CMM-2001: Replace previous-period line with stacked bars in Views chart (#22752)

* Replace previous-period line with stacked bars in Views chart

Use stacked column bars instead of a dashed line overlay to show
previous period data in the bar chart mode of the Views stats card.
When the previous period exceeds the current, a grey bar stacks on
top to reach the previous value.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Round bar tops only when no stacked bar is present

Use three stacked series so that bars without a grey delta
portion get rounded tops while bars with a stacked grey
portion stay flat, with only the grey bar rounded on top.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Reduce bar chart corner rounding from 40% to 20%

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: adalpari

WordPress/src/main/java/org/wordpress/android/ui/newstats/viewsstats/ViewsStatsCard.kt

@@ -79,6 +79,7 @@ import com.patrykandpatrick.vico.core.cartesian.marker.CartesianMarkerVisibility
 import com.patrykandpatrick.vico.core.cartesian.marker.DefaultCartesianMarker
 import com.patrykandpatrick.vico.compose.cartesian.layer.rememberColumnCartesianLayer
 import com.patrykandpatrick.vico.compose.cartesian.layer.rememberLineCartesianLayer
+import com.patrykandpatrick.vico.compose.cartesian.layer.stacked
 import com.patrykandpatrick.vico.compose.cartesian.rememberCartesianChart
 import com.patrykandpatrick.vico.compose.cartesian.rememberVicoScrollState
 import com.patrykandpatrick.vico.core.common.Insets
@@ -520,13 +521,45 @@ private fun ViewsStatsChart(
                 }
                 ChartType.BAR -> modelProducer.runTransaction {
                     columnSeries {
-                        series(chartData.currentPeriod.map { it.views.toInt() })
-                    }
-                    if (hasPreviousPeriod) {
-                        lineSeries {
+                        if (hasPreviousPeriod) {
+                            // Series 1: current value when no
+                            // delta (rounded top)
+                            series(
+                                chartData.currentPeriod.zip(
+                                    chartData.previousPeriod
+                                ) { current, previous ->
+                                    if (previous.views <= current.views)
+                                        current.views.toInt()
+                                    else 0
+                                }
+                            )
+                            // Series 2: current value when there
+                            // is a delta (flat top)
+                            series(
+                                chartData.currentPeriod.zip(
+                                    chartData.previousPeriod
+                                ) { current, previous ->
+                                    if (previous.views > current.views)
+                                        current.views.toInt()
+                                    else 0
+                                }
+                            )
+                            // Series 3: delta (rounded top)
+                            series(
+                                chartData.currentPeriod.zip(
+                                    chartData.previousPeriod
+                                ) { current, previous ->
+                                    maxOf(
+                                        0L,
+                                        previous.views - current.views
+                                    ).toInt()
+                                }
+                            )
+                        } else {
                             series(
-                                chartData.previousPeriod
-                                    .map { it.views.toInt() }
+                                chartData.currentPeriod.map {
+                                    it.views.toInt()
+                                }
                             )
                         }
                     }
@@ -677,26 +710,26 @@ private fun ViewsStatsChart(
                                     fill = fill(primaryColor),
                                     thicknessDp = 16f,
                                     shape = CorneredShape.rounded(
-                                        allPercent = 40
+                                        topLeftPercent = 20,
+                                        topRightPercent = 20,
+                                    )
+                                ),
+                                LineComponent(
+                                    fill = fill(primaryColor),
+                                    thicknessDp = 16f,
+                                ),
+                                LineComponent(
+                                    fill = fill(secondaryColor),
+                                    thicknessDp = 16f,
+                                    shape = CorneredShape.rounded(
+                                        topLeftPercent = 20,
+                                        topRightPercent = 20,
                                     )
                                 )
-                            )
-                    ),
-                    rememberLineCartesianLayer(
-                        lineProvider = LineCartesianLayer
-                            .LineProvider.series(
-                                LineCartesianLayer.Line(
-                                    fill = LineCartesianLayer
-                                        .LineFill.single(
-                                            fill(secondaryColor)
-                                        ),
-                                    stroke = LineCartesianLayer
-                                        .LineStroke.Dashed(),
-                                    pointConnector =
-                                        LineCartesianLayer
-                                            .PointConnector.Sharp
-                                )
-                            )
+                            ),
+                        mergeMode = {
+                            ColumnCartesianLayer.MergeMode.stacked()
+                        }
                     ),
                     startAxis = VerticalAxis.rememberStart(
                         line = null