/*
 * Scala (https://www.scala-lang.org)
 *
 * Copyright EPFL and Lightbend, Inc.
 *
 * Licensed under Apache License 2.0
 * (http://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

package scala
package reflect.internal.util

import scala.reflect.io.{AbstractFile, VirtualFile}
import scala.collection.mutable.ArrayBuilder
import scala.annotation.tailrec
import java.util.regex.Pattern
import java.io.IOException
import scala.reflect.internal.Chars._
import PartialFunction.cond

/** abstract base class of a source file used in the compiler */
abstract class SourceFile {
  def content: Array[Char]         // normalized, must end in SU
  def file   : AbstractFile
  def isLineBreak(idx: Int): Boolean
  def isEndOfLine(idx: Int): Boolean
  def isSelfContained: Boolean
  def length : Int
  def lineCount: Int
  def position(offset: Int): Position = {
    assert(offset < length, file.toString + ": " + offset + " >= " + length)
    Position.offset(this, offset)
  }

  def offsetToLine(offset: Int): Int
  def lineToOffset(index : Int): Int

  /** Map a position to a position in the underlying source file.
   *  For regular source files, simply return the argument.
   */
  def positionInUltimateSource(position: Position) = position
  override def toString() = file.name
  def path = file.path

  def lineToString(index: Int): String = {
    val start = lineToOffset(index)
    var end = start
    while (end < length && !isEndOfLine(end)) end += 1
    new String(content, start, end - start)
  }

  @tailrec
  final def skipWhitespace(offset: Int): Int =
    if (content(offset).isWhitespace) skipWhitespace(offset + 1) else offset

  def identFrom(pos: Position): Option[String] =
    Option.when(pos.isDefined && pos.source == this && pos.point != -1) {
      def isOK(c: Char) = isIdentifierPart(c) || isOperatorPart(c)
      new String(content drop pos.point takeWhile isOK)
    }

  def sourceAt(pos: Position): String =
    if (pos.start < pos.end) new String(content.slice(pos.start, pos.end)) else ""

  def indexWhere(p: Char => Boolean, start: Int, step: Int = 1): Int = {
    var i = start
    while (i >= 0 && i < content.length) {
      if (p(content(i))) return i
      i += step
    }
    -1
  }

  /** An iterator over the lines between `start` and `end`.
    *
    * Bounds are checked and clipped as necessary.
    */
  def lines(start: Int = 0, end: Int = lineCount): Iterator[String]

  final def isJava: Boolean = file.name endsWith ".java"
}

/** An object representing a missing source file.
 */
object NoSourceFile extends SourceFile {
  def content                     = Array()
  def file                        = NoFile
  def isLineBreak(idx: Int)       = false
  def isEndOfLine(idx: Int)       = false
  def isSelfContained             = true
  def length                      = -1
  def lineCount                   = 0
  def offsetToLine(offset: Int)   = -1
  def lineToOffset(index : Int)   = -1
  def lines(start: Int, end: Int) = Iterator.empty
  override def toString           = "<no source file>"
}

object NoFile extends VirtualFile("<no file>", "<no file>")

object ScriptSourceFile {
  /** Length of the script header from the given content, if there is one.
   *  The header begins with "#!" or "::#!" and ends with a line starting
   *  with "!#" or "::!#".
   */
  def headerLength(cs: Array[Char]): Int = {
    val headerPattern = Pattern.compile("""((?m)^(::)?!#.*|^.*/env .*)(\r|\n|\r\n)""")
    val headerStarts  = List("#!", "::#!")

    if (headerStarts exists (cs startsWith _)) {
      val matcher = headerPattern matcher cs.mkString
      if (matcher.find) matcher.end
      else throw new IOException("script file does not close its header with !# or ::!#")
    }
    else 0
  }

  def apply(file: AbstractFile, content: Array[Char]) = {
    val underlying = new BatchSourceFile(file, content)
    val headerLen = headerLength(content)
    val stripped = new ScriptSourceFile(underlying, content drop headerLen, headerLen)

    stripped
  }

  def apply(underlying: BatchSourceFile) = {
    val headerLen = headerLength(underlying.content)
    new ScriptSourceFile(underlying, underlying.content drop headerLen, headerLen)
  }
}

class ScriptSourceFile(underlying: BatchSourceFile, content: Array[Char], override val start: Int) extends BatchSourceFile(underlying.file, content) {
  override def isSelfContained = false

  override def positionInUltimateSource(pos: Position) =
    if (!pos.isDefined) super.positionInUltimateSource(pos)
    else pos withSource underlying withShift start
}

