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import { createCanvas } from "https://deno.land/x/canvas/mod.ts";
import * as chartjs from 'https://cdn.skypack.dev/chart.js';

function once(f) {
  let executed = false;
  return () => {
    if (executed) return;
    executed = true;
    f();
  };
}

// Init ChartJS globals
const globalInit = once(() => chartjs.Chart.register(...chartjs.registerables));

class DenoPlatform extends chartjs.BasePlatform {
  acquireContext(canvas, _) {
    return canvas.getContext("2d");
  }
}

export function render(width, height, chartjsConfig, imageType="image/png") {
  // Init globals once
  globalInit();
  // Create canvas
  const canvas = createCanvas(width, height);
  // Patch options
  chartjsConfig.options = chartjsConfig.options || {};
  chartjsConfig.options.responsive = false;
  chartjsConfig.options.animation = false;
  // Temporarily patch console.error, since we'll fail with
  // console.error("Failed to create chart: can't acquire context from the given item");
  // due to ctx not having a .canvas attribute
  const oldConsoleError = globalThis.console.error;
  globalThis.console.error = () => {};
  // Init chart, expect to fail
  const chart = new chartjs.Chart(
    canvas,
    {
      ...chartjsConfig,
      platform: DenoPlatform,
    },
  );
  // Restore console.error
  globalThis.console.error = oldConsoleError;
  // Finish init: set canvas, width & height
  chart.canvas = canvas;
  chart.width = width;
  chart.height = height;
  // Do render
  chart._initialize();
  chart.update();
  
  return canvas.toBuffer(imageType);
}