add vertical option for custom-grid, add dev docs

component/charts/custom-grid.tsx

@@ -1,14 +1,45 @@
 import React from 'react';
 import { G, Line } from 'react-native-svg';
 import { colors } from '../../styles';
-import { ScaleLinearType } from './graph-types';
+import { ScaleBandType, ScaleLinearType } from './graph-types';
 
 interface CustomGridProps {
+  x: ScaleBandType;
   y: ScaleLinearType;
   ticks: Array<number>;
+  includeVertical?: boolean;
+  xTicks?: Array<number | string>;
 }
-
-export const CustomGrid: React.FC<Partial<CustomGridProps>> = ({ y, ticks }) => {
+/**
+ * CustomGrid Component
+ * 
+ * This component is used within a react-native-svg-chart component to render grid lines.
+ * 
+ * @param {ScaleBandType} x - X-axis scale function, received from the parent chart component.
+ * @param {ScaleLinearType} y - Y-axis scale function, received from the parent chart component.
+ * @param {Array<number>} ticks - Y-axis tick values for horizontal lines, received from the parent.
+ * @param {boolean} [includeVertical=false] - Enables experimental vertical grid lines.
+ * @param {Array<number|string>} [xTicks] - X-axis tick values for vertical lines, necessary if `includeVertical` is true.
+ *
+ * Behavior:
+ *  - Renders horizontal grid lines based on the `ticks` & scale functions provided by the parent chart component.
+ *  - Vertical grid lines are experimental and can be enabled with `includeVertical` set to true.
+ *    However, their scaling and positioning may not be accurate relative to XAxis component (if used).
+ *
+ * Usage:
+ *  <Chart ... >
+ *    <CustomGrid />
+ *  </Chart>
+ *
+ * Note: Use `includeVertical` cautiously; vertical lines are not fully developed.
+ */
+export const CustomGrid: React.FC<Partial<CustomGridProps>> = ({
+  x,
+  y,
+  ticks,
+  xTicks,
+  includeVertical = false
+}) => {
   const [firstTick, ...remainingTicks] = ticks;
   const dashArray = [1, 3];
   const strokeSolidWidth = 0.2;
@@ -16,7 +47,7 @@ export const CustomGrid: React.FC<Partial<CustomGridProps>> = ({ y, ticks }) =>
   const strokeDashWidth = 1;
   const strokeDashColor = colors.lightGrey;
 
-  const renderLine = (tick: number, stroke: string, strokeWidth: number, dashArray?: number[]) => (
+  const renderHorizontalLine = (tick: number, stroke: string, strokeWidth: number, dashArray?: number[]) => (
     <Line
       key={`line-${tick}`}
       x1="0%"
@@ -29,10 +60,29 @@ export const CustomGrid: React.FC<Partial<CustomGridProps>> = ({ y, ticks }) =>
     />
   );
 
+  const topY = y(Math.max(...ticks));
+  const bottomY = y(Math.min(...ticks));
+  const renderVerticalLine = (tick: number, stroke: string, strokeWidth: number, dashArray?: number[]) => {
+    return (
+      <Line
+        key={`vertical-line-${tick}`}
+        x1={x(tick)}
+        x2={x(tick)}
+        y1={topY}
+        y2={bottomY}
+        stroke={stroke}
+        strokeWidth={strokeWidth}
+        strokeDasharray={dashArray}
+      />
+    );
+  };
+
+
   return (
     <G>
-      {renderLine(firstTick, strokeSolidColor, strokeSolidWidth)}
-      {remainingTicks.map((tick) => renderLine(tick, strokeDashColor, strokeDashWidth, dashArray))}
+      {renderHorizontalLine(firstTick, strokeSolidColor, strokeSolidWidth)}
+      {remainingTicks.map((tick) => renderHorizontalLine(tick, strokeDashColor, strokeDashWidth, dashArray))}
+      {includeVertical && xTicks.map((_, index) => renderVerticalLine(index, strokeDashColor, strokeDashWidth, dashArray))}
     </G>
   );
 };