"use client";

import { useEffect, useRef } from "react";
import { cn } from "@/lib/utils";

interface ShaderBackgroundProps {
  className?: string;
  opacity?: number;
}

const VS_SOURCE = `
  attribute vec4 aVertexPosition;
  void main() {
    gl_Position = aVertexPosition;
  }
`;

const FS_SOURCE = `
  precision highp float;
  uniform vec2 iResolution;
  uniform float iTime;

  const float overallSpeed = 0.2;
  const float gridSmoothWidth = 0.015;
  const float axisWidth = 0.05;
  const float majorLineWidth = 0.025;
  const float minorLineWidth = 0.0125;
  const float majorLineFrequency = 5.0;
  const float minorLineFrequency = 1.0;
  const vec4 gridColor = vec4(0.5);
  const float scale = 5.0;
  const vec4 lineColor = vec4(0.4, 0.2, 0.8, 1.0);
  const float minLineWidth = 0.01;
  const float maxLineWidth = 0.2;
  const float lineSpeed = 1.0 * overallSpeed;
  const float lineAmplitude = 1.0;
  const float lineFrequency = 0.2;
  const float warpSpeed = 0.2 * overallSpeed;
  const float warpFrequency = 0.5;
  const float warpAmplitude = 1.0;
  const float offsetFrequency = 0.5;
  const float offsetSpeed = 1.33 * overallSpeed;
  const float minOffsetSpread = 0.6;
  const float maxOffsetSpread = 2.0;
  const int linesPerGroup = 16;

  #define drawCircle(pos, radius, coord) smoothstep(radius + gridSmoothWidth, radius, length(coord - (pos)))
  #define drawSmoothLine(pos, halfWidth, t) smoothstep(halfWidth, 0.0, abs(pos - (t)))
  #define drawCrispLine(pos, halfWidth, t) smoothstep(halfWidth + gridSmoothWidth, halfWidth, abs(pos - (t)))
  #define drawPeriodicLine(freq, width, t) drawCrispLine(freq / 2.0, width, abs(mod(t, freq) - (freq) / 2.0))

  float drawGridLines(float axis) {
    return drawCrispLine(0.0, axisWidth, axis)
          + drawPeriodicLine(majorLineFrequency, majorLineWidth, axis)
          + drawPeriodicLine(minorLineFrequency, minorLineWidth, axis);
  }

  float drawGrid(vec2 space) {
    return min(1.0, drawGridLines(space.x) + drawGridLines(space.y));
  }

  float random(float t) {
    return (cos(t) + cos(t * 1.3 + 1.3) + cos(t * 1.4 + 1.4)) / 3.0;
  }

  float getPlasmaY(float x, float horizontalFade, float offset) {
    return random(x * lineFrequency + iTime * lineSpeed) * horizontalFade * lineAmplitude + offset;
  }

  void main() {
    vec2 fragCoord = gl_FragCoord.xy;
    vec4 fragColor;
    vec2 uv = fragCoord.xy / iResolution.xy;
    vec2 space = (fragCoord - iResolution.xy / 2.0) / iResolution.x * 2.0 * scale;

    float horizontalFade = 1.0 - (cos(uv.x * 6.28) * 0.5 + 0.5);
    float verticalFade = 1.0 - (cos(uv.y * 6.28) * 0.5 + 0.5);

    space.y += random(space.x * warpFrequency + iTime * warpSpeed) * warpAmplitude * (0.5 + horizontalFade);
    space.x += random(space.y * warpFrequency + iTime * warpSpeed + 2.0) * warpAmplitude * horizontalFade;

    vec4 lines = vec4(0.0);
    vec4 bgColor1 = vec4(0.1, 0.1, 0.3, 1.0);
    vec4 bgColor2 = vec4(0.3, 0.1, 0.5, 1.0);

    for(int l = 0; l < linesPerGroup; l++) {
      float normalizedLineIndex = float(l) / float(linesPerGroup);
      float offsetTime = iTime * offsetSpeed;
      float offsetPosition = float(l) + space.x * offsetFrequency;
      float rand = random(offsetPosition + offsetTime) * 0.5 + 0.5;
      float halfWidth = mix(minLineWidth, maxLineWidth, rand * horizontalFade) / 2.0;
      float offset = random(offsetPosition + offsetTime * (1.0 + normalizedLineIndex)) * mix(minOffsetSpread, maxOffsetSpread, horizontalFade);
      float linePosition = getPlasmaY(space.x, horizontalFade, offset);
      float line = drawSmoothLine(linePosition, halfWidth, space.y) / 2.0 + drawCrispLine(linePosition, halfWidth * 0.15, space.y);

      float circleX = mod(float(l) + iTime * lineSpeed, 25.0) - 12.0;
      vec2 circlePosition = vec2(circleX, getPlasmaY(circleX, horizontalFade, offset));
      float circle = drawCircle(circlePosition, 0.01, space) * 4.0;

      line = line + circle;
      lines += line * lineColor * rand;
    }

    fragColor = mix(bgColor1, bgColor2, uv.x);
    fragColor *= verticalFade;
    fragColor.a = 1.0;
    fragColor += lines;

    gl_FragColor = fragColor;
  }
`;

