"use strict";

var canvas, ctx;

// Not jQuery
function $(id) {
  return document.getElementById(id);
}

var downloadCount = 0;

function downloadImage() {
  const link = document.createElement("a");
  link.download = `image${downloadCount}.png`;
  link.href = $("viewport").toDataURL();
  link.click();
  downloadCount++;
}

function getDrawingParameters() {
  let angle = Number($("angle").value);
  const bandCount = Number($("band-count").value);
  // Convert to radians
  angle = angle * (Math.PI / 180);

  const start = $("starting-color");
  const end = $("ending-color");
  const dynamicWidth = $("dynamic-width").checked;
  const startingColor = parseHexColor(start.value);
  const endingColor = parseHexColor(end.value);
  return { startingColor, endingColor, dynamicWidth, bandCount, angle };
}

// Setup, and register events
document.addEventListener("DOMContentLoaded", () => {
  // Check URL for parameters
  parseURLParams();

  canvas = $("viewport");
  ctx = canvas.getContext("2d");
  ctx.translate(canvas.width / 2, canvas.height / 2);
  ctx.imageSmoothingEnabled = false;

  const watchIds = [
    "starting-color",
    "ending-color",
    "band-count",
    "band-count-number",
    "angle",
    "angle-number",
    "dynamic-width",
  ];
  const LinkedInputs = [
    ["angle", "angle-number"],
    ["band-count", "band-count-number"],
  ];

  // Link inputs
  LinkedInputs.forEach((ids) => {
    const [inputA, inputB] = ids.map((id) => $(id));
    inputB.value = inputA.value;
    inputA.addEventListener("input", () => {
      inputB.value = inputA.value;
    });
    inputB.addEventListener("input", () => {
      inputA.value = inputB.value;
    });
  });

  // Watch inputs
  watchIds.forEach((id) => {
    $(id).addEventListener("input", () => {
      drawParamUpdated();
    });
  });

  //Watch random color button
  $("randomize-colors").addEventListener("click", () => {
    $("starting-color").value = randomHexColor();
    $("ending-color").value = randomHexColor();
    drawParamUpdated();
  });

  // Watch download button
  $("download-image").addEventListener("click", () => {
    downloadImage();
  });

  // Watch copy link button
  $("copy-link").addEventListener("click", () => {
    const url = encodeShareURL();
    const linkCopyIndicator = $("link-copy-indicator");
    linkCopyIndicator.textContent = url;
    linkCopyIndicator.href = url;
    $("link-copy-infobox").style.display = "";
    navigator.clipboard.writeText(url);
  });

  drawImage(getDrawingParameters());
});

function drawParamUpdated() {
  $("link-copy-infobox").style.display = "none";
  drawImage(getDrawingParameters());
}

function drawImage({
  startingColor,
  endingColor,
  dynamicWidth,
  bandCount,
  angle,
}) {
  const canvasWidth = canvas.width;
  let drawWidth;
  // Rotating the bands will leave unfilled space in the corners.
  // Optionally, all bands can be scaled such that the entire space is filled with bands evenly.
  if (!dynamicWidth) {
    drawWidth = canvasWidth;
  } else if (angle < 0) {
    drawWidth = canvasWidth * Math.cos(angle + Math.PI / 4) * 2 * Math.SQRT1_2;
  } else {
    drawWidth = canvasWidth * Math.sin(angle + Math.PI / 4) * 2 * Math.SQRT1_2;
  }

  const stepIncrementWidth = drawWidth / bandCount;
  const incrementColor = {
    red: (endingColor.red - startingColor.red) / (bandCount - 1),
    green: (endingColor.green - startingColor.green) / (bandCount - 1),
    blue: (endingColor.blue - startingColor.blue) / (bandCount - 1),
  };
  const h_w = drawWidth / 2;
  const rotate = newRotator(angle);
  // Draw a bunch of rectangular bands.
  // Each rectangle is defined to be vertical, and further to the right than the last.
  // Rotation of the rectangles is taken care of separately.
  for (let bandNo = 0; bandNo < bandCount; bandNo++) {
    const red = startingColor.red + incrementColor.red * bandNo;
    const green = startingColor.green + incrementColor.green * bandNo;
    const blue = startingColor.blue + incrementColor.blue * bandNo;

    ctx.fillStyle = `rgb(${red},${green},${blue})`;

    // `magic` is added to the points to make the bands continue on out when dynamicWidth is disabled
    // magic was found by trial and error.
    // I reckon there's a more mathematical method to find it, but 4.75 seems to fill the screen for all cases.
    const magic = 4.75 * canvasWidth;

    const point1 = [bandNo * stepIncrementWidth - h_w - 1, -h_w - magic];
    const point2 = [(bandNo + 1) * stepIncrementWidth - h_w, -h_w - magic];
    const point3 = [(bandNo + 1) * stepIncrementWidth - h_w, h_w + magic];
    const point4 = [bandNo * stepIncrementWidth - h_w - 1, h_w + magic];

