          }
        }
      }

    def shouldDownload(file: File, url: String): EitherT[Task, FileError, Boolean] =
      for {
        fileLastModOpt <- fileLastModified(file)
        urlLastModOpt <- urlLastModified(url)
      } yield {
        val fromDatesOpt = for {
          fileLastMod <- fileLastModOpt
          urlLastMod <- urlLastModOpt
        } yield fileLastMod < urlLastMod

        fromDatesOpt.getOrElse(true)
      }

    def remote(file: File, url: String): EitherT[Task, FileError, Unit] =
      EitherT {
        Task {
          withLockFor(file) {
            downloading(url, file, logger) {
              val tmp = temporaryFile(file)

              val alreadyDownloaded = tmp.length()

              val conn0 = urlConn(url)

              val (partialDownload, conn) = conn0 match {
                case conn0: HttpURLConnection if alreadyDownloaded > 0L =>
                  conn0.setRequestProperty("Range", s"bytes=$alreadyDownloaded-")

                  if (conn0.getResponseCode == partialContentResponseCode) {
                    val ackRange = Option(conn0.getHeaderField("Content-Range")).getOrElse("")

                    if (ackRange.startsWith(s"bytes $alreadyDownloaded-"))
                      (true, conn0)
                    else
                      // unrecognized Content-Range header -> start a new connection with no resume
                      (false, urlConn(url))
                  } else
                    (false, conn0)

                case _ => (false, conn0)
              }

              for (len0 <- Option(conn.getContentLengthLong) if len0 >= 0L) {
                val len = len0 + (if (partialDownload) alreadyDownloaded else 0L)
                logger.foreach(_.downloadLength(url, len))
              }

              val in = new BufferedInputStream(conn.getInputStream, bufferSize)

              val result =
                try {
                  tmp.getParentFile.mkdirs()
                  val out = new FileOutputStream(tmp, partialDownload)
                  try \/-(readFullyTo(in, out, logger, url, if (partialDownload) alreadyDownloaded else 0L))
                  finally out.close()
                } finally in.close()

              file.getParentFile.mkdirs()
              NioFiles.move(tmp.toPath, file.toPath, StandardCopyOption.ATOMIC_MOVE)

              for (lastModified <- Option(conn.getLastModified) if lastModified > 0L)
                file.setLastModified(lastModified)

              result
            }
          }
        }
      }

    def checkFileExists(file: File, url: String): EitherT[Task, FileError, Unit] =
      EitherT {
        Task {
          if (file.exists()) {
            logger.foreach(_.foundLocally(url, file))
            \/-(())
          } else
            -\/(FileError.NotFound(file.toString))
        }
      }

    val tasks =
      for ((f, url) <- pairs) yield {
        val file = new File(f)

        val res =
          if (url.startsWith("file:/")) {
            // for debug purposes, flaky with URL-encoded chars anyway
            // def filtered(s: String) =
            //   s.stripPrefix("file:/").stripPrefix("//").stripSuffix("/")
            // assert(
            //   filtered(url) == filtered(file.toURI.toString),
            //   s"URL: ${filtered(url)}, file: ${filtered(file.toURI.toString)}"
            // )
            checkFileExists(file, url)
          } else
            cachePolicy match {
              case CachePolicy.LocalOnly =>
                checkFileExists(file, url)
              case CachePolicy.UpdateChanging | CachePolicy.Update =>
                shouldDownload(file, url).flatMap {
                  case true =>
                    remote(file, url)
                  case false =>
                    EitherT(Task.now(\/-(()) : FileError \/ Unit))
                }
              case CachePolicy.FetchMissing =>
                checkFileExists(file, url) orElse remote(file, url)
              case CachePolicy.ForceDownload =>
                remote(file, url)
            }

        res.run.map((file, url) -> _)
      }

    Nondeterminism[Task].gather(tasks)
  }

  def validateChecksum(
    artifact: Artifact,
    sumType: String,
    cache: Seq[(String, File)],
    pool: ExecutorService
  ): EitherT[Task, FileError, Unit] = {

    implicit val pool0 = pool

    val artifact0 = withLocal(artifact, cache)
      .extra
      .getOrElse("local", artifact)

    EitherT {
      artifact0.checksumUrls.get(sumType) match {
        case Some(sumFile) =>
          Task {
            val sum = new String(NioFiles.readAllBytes(new File(sumFile).toPath), "UTF-8")
              .linesIterator
              .toStream
              .headOption
              .mkString
              .takeWhile(!_.isSpaceChar)

            val f = new File(artifact0.url)
            val md = MessageDigest.getInstance(sumType)
            val is = new FileInputStream(f)
            val res = try {
              var lock: FileLock = null
              try {
                lock = is.getChannel.tryLock(0L, Long.MaxValue, true)
                if (lock == null)
                  -\/(FileError.Locked(f))
                else {
                  withContent(is, md.update(_, 0, _))
                  \/-(())
                }
              }
              catch {
                case e: OverlappingFileLockException =>
                  -\/(FileError.Locked(f))
              }
              finally if (lock != null) lock.release()
            } finally is.close()

            res.flatMap { _ =>
              val digest = md.digest()
              val calculatedSum = f"${BigInt(1, digest)}%040x"

              if (sum == calculatedSum)
                \/-(())
              else
                -\/(FileError.WrongChecksum(sumType, calculatedSum, sum, artifact0.url, sumFile))
            }
          }

        case None =>
          Task.now(-\/(FileError.ChecksumNotFound(sumType, artifact0.url)))
      }
    }
  }

  def file(
    artifact: Artifact,
    cache: Seq[(String, File)] = default,
    cachePolicy: CachePolicy = CachePolicy.FetchMissing,
    checksums: Seq[Option[String]] = defaultChecksums,
    logger: Option[Logger] = None,
    pool: ExecutorService = defaultPool
  ): EitherT[Task, FileError, File] = {