/* See PerRunReporting.repSrc */
class ReplBatchSourceFile(filename: String, content: String, val parserSource: BatchSourceFile)
  extends BatchSourceFile(filename, content)

/** a file whose contents do not change over time */
class BatchSourceFile(val file : AbstractFile, content0: Array[Char]) extends SourceFile {
  def this(_file: AbstractFile)                 = this(_file, _file.toCharArray)
  def this(sourceName: String, cs: Seq[Char])   = this(new VirtualFile(sourceName), cs.toArray)
  def this(file: AbstractFile, cs: Seq[Char])   = this(file, cs.toArray)

  // If non-whitespace tokens run all the way up to EOF,
  // positions go wrong because the correct end of the last
  // token cannot be used as an index into the char array.
  // The least painful way to address this was to add a
  // newline to the array.
  val content = (
    if (content0.length == 0 || !content0.last.isWhitespace)
      content0 :+ '\n'
    else content0
  )
  def length = content.length
  def lineCount = lineIndices.length - 1
  def start = 0
  def isSelfContained = true

  private def charAtIsEOL(idx: Int)(p: Char => Boolean) = {
    // don't identify the CR in CR LF as a line break, since LF will do.
    def notCRLF0 = content(idx) != CR || !content.isDefinedAt(idx + 1) || content(idx + 1) != LF

    idx < length && notCRLF0 && p(content(idx))
  }

  def isLineBreak(idx: Int) = charAtIsEOL(idx)(isLineBreakChar)

  /** True if the index is included by an EOL sequence. */
  def isEndOfLine(idx: Int) = content.isDefinedAt(idx) && cond(content(idx)) { case CR | LF => true }

  /** True if the index is end of an EOL sequence. */
  def isAtEndOfLine(idx: Int) = charAtIsEOL(idx)(c => c == CR || c == LF)

  private lazy val lineIndices: Array[Int] = {
    def calculateLineIndices(cs: Array[Char]) = {
      val buf = new ArrayBuilder.ofInt
      buf.sizeHint(cs.length / 30)       // pick a short avg line length and hope to avoid reallocation and extra copy
      buf.addOne(0)
      @tailrec def fillLines(i: Int): Unit =
        if (i < cs.length) {
          if (isAtEndOfLine(i)) buf.addOne(i + 1)
          fillLines(i + 1)
        }
      fillLines(0)
      buf.addOne(cs.length)              // sentinel, so that findLine below works smoother
      buf.result()
    }
    calculateLineIndices(content)
  }

  def lineToOffset(index: Int): Int =
    lineIndices(index) match {
      case offset if offset < length => offset
      case _ => throw new IndexOutOfBoundsException(index.toString)
    }

  private[this] var lastLine = 0

  /** Convert offset to line in this source file.
   *  Lines are numbered from 0.
   */
  def offsetToLine(offset: Int): Int = {
    val lines = lineIndices
    if (lines.isEmpty || offset < lines.head || offset >= lines.last) throw new IndexOutOfBoundsException(offset.toString)
    @tailrec
    def findLine(lo: Int, hi: Int, mid: Int): Int = (
      if (mid < lo || hi < mid) mid // minimal confidence check - as written this easily went into infinite loopyland
      else if (offset < lines(mid)) findLine(lo, mid - 1, (lo + mid - 1) / 2)
      else if (offset >= lines(mid + 1)) findLine(mid + 1, hi, (mid + 1 + hi) / 2)
      else mid
    )
    lastLine = findLine(0, lines.length, lastLine)
    lastLine
  }

  override def lines(start: Int, end: Int): Iterator[String] =
    ((start max 0) until (end min lineCount)).iterator.map { ix =>
      val off = lineIndices(ix)
      val len = 0 max (lineIndices(ix + 1) - off - 1) // drop newline character
      String.valueOf(content, off, len)
    }


  override def equals(that : Any) = that match {
    case that: BatchSourceFile if !file.isVirtual && !that.file.isVirtual => file.path == that.file.path && start == that.start
    case _ => super.equals(that)
  }
  override def hashCode = if (!file.isVirtual) file.path.## + start.## else super.hashCode()
}
