chart: fix multi-Y limit inconsistency (#1687)

When explicitly setting the axis it was inclusive of the
limit value meaning you could actually use one more than
the max setting. Settings like axis per line were honoring
the actual limit. Fixed them to be consistent and bumped
the configured limit by 1 for backwards compatibility with
any uses of the additional explicit axis.

atlas-chart/src/main/resources/reference.conf

@@ -86,7 +86,7 @@ atlas {
       max-height = 1000
       max-zoom = 2.0
       max-lines-in-legend = 50
-      max-yaxes = 4
+      max-yaxes = 5
     }
   }
 }

atlas-eval/src/main/scala/com/netflix/atlas/eval/graph/Grapher.scala

@@ -116,7 +116,7 @@ case class Grapher(settings: DefaultSettings) {
       .getOrElse(Features.STABLE)
 
     import com.netflix.atlas.chart.GraphConstants.*
-    val axes = (0 to MaxYAxis).map(i => i -> newAxis(params, i)).toMap
+    val axes = (0 until MaxYAxis).map(i => i -> newAxis(params, i)).toMap
 
     val vision = params.get("vision").map(v => VisionType.valueOf(v))
 
@@ -311,7 +311,7 @@ case class Grapher(settings: DefaultSettings) {
 
     val plots = plotExprs.toList.sortWith(_._1 < _._1).map {
       case (yaxis, exprs) =>
-        val axisCfg = config.flags.axes(yaxis)
+        val axisCfg = config.flags.getAxis(yaxis)
         val dfltStyle = if (axisCfg.stack) LineStyle.STACK else LineStyle.LINE
 
         val statFormatter = axisCfg.tickLabelMode match {

atlas-eval/src/main/scala/com/netflix/atlas/eval/graph/ImageFlags.scala

@@ -45,4 +45,11 @@ case class ImageFlags(
       case None       => settings.primaryPalette(theme)
     }
   }
+
+  def getAxis(index: Int): Axis = {
+    axes.get(index) match {
+      case Some(axis) => axis
+      case None       => throw new IllegalArgumentException(s"invalid axis: $index")
+    }
+  }
 }

atlas-eval/src/test/scala/com/netflix/atlas/eval/graph/GrapherSuite.scala

@@ -290,6 +290,25 @@ class GrapherSuite extends FunSuite {
       "&ylabel.0=Axis%200&ylabel.1=Axis%201"
   }
 
+  imageTest("multi-Y, 5 axes") {
+    "/api/v1/graph?e=2012-01-01T00:00&q=(,0,1,2,3,4,),(,:dup,:axis,),:each"
+  }
+
+  test("multi-Y, 6 axes") {
+    val uri = "/api/v1/graph?e=2012-01-01T00:00&q=(,0,1,2,3,4,6,),(,:dup,:axis,),:each"
+    intercept[IllegalArgumentException] {
+      grapher.evalAndRender(Uri(uri), db)
+    }
+  }
+
+  imageTest("multi-Y, 5 axis per line") {
+    "/api/v1/graph?e=2012-01-01T00:00&q=0,1,2,3,4&axis_per_line=1"
+  }
+
+  imageTest("multi-Y, 6 axis per line") {
+    "/api/v1/graph?e=2012-01-01T00:00&q=0,1,2,3,4,6&axis_per_line=1"
+  }
+
   imageTest("significant time boundaries and tz=US/Pacific") {
     "/api/v1/graph?q=name,sps,:eq,:sum&s=e-2d&e=2015-06-17T13:13&no_legend=1&tz=US/Pacific"
   }