    implicit val pool0 = pool

    val checksums0 = if (checksums.isEmpty) Seq(None) else checksums

    val res = EitherT {
      download(
        artifact,
        cache,
        checksums = checksums0.collect { case Some(c) => c }.toSet,
        cachePolicy,
        pool,
        logger = logger
      ).map { results =>
        val checksum = checksums0.find {
          case None => true
          case Some(c) =>
            artifact.checksumUrls.get(c).exists { cUrl =>
              results.exists { case ((_, u), b) =>
                u == cUrl && b.isRight
              }
            }
        }

        val ((f, _), res) = results.head
        res.flatMap { _ =>
          checksum match {
            case None =>
              // FIXME All the checksums should be in the error, possibly with their URLs
              //       from artifact.checksumUrls
              -\/(FileError.ChecksumNotFound(checksums0.last.get, ""))
            case Some(c) => \/-((f, c))
          }
        }
      }
    }

    res.flatMap {
      case (f, None) => EitherT(Task.now[FileError \/ File](\/-(f)))
      case (f, Some(c)) =>
        validateChecksum(artifact, c, cache, pool).map(_ => f)
    }
  }

  def fetch(
    cache: Seq[(String, File)] = default,
    cachePolicy: CachePolicy = CachePolicy.FetchMissing,
    checksums: Seq[Option[String]] = defaultChecksums,
    logger: Option[Logger] = None,
    pool: ExecutorService = defaultPool
  ): Fetch.Content[Task] = {
    artifact =>
      file(
        artifact,
        cache,
        cachePolicy,
        checksums = checksums,
        logger = logger,
        pool = pool
      ).leftMap(_.message).map { f =>
        // FIXME Catch error here?
        new String(NioFiles.readAllBytes(f.toPath), "UTF-8")
      }
  }

  private lazy val ivy2HomeUri = {
    // a bit touchy on Windows... - don't try to manually write down the URI with s"file://..."
    val str = new File(sys.props("user.home") + "/.ivy2/").toURI.toString
    if (str.endsWith("/"))
      str
    else
      str + "/"
  }

  lazy val ivy2Local = IvyRepository(
    ivy2HomeUri + "local/" +
      "[organisation]/[module]/(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[revision]/[type]s/" +
      "[artifact](-[classifier]).[ext]",
    dropInfoAttributes = true
  )

  lazy val ivy2Cache = IvyRepository(
    ivy2HomeUri + "cache/" +
      "(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[organisation]/[module]/[type]s/[artifact]-[revision](-[classifier]).[ext]",
    metadataPatternOpt = Some(
      ivy2HomeUri + "cache/" +
        "(scala_[scalaVersion]/)(sbt_[sbtVersion]/)[organisation]/[module]/[type]-[revision](-[classifier]).[ext]"
    ),
    withChecksums = false,
    withSignatures = false,
    dropInfoAttributes = true
  )

  lazy val defaultBase = new File(
    sys.env.getOrElse(
      "COURSIER_CACHE",
      sys.props("user.home") + "/.coursier/cache/v1"
    )
  ).getAbsoluteFile

  lazy val default = Seq(
    "http://" -> new File(defaultBase, "http"),
    "https://" -> new File(defaultBase, "https")
  )

  val defaultConcurrentDownloadCount = 6

  lazy val defaultPool =
    Executors.newFixedThreadPool(defaultConcurrentDownloadCount, Strategy.DefaultDaemonThreadFactory)


  private val urlLocks = new ConcurrentHashMap[String, Object]

  trait Logger {
    def foundLocally(url: String, f: File): Unit = {}
    def downloadingArtifact(url: String, file: File): Unit = {}
    def downloadLength(url: String, length: Long): Unit = {}
    def downloadProgress(url: String, downloaded: Long): Unit = {}
    def downloadedArtifact(url: String, success: Boolean): Unit = {}
  }

  var bufferSize = 1024*1024

  def readFullySync(is: InputStream) = {
    val buffer = new ByteArrayOutputStream()
    val data = Array.ofDim[Byte](16384)

    var nRead = is.read(data, 0, data.length)
    while (nRead != -1) {
      buffer.write(data, 0, nRead)
      nRead = is.read(data, 0, data.length)
    }

    buffer.flush()
    buffer.toByteArray
  }

  def readFully(is: => InputStream) =
    Task {
      \/.fromTryCatchNonFatal {
        val is0 = is
        val b =
          try readFullySync(is0)
          finally is0.close()

        new String(b, "UTF-8")
      } .leftMap(_.getMessage)
    }

  def withContent(is: InputStream, f: (Array[Byte], Int) => Unit): Unit = {
    val data = Array.ofDim[Byte](16384)

    var nRead = is.read(data, 0, data.length)
    while (nRead != -1) {
      f(data, nRead)
      nRead = is.read(data, 0, data.length)
    }
  }

}

sealed abstract class FileError(val message: String) extends Product with Serializable

object FileError {

  final case class DownloadError(reason: String) extends FileError(s"Download error: $reason")

  final case class NotFound(file: String) extends FileError(s"Not found: $file")

  final case class ChecksumNotFound(
    sumType: String,
    file: String
  ) extends FileError(s"$sumType checksum not found: $file")

  final case class WrongChecksum(
    sumType: String,
    got: String,
    expected: String,
    file: String,
    sumFile: String
  ) extends FileError(s"$sumType checksum validation failed: $file")

  sealed abstract class Recoverable(message: String) extends FileError(message)
  final case class Locked(file: File) extends Recoverable(s"Locked: $file")
  final case class ConcurrentDownload(url: String) extends Recoverable(s"Concurrent download: $url")

}