feat: Add Grouped Charts support (#17)

library/src/main/java/com/dzeio/charts/ChartType.kt

@@ -0,0 +1,21 @@
+package com.dzeio.charts
+
+enum class ChartType {
+
+    /**
+     * Basic Chart where items go over the other
+     */
+    BASIC,
+
+    /**
+     * each series are next to each other nicely
+     */
+    GROUPED,
+
+    /**
+     * WILL NOT DO ANYTHING CURRENTLY
+     *
+     * Each series are stacked over the other one
+     */
+    STACKED
+}

library/src/main/java/com/dzeio/charts/ChartView.kt

@@ -21,6 +21,8 @@ class ChartView @JvmOverloads constructor(context: Context?, attrs: AttributeSet
         const val TAG = "Charts/ChartView"
     }
 
+    override var type: ChartType = ChartType.BASIC
+
     override var debug: Boolean = false
 
     override val xAxis = XAxis(this)

library/src/main/java/com/dzeio/charts/ChartViewInterface.kt

@@ -6,6 +6,11 @@ import com.dzeio.charts.series.SerieInterface
 
 interface ChartViewInterface {
 
+    /**
+     * Chart Type
+     */
+    var type: ChartType
+
     /**
      * Make the whole view in debug mode
      *

library/src/main/java/com/dzeio/charts/axis/XAxis.kt

@@ -5,6 +5,7 @@ import android.graphics.Color
 import android.graphics.Paint
 import android.graphics.Rect
 import android.graphics.RectF
+import com.dzeio.charts.ChartType
 import com.dzeio.charts.ChartViewInterface
 import com.dzeio.charts.Entry
 import kotlin.math.roundToInt
@@ -51,11 +52,13 @@ class XAxis(
     }
 
     override fun getPositionOnRect(entry: Entry, drawableSpace: RectF): Double {
-        return translatePositionToRect(entry.x, drawableSpace)
-    }
-
-    fun translatePositionToRect(value: Double, drawableSpace: RectF): Double {
-        return drawableSpace.width() * (value - x) / getDataWidth()
+        val result = drawableSpace.width() * (entry.x - x) / getDataWidth()
+        if (view.type == ChartType.GROUPED) {
+            val serie = view.series.find { it.entries.contains(entry) }
+            val index = view.series.indexOf(serie)
+            return result + getEntryWidth(drawableSpace) * index + spacing / 2 * index
+        }
+        return result
     }
 
     override fun getXMax(): Double {
@@ -123,8 +126,15 @@ class XAxis(
             }
         }
 
-        return (drawableSpace.width() * smallest / getDataWidth() - spacing)
+        val result = (drawableSpace.width() * smallest / getDataWidth() - spacing)
             .coerceIn(1.0, drawableSpace.width().toDouble())
+
+        // handle grouped series
+        if (view.type == ChartType.GROUPED) {
+            return result / view.series.size - spacing / 2 * (view.series.size - 1)
+        }
+
+        return result
     }
 
     override fun getDataWidth(): Double {