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import { Rectangle } from '@pixi/math';
import { RenderTexture, Texture } from '@pixi/core';
import { Sprite } from '@pixi/sprite';

import type { ColorStop } from './ColorStop';
import type { Renderer } from '@pixi/core';

/**
 * Converts a hexadecimal color into a CSS color string.
 * 
 * @ignore
 * @param color - The hexadecimal form of the color.
 */
function cssColor(color: number | string) {
    if(typeof color === 'string'){
        return color;
    }
    let string = color.toString(16);

    while (string.length < 6) {
        string = `0${string}`;
    }

    return `#${string}`;
}

const tempSourceFrame = new Rectangle();
const tempDestinationFrame = new Rectangle();

/**
 * Factory class for generating color-gradient textures.
 * 
 * @public
 */
export class GradientFactory
{
    /**
     * Renders a linear-gradient into `renderTexture` that starts from (x0, y0) and ends at (x1, y1). These
     * coordinates are defined in the **texture's space**. That means only the frame (0, 0, `renderTexture.width`, `renderTexture.height`)
     * will be rendered.
     * 
     * This method can be called inside a render cycle, and will preserve the renderer state. However, the current implementation
     * causes a batch renderer flush.
     * 
     * @param renderer - The renderer to use for drawing the gradient.
     * @param renderTexture - The texture to render the gradient into.
     * @param options - The gradient parameters.
     * @param options.x0 - The x-coordinate of the gradient's start point.
     * @param options.y0 - The y-coordinate of the gradient's start point.
     * @param options.x1 - The x-coordinate of the gradient's end point.
     * @param options.y1 - The y-coordinate of the gradient's end point.
     * @param options.colorStops - The color stops along the gradient pattern.
     * @todo This implementation is currently using the Canvas API (slow). It will be converted to a WebGL shader.
     * @todo This implementation causes a batch renderer flush. This will be optimized in a future release.
     */
    static createLinearGradient(
        renderer: Renderer, 
        renderTexture: RenderTexture, 
        options: {
            x0: number,
            y0: number,
            x1: number,
            y1: number,
            colorStops: ColorStop[]
        }
    ): RenderTexture
    {
        const { x0, y0, x1, y1, colorStops } = options;

        const canvas = document.createElement('canvas');

        canvas.width = renderTexture.width;
        canvas.height = renderTexture.height;

        const context = canvas.getContext('2d');

        const gradient = context.createLinearGradient(x0, y0, x1, y1);

        colorStops.forEach((stop) => {
            gradient.addColorStop(stop.offset, cssColor(stop.color));
        });

        context.fillStyle = gradient;
        context.fillRect(0, 0, renderTexture.width, renderTexture.height);

        // Store the current render-texture binding.
        const renderTarget = renderer.renderTexture.current;
        const sourceFrame = tempSourceFrame.copyFrom(renderer.renderTexture.sourceFrame);
        const destinationFrame = tempDestinationFrame.copyFrom(renderer.renderTexture.destinationFrame);

        const renderSprite = new Sprite(Texture.from(canvas));

        renderer.batch.flush();

        renderer.renderTexture.bind(renderTexture);
        renderSprite.render(renderer);
        
        renderer.batch.flush();
        renderer.renderTexture.bind(renderTarget, sourceFrame, destinationFrame);

        return renderTexture;
    }

    /**
     * Renders a radial-gradient into `renderTexture` that starts at the circle centered at (x0, y0) of radius r0 and
     * ends at the circle centered at (x1, y1) of radius r1.
     * 
     * This method can be called inside a render cycle, and will preserve the renderer state. However, the current implementation
     * causes a batch renderer flush.
     * 
     * @param renderer - The renderer to use for drawing the gradient.
     * @param renderTexture - The texture to render the gradient into.
     * @param options - The gradient parameters.
     * @param options.x0 - The x-coordinate of the starting circle's center.
     * @param options.y0 - The y-coordinate of the starting circle's center.
     * @param options.r0 - The radius of the starting circle.
     * @param options.x1 - The x-coordinate of the ending circle's center.
     * @param options.y1 - The y-coordinate of the ending circle's center.
     * @param options.colorStops - The color stops along the gradient pattern.
     * @todo This implementation is currently using the Canvas API (slow). It will be converted to a WebGL shader.
     * @todo This implementation causes a batch renderer flush. This will be optimized in a future release.
     */
    static createRadialGradient(
        renderer: Renderer, 
        renderTexture: RenderTexture, 
        options: {
            x0: number,
            y0: number,
            r0: number,
            x1: number,
            y1: number,
            r1: number,
            colorStops: ColorStop[]
        }
    ): RenderTexture
    {
        const { x0, y0, r0, x1, y1, r1, colorStops } = options;

        const canvas = document.createElement('canvas');

        canvas.width = renderTexture.width;
        canvas.height = renderTexture.height;

        const context = canvas.getContext('2d');

        const gradient = context.createRadialGradient(x0, y0, r0, x1, y1, r1);

        colorStops.forEach((stop) => {
            gradient.addColorStop(stop.offset, cssColor(stop.color));
        });

        context.fillStyle = gradient;
        context.fillRect(0, 0, renderTexture.width, renderTexture.height);

        // Store the current render-texture binding.
        const renderTarget = renderer.renderTexture.current;
        const sourceFrame = tempSourceFrame.copyFrom(renderer.renderTexture.sourceFrame);
        const destinationFrame = tempDestinationFrame.copyFrom(renderer.renderTexture.destinationFrame);

        const renderSprite = new Sprite(Texture.from(canvas));

        renderer.batch.flush();

        renderer.renderTexture.bind(renderTexture);
        renderSprite.render(renderer);
        
        renderer.batch.flush();
        renderer.renderTexture.bind(renderTarget, sourceFrame, destinationFrame);

        return renderTexture;
    }
}