// WebGL Newton fractal renderer (z^3 - 1, ocean palette)
// Ported from crates/fractal-engine/src/{newton.rs, color.rs}

function initFractal(canvasId) {
  var canvas = document.getElementById(canvasId);
  if (!canvas) return;

  var gl = canvas.getContext('webgl') || canvas.getContext('experimental-webgl');
  if (!gl) {
    // Fallback: ocean-themed CSS gradient
    canvas.style.background =
      'radial-gradient(ellipse at center, #0d3842 0%, #0c2e58 40%, #060a10 100%)';
    return;
  }

  // --- Shaders ---

  var VERT_SRC = [
    'attribute vec2 a_pos;',
    'void main() { gl_Position = vec4(a_pos, 0.0, 1.0); }'
  ].join('\n');

  var FRAG_SRC = [
    'precision highp float;',
    'uniform float u_time;',
    'uniform vec2 u_resolution;',
    '',
    'void main() {',
    '    vec2 uv = gl_FragCoord.xy / u_resolution;',
    '    float aspect = u_resolution.x / u_resolution.y;',
    '',
    '    // Map to complex plane (view_size=3.0, centered)',
    '    float zr = (uv.x - 0.5) * 3.0 * aspect;',
    '    float zi = (uv.y - 0.5) * 3.0;',
    '',
    '    // Rotate by time (animation)',
    '    float ct = cos(u_time);',
    '    float st = sin(u_time);',
    '    float tmp = zr * ct - zi * st;',
    '    zi = zr * st + zi * ct;',
    '    zr = tmp;',
    '',
    '    // Newton iteration for z^3 - 1',
    '    int rootIndex = 0;',
    '    int iters = 0;',
    '    for (int i = 0; i < 32; i++) {',
    '        iters = i;',
    '        float zr2 = zr*zr - zi*zi;',
    '        float zi2 = 2.0*zr*zi;',
    '        float zr3 = zr*zr2 - zi*zi2;',
    '        float zi3 = zr*zi2 + zi*zr2;',
    '',
    '        float d0 = (zr-1.0)*(zr-1.0) + zi*zi;',
    '        float d1 = (zr+0.5)*(zr+0.5) + (zi-0.866025)*(zi-0.866025);',
    '        float d2 = (zr+0.5)*(zr+0.5) + (zi+0.866025)*(zi+0.866025);',
    '',
    '        if (d0 < 1e-6) { rootIndex = 0; break; }',
    '        if (d1 < 1e-6) { rootIndex = 1; break; }',
    '        if (d2 < 1e-6) { rootIndex = 2; break; }',
    '',
    '        float nr = zr3 - 1.0;',
    '        float ni = zi3;',
    '        float dr = 3.0*zr2;',
    '        float di = 3.0*zi2;',
    '        float denom = dr*dr + di*di;',
    '        if (denom < 1e-12) break;',
    '        zr -= (nr*dr + ni*di) / denom;',
    '        zi -= (ni*dr - nr*di) / denom;',
    '    }',
    '',
    '    // Fallback: closest root',
    '    float d0 = (zr-1.0)*(zr-1.0) + zi*zi;',
    '    float d1 = (zr+0.5)*(zr+0.5) + (zi-0.866025)*(zi-0.866025);',
    '    float d2 = (zr+0.5)*(zr+0.5) + (zi+0.866025)*(zi+0.866025);',
    '    if (d1 < d0 && d1 < d2) rootIndex = 1;',
    '    else if (d2 < d0) rootIndex = 2;',
    '',
    '    // Ocean palette',
    '    float brightness = max(1.0 - float(iters)/32.0 * 0.7, 0.3);',
    '    vec3 color;',
    '    if (rootIndex == 0) color = vec3(0.05, 0.25, 0.55);',
    '    else if (rootIndex == 1) color = vec3(0.0, 0.45, 0.50);',
    '    else color = vec3(0.15, 0.55, 0.65);',
    '',
    '    gl_FragColor = vec4(color * brightness, 1.0);',
    '}'
  ].join('\n');

  // --- Compile helpers ---

  function compile(type, src) {
    var s = gl.createShader(type);
    gl.shaderSource(s, src);
    gl.compileShader(s);
    if (!gl.getShaderParameter(s, gl.COMPILE_STATUS)) {
      console.error('Shader compile error:', gl.getShaderInfoLog(s));
      return null;
    }
    return s;
  }

  var vs = compile(gl.VERTEX_SHADER, VERT_SRC);
  var fs = compile(gl.FRAGMENT_SHADER, FRAG_SRC);
  if (!vs || !fs) return;

  var prog = gl.createProgram();
  gl.attachShader(prog, vs);
  gl.attachShader(prog, fs);
  gl.linkProgram(prog);
  if (!gl.getProgramParameter(prog, gl.LINK_STATUS)) {
    console.error('Program link error:', gl.getProgramInfoLog(prog));
    return;
  }
  gl.useProgram(prog);

  // --- Full-screen triangle ---

  var buf = gl.createBuffer();
  gl.bindBuffer(gl.ARRAY_BUFFER, buf);
  gl.bufferData(gl.ARRAY_BUFFER, new Float32Array([-1,-1, 3,-1, -1,3]), gl.STATIC_DRAW);

  var aPos = gl.getAttribLocation(prog, 'a_pos');
  gl.enableVertexAttribArray(aPos);
  gl.vertexAttribPointer(aPos, 2, gl.FLOAT, false, 0, 0);

  var uTime = gl.getUniformLocation(prog, 'u_time');
  var uRes  = gl.getUniformLocation(prog, 'u_resolution');

  // --- Resize ---

  function resize() {
    canvas.width  = window.innerWidth;
    canvas.height = window.innerHeight;
    gl.viewport(0, 0, canvas.width, canvas.height);
  }
  resize();
  window.addEventListener('resize', resize);

  // --- Animation loop ---

  var startTime = performance.now();
  var animationSpeed = 0.0001;

  function frame() {
    var t = (performance.now() - startTime) * animationSpeed;
    gl.uniform1f(uTime, t);
    gl.uniform2f(uRes, canvas.width, canvas.height);
    gl.drawArrays(gl.TRIANGLES, 0, 3);
    requestAnimationFrame(frame);
  }
  requestAnimationFrame(frame);
}