    // If dynamic width is disabled, make the first and last bands wider such that no black space is left
    if (!dynamicWidth) {
      // magic2 is again a magic number found by trial and error. I wasn't in a mood for trigonometry on the day I wrote this.
      const magic2 = canvasWidth * 4.85;
      if (bandNo === 0) {
        point1[0] -= magic2;
        point4[0] -= magic2;
      } else if (bandNo === bandCount - 1) {
        point2[0] += magic2;
        point2[0] += magic2;
      }
    }

    // Draw polygon with above points, rotated
    ctx.beginPath();
    ctx.moveTo(...rotate(point1));
    ctx.lineTo(...rotate(point2));
    ctx.lineTo(...rotate(point3));
    ctx.lineTo(...rotate(point4));
    ctx.closePath();
    ctx.fill();
  }
}

// Vector rotation but with cached sine and cosine values to greatly improve performance
function newRotator(angleRad) {
  const cos = Math.cos(angleRad);
  const sin = Math.sin(angleRad);
  // Rotation using matrix math
  // https://en.wikipedia.org/wiki/Rotation_matrix
  return function rotate([x, y]) {
    return [x * cos - y * sin, x * sin + y * cos];
  };
}

// Take a hexadecimal color input like "#abcd61" and convert it into Red, Green, and Blue color values
function parseHexColor(hexColorStr) {
  if (hexColorStr.length !== 7) return false;
  if (hexColorStr.substr(0, 1) !== "#") return false;
  // Remove hash from beginning of string
  const hexDigits = hexColorStr.substr(1, 6);

  // Isolate colors into substrings
  const redDigits = hexDigits.substr(0, 2);
  const greenDigits = hexDigits.substr(2, 2);
  const blueDigits = hexDigits.substr(4, 2);

  // Convert colors to numbers, from hexadecimal
  const red = parseInt(redDigits, 16);
  const green = parseInt(greenDigits, 16);
  const blue = parseInt(blueDigits, 16);

  return { red, green, blue };
}

function randomHexColor() {
  const randomHex = () =>
    Math.round(Math.random() * 255)
      .toString(16)
      .padStart(2, "0");
  return `#${randomHex()}${randomHex()}${randomHex()}`;
}

function RGBtoHexColor({ red, green, blue }) {
  return `#${red.toString(16).padStart(2)}${green
    .toString(16)
    .padStart(2)}${blue.toString(16).padStart(2)}`;
}

function encodeShareURL() {
  const dParams = getDrawingParameters();
  // Convert drawing parameters into efficient, URL encodable form
  // Substring to remove the initial '#'
  dParams.startingColor = RGBtoHexColor(dParams.startingColor).substring(1, 7);
  dParams.endingColor = RGBtoHexColor(dParams.endingColor).substring(1, 7);
  dParams.dynamicWidth = dParams.dynamicWidth ? 1 : 0;
  dParams.angle *= 180 / Math.PI;
  dParams.angle = Math.round(dParams.angle * 100) / 100;

  const URLparameters = `c1=${dParams.startingColor}&c2=${dParams.endingColor}&a=${dParams.angle}&b=${dParams.bandCount}&d=${dParams.dynamicWidth}`;
  const fullURL = new URL(window.origin);
  fullURL.pathname = location.pathname;
  fullURL.search = URLparameters;

  return fullURL;
}

function parseURLParams() {
  const urlSearchSlug = window.location.search;
  const fullParameterString = urlSearchSlug.split("?")[1];

  if (fullParameterString === undefined) {
    return;
  }
  const parameterMap = {};
  fullParameterString
    .split("&")
    .map((p) => p.split("="))
    .forEach((p) => {
      if (p.length == 2) {
        parameterMap[p[0]] = p[1];
      }
    });

  const parameterCount = Object.keys(parameterMap).length;
  if (parameterCount === 0) {
    return;
  }

  console.log(`Parsed ${parameterCount}, URL parameter(s)`, parameterMap);
  if ("a" in parameterMap) {
    const value = parseInt(parameterMap.a, 10);
    if (!isNaN(value)) {
      $("angle").value = value;
    }
  }
  if ("b" in parameterMap) {
    const value = parseInt(parameterMap.b, 10);
    if (!isNaN(value)) {
      $("band-count").value = value;
    }
  }
  if ("c1" in parameterMap) {
    $("starting-color").value = `#${parameterMap.c1}`;
  }
  if ("c2" in parameterMap) {
    $("ending-color").value = `#${parameterMap.c2}`;
  }
  if ("d" in parameterMap) {
    const dynamicWidthCheckbox = $("dynamic-width");

    dynamicWidthCheckbox.checked = parameterMap.d === "1";
  }
}