/**
 * @description Compile one shader source.
 * @see components/ui/shader-background.tsx ShaderBackground useEffect - WebGL init flow
 */
function loadShader(gl: WebGLRenderingContext, type: number, source: string) {
  const shader = gl.createShader(type);
  if (!shader) return null;

  gl.shaderSource(shader, source);
  gl.compileShader(shader);

  if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
    console.error("Shader compile error:", gl.getShaderInfoLog(shader));
    gl.deleteShader(shader);
    return null;
  }

  return shader;
}

/**
 * @description Create and link WebGL shader program.
 * @see components/ui/shader-background.tsx ShaderBackground useEffect - shader program setup
 */
function initShaderProgram(gl: WebGLRenderingContext, vertexSource: string, fragmentSource: string) {
  const vertexShader = loadShader(gl, gl.VERTEX_SHADER, vertexSource);
  const fragmentShader = loadShader(gl, gl.FRAGMENT_SHADER, fragmentSource);
  if (!vertexShader || !fragmentShader) return null;

  const shaderProgram = gl.createProgram();
  if (!shaderProgram) return null;

  gl.attachShader(shaderProgram, vertexShader);
  gl.attachShader(shaderProgram, fragmentShader);
  gl.linkProgram(shaderProgram);

  if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
    console.error("Shader program link error:", gl.getProgramInfoLog(shaderProgram));
    gl.deleteProgram(shaderProgram);
    return null;
  }

  return shaderProgram;
}

/**
 * @description Animated shader background canvas.
 * @param className Tailwind class for canvas.
 * @param opacity Canvas opacity.
 * @see https://21st.dev/community/components/thanh/shader-background/default
 */
const ShaderBackground = ({ className, opacity = 0.9 }: ShaderBackgroundProps) => {
  const canvasRef = useRef<HTMLCanvasElement | null>(null);

  useEffect(() => {
    const canvas = canvasRef.current;
    if (!canvas) return;

    const gl = canvas.getContext("webgl");
    if (!gl) {
      console.warn("WebGL not supported.");
      return;
    }

    const shaderProgram = initShaderProgram(gl, VS_SOURCE, FS_SOURCE);
    if (!shaderProgram) return;

    const positionBuffer = gl.createBuffer();
    if (!positionBuffer) return;

    gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
    const positions = [-1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0, 1.0];
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(positions), gl.STATIC_DRAW);

    const vertexPosition = gl.getAttribLocation(shaderProgram, "aVertexPosition");
    const resolution = gl.getUniformLocation(shaderProgram, "iResolution");
    const time = gl.getUniformLocation(shaderProgram, "iTime");

    const resizeCanvas = () => {
      const dpr = window.devicePixelRatio || 1;
      const nextWidth = Math.floor(window.innerWidth * dpr);
      const nextHeight = Math.floor(window.innerHeight * dpr);
      canvas.width = nextWidth;
      canvas.height = nextHeight;
      gl.viewport(0, 0, nextWidth, nextHeight);
    };

    window.addEventListener("resize", resizeCanvas);
    resizeCanvas();

    const startTime = Date.now();
    let frameId = 0;

    const render = () => {
      const currentTime = (Date.now() - startTime) / 1000;

      gl.clearColor(0.0, 0.0, 0.0, 1.0);
      gl.clear(gl.COLOR_BUFFER_BIT);
      gl.useProgram(shaderProgram);

      if (resolution) gl.uniform2f(resolution, canvas.width, canvas.height);
      if (time) gl.uniform1f(time, currentTime);

      gl.bindBuffer(gl.ARRAY_BUFFER, positionBuffer);
      gl.vertexAttribPointer(vertexPosition, 2, gl.FLOAT, false, 0, 0);
      gl.enableVertexAttribArray(vertexPosition);
      gl.drawArrays(gl.TRIANGLE_STRIP, 0, 4);

      frameId = requestAnimationFrame(render);
    };

    frameId = requestAnimationFrame(render);

    return () => {
      cancelAnimationFrame(frameId);
      window.removeEventListener("resize", resizeCanvas);
      gl.deleteBuffer(positionBuffer);
      gl.deleteProgram(shaderProgram);
    };
  }, []);

  return (
    <canvas
      ref={canvasRef}
      aria-hidden="true"
      className={cn("fixed inset-0 -z-10 h-full w-full", className)}
      style={{ opacity }}
    />
  );
};

export default ShaderBackground;