const canvas = document.getElementById("Matrix")
const context = canvas.getContext("2d")

canvas.height = window.innerHeight + 100;
canvas.width = window.innerWidth + 5;

const chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789./*-+#$%^@!~?><:;[]{}\」=_αβΓγΔδεζηΘθικΛλμΞξΠπρΣσςτυΦφχΨψΩω×≦≧≠∞≒≡～∩∠∪∟⊿∫∮∵∴＄￥〒￠￡℃€℉╩◢ⅩⅨⅧⅦⅥⅤⅣⅢⅡⅠあいうえおがぎぐげござじずぜぞだぢつでづどにぬのばひぴぶへぺぼみゃょァゐゎè";

const fontSize = 16;
const columns = canvas.width / fontSize; 

const charArr = [];
for(let i = 0; i < columns; ++i) {
  charArr[i] = 1;
}

let frame = 0;
let str;

context.fillStyle = "rgba(0, 0, 0, 1)";
context.fillRect(0, 0, canvas.width, canvas.height);

function Update() {
  context.fillStyle = "rgba(0, 0, 0, 0.05)";
  context.fillRect(0, 0, canvas.width, canvas.height);
  if(frame == 0){
    let a = parseInt(Math.random() * 255);
    str = `rgba(${a}, ${Math.abs(a - 127)}, ${Math.abs(a - 255)}, 0.9)`;
  }
  context.fillStyle = str;
  context.font = fontSize + "px monospace";
  
  for(let i = 0; i < columns; ++i){
    const text = chars[Math.floor(Math.random() * chars.length)];
    context.fillText(text, i * fontSize, charArr[i] * fontSize);
    if(charArr[i] * fontSize > canvas.height && Math.random() > 0.90){
      charArr[i] = 0;
    }
    charArr[i]++;
  }
  frame++;
  if(frame <= 40 * (Math.floor(Math.random() * 10) + 3)) requestAnimationFrame(Update); // 40 frames a cycle
  else{
    frame = 0;
    Appear();
  }
}