// PROCITY Lane D — impostor atlas + instanced billboard layer (the mid-tier LOD).
//
// Rigged mixers are expensive, so past ~25m a citizen becomes a flat billboard. To keep the mid
// crowd automatically in sync with the fleet, we render each ped ONCE to an offscreen render target
// from 4 yaw angles → one sprite atlas → an InstancedMesh of camera-facing quads that each pick the
// atlas cell for its nearest baked angle. One draw call for the entire mid crowd, per atlas.
//
// Cylindrical billboard (locked upright, rotates around Y toward the camera). No per-frame CPU
// matrix math beyond writing instance translation/scale + the chosen uv-offset.

import * as THREE from 'three';

// ---- bake: subjects[] (each { object3D, height }) × yaws → one atlas texture on a WebGLRenderTarget.
// Returns an atlas descriptor; keep it for the layer, call dispose() when done with the crowd.
export function bakeImpostorAtlas(renderer, subjects, { yaws = 4, cell = 128, maxTex = 2048, environment = null } = {}) {
  const n = subjects.length;
  const total = n * yaws;
  const cols = Math.max(1, Math.min(total, Math.floor(maxTex / cell)));
  const rows = Math.ceil(total / cols);
  const atlasW = cols * cell, atlasH = rows * cell;

  const rt = new THREE.WebGLRenderTarget(atlasW, atlasH, {
    minFilter: THREE.LinearFilter, magFilter: THREE.LinearFilter,
    format: THREE.RGBAFormat, generateMipmaps: false, depthBuffer: true,
  });
  // store LINEAR lit colour (no tone-map, no OETF) — the layer shader tone-maps + sRGB-encodes so
  // impostors match the ACES-tonemapped rigs exactly (seamless near↔mid). See IMP_FRAG.
  rt.texture.colorSpace = THREE.LinearSRGBColorSpace;
  const exposure = renderer.toneMappingExposure;

  // a tiny bake scene lit to roughly match a warm street key so impostors read like the rigs.
  // the environment (PMREM) matters: the peds are metallic-PBR and render dark without one.
  const scene = new THREE.Scene();
  scene.environment = environment;
  const key = new THREE.DirectionalLight(0xfff2e0, 2.1); key.position.set(0.6, 1.4, 0.9); scene.add(key);
  scene.add(new THREE.HemisphereLight(0xbfd4ff, 0x50463a, 1.2));
  const holder = new THREE.Group(); scene.add(holder);

  const cam = new THREE.OrthographicCamera(-1, 1, 1, -1, 0.01, 100);

  // preserve renderer state
  const prevRT = renderer.getRenderTarget();
  const prevAutoClear = renderer.autoClear;
  const prevClear = new THREE.Color(); renderer.getClearColor(prevClear);
  const prevAlpha = renderer.getClearAlpha();
  const prevScissorTest = renderer.getScissorTest();
  const prevToneMapping = renderer.toneMapping;
  const prevViewport = new THREE.Vector4(); renderer.getViewport(prevViewport);
  const prevScissor = new THREE.Vector4(); renderer.getScissor(prevScissor);
  renderer.toneMapping = THREE.NoToneMapping;   // bake linear; the shader tone-maps at display time

  renderer.setRenderTarget(rt);
  renderer.setClearColor(0x000000, 0);
  renderer.clear();                     // one clear to transparent, then paint cells without clearing
  renderer.autoClear = false;
  renderer.setScissorTest(true);

  // square framing (frustum aspect MUST equal the square cell or the figure stretches). The cell
  // frames a square world region 1.14h tall, from y=-0.07h (below the feet) to y=1.07h (headroom).
  const SPAN = 1.14, FOOT = 0.07;
  for (let s = 0; s < n; s++) {
    const subj = subjects[s];
    const obj = subj.object3D;
    const h = subj.height || 1.9;
    const half = h * SPAN * 0.5;              // square: half-width == half-height
    cam.left = -half; cam.right = half;
    cam.top = h * (SPAN - FOOT); cam.bottom = -h * FOOT;   // total height = h*SPAN, feet at world y=0
    cam.position.set(0, h * 0.5, -h * 4);     // camera on -Z, looking toward +Z (unit y=0 = feet)
    cam.lookAt(0, h * 0.5, 0);
    cam.updateProjectionMatrix();

    holder.clear();
    holder.add(obj);
    obj.position.set(0, 0, 0);

    for (let y = 0; y < yaws; y++) {
      obj.rotation.y = (y / yaws) * Math.PI * 2;   // bake evenly-spaced yaws; y=0 faces the camera
      obj.updateWorldMatrix(true, true);
      const k = s * yaws + y;
      const col = k % cols, row = (k / cols) | 0;
      // WebGL viewport/scissor origin is bottom-left
      const px = col * cell, py = atlasH - (row + 1) * cell;
      renderer.setViewport(px, py, cell, cell);
      renderer.setScissor(px, py, cell, cell);
      renderer.render(scene, cam);
    }
    holder.remove(obj);
  }

  // restore renderer
  renderer.setScissorTest(prevScissorTest);
  renderer.setViewport(prevViewport);           // per-cell setViewport clobbered these — restore both
  renderer.setScissor(prevScissor);
  renderer.autoClear = prevAutoClear;
  renderer.setClearColor(prevClear, prevAlpha);
  renderer.setRenderTarget(prevRT);
  renderer.toneMapping = prevToneMapping;

  return {
    texture: rt.texture, rt, yaws, cols, rows, n, exposure,
    frame: { span: SPAN, foot: FOOT },   // billboard sizing must match the bake framing
    cellScale: new THREE.Vector2(1 / cols, 1 / rows),
    // uv min corner (top-left in texture space) for a (subject, yaw) cell
    cellUV(s, y) {
      const k = s * yaws + y;
      const col = k % cols, row = (k / cols) | 0;
      return [col / cols, 1 - (row + 1) / rows];
    },
    dispose() { rt.dispose(); },
  };
}

// ---- the instanced billboard layer ----
const IMP_