import * as React from 'react';
import { LayoutRectangle, View } from 'react-native';

import { NativeLinearGradientPoint, NativeLinearGradientProps } from './NativeLinearGradient.types';
import { normalizeColor } from './normalizeColor';

export default function NativeLinearGradient({
  colors,
  locations,
  startPoint,
  endPoint,
  ...props
}: NativeLinearGradientProps): React.ReactElement {
  const [layout, setLayout] = React.useState<LayoutRectangle | null>(null);

  const { width = 1, height = 1 } = layout ?? {};

  // TODO(Bacon): In the future we could consider adding `backgroundRepeat: "no-repeat"`. For more
  // browser support.
  const linearGradientBackgroundImage = React.useMemo(() => {
    return getLinearGradientBackgroundImage(colors, locations, startPoint, endPoint, width, height);
  }, [colors, locations, startPoint, endPoint, width, height]);

  return (
    <View
      {...props}
      style={[
        props.style,
        // @ts-ignore: [ts] Property 'backgroundImage' does not exist on type 'ViewStyle'.
        { backgroundImage: linearGradientBackgroundImage },
      ]}
      onLayout={(event) => {
        const { x, y, width, height } = event.nativeEvent.layout;
        const oldLayout = layout ?? { x: 0, y: 0, width: 1, height: 1 };
        // don't set new layout state unless the layout has actually changed
        if (
          x !== oldLayout.x ||
          y !== oldLayout.y ||
          width !== oldLayout.width ||
          height !== oldLayout.height
        ) {
          setLayout({ x, y, width, height });
        }

        if (props.onLayout) {
          props.onLayout(event);
        }
      }}
    />
  );
}

/**
 * Extracted to a separate function in order to be able to test logic independently.
 */
export function getLinearGradientBackgroundImage(
  colors: number[] | string[],
  locations?: number[] | null,
  startPoint?: NativeLinearGradientPoint | null,
  endPoint?: NativeLinearGradientPoint | null,
  width: number = 1,
  height: number = 1
) {
  const gradientColors = calculateGradientColors(colors, locations);
  const angle = calculatePseudoAngle(width, height, startPoint, endPoint);
  return `linear-gradient(${angle}deg, ${gradientColors.join(', ')})`;
}

function calculatePseudoAngle(
  width: number,
  height: number,
  startPoint?: NativeLinearGradientPoint | null,
  endPoint?: NativeLinearGradientPoint | null
) {
  const getControlPoints = (): NativeLinearGradientPoint[] => {
    let correctedStartPoint: NativeLinearGradientPoint = [0, 0];
    if (Array.isArray(startPoint)) {
      correctedStartPoint = [
        startPoint[0] != null ? startPoint[0] : 0.0,
        startPoint[1] != null ? startPoint[1] : 0.0,
      ];
    }
    let correctedEndPoint: NativeLinearGradientPoint = [0.0, 1.0];
    if (Array.isArray(endPoint)) {
      correctedEndPoint = [
        endPoint[0] != null ? endPoint[0] : 0.0,
        endPoint[1] != null ? endPoint[1] : 1.0,
      ];
    }
    return [correctedStartPoint, correctedEndPoint];
  };

  const [start, end] = getControlPoints();
  start[0] *= width;
  end[0] *= width;
  start[1] *= height;
  end[1] *= height;
  const py = end[1] - start[1];
  const px = end[0] - start[0];

  return 90 + (Math.atan2(py, px) * 180) / Math.PI;
}

function calculateGradientColors(colors: number[] | string[], locations?: number[] | null) {
  return colors.map((color: number | string, index: number): string | void => {
    const hexColor = normalizeColor(color);
    let output = hexColor;
    if (locations && locations[index]) {
      const location = Math.max(0, Math.min(1, locations[index]));
      // Convert 0...1 to 0...100
      const percentage = location * 100;
      output += ` ${percentage}%`;
    }
    return output;
  });
}