Merge pull request #351 from guymers/query-parsing-pref

Improve query parsing performance

src/main/scala/sangria/parser/PositionTracking.scala

@@ -3,18 +3,55 @@ package sangria.parser
 import org.parboiled2._
 import sangria.ast.AstLocation
 
+import scala.annotation.tailrec
+
 trait PositionTracking { this: Parser ⇒
-  private var lineIdx = Vector(0)
+  private var lineIdx = Array(0)
 
   def sourceId: String
 
-  def trackNewLine: Rule0 = rule { run(if (!(lineIdx contains cursor)) lineIdx = lineIdx :+ cursor) }
+  def trackNewLine: Rule0 = rule {
+    run {
+      if (!contains(lineIdx, cursor)) lineIdx = lineIdx :+ cursor
+    }
+  }
 
   def trackPos = rule {
     push {
-      val currLines = lineIdx.takeWhile(_ <= cursor)
+      val (size, lastCursor) = findLastItem(lineIdx, cursor)
+
+      AstLocation(sourceId, cursor, size, cursor - lastCursor + 1)
+    }
+  }
 
-      AstLocation(sourceId, cursor, currLines.size, cursor - currLines.last + 1)
+  /**
+    * Returns true if the array contains the given item.
+    *
+    * Assumes that the array is sorted in ascending order.
+    */
+  private def contains(arr: Array[Int], item: Int) = {
+    @tailrec def go(i: Int): Boolean = {
+      if (i < 0) false
+      else if (arr(i) < item) false // no remaining values will match as the array is sorted
+      else if (arr(i) == item) true
+      else go(i - 1)
     }
+    go(arr.length - 1)
   }
+
+  /**
+    * Returns the first item that is less than or equal to the given item
+    * along with the number of elements that come before it.
+    *
+    * Assumes that the array is sorted in ascending order.
+    */
+  private def findLastItem(arr: Array[Int], item: Int) = {
+    @tailrec def go(i: Int, last: Int): (Int, Int) = {
+      if (i < 0) (i + 1, last)
+      else if (arr(i) <= item) (i + 1, arr(i))
+      else go(i - 1, arr(i))
+    }
+    go(arr.length - 1, 0)
+  }
+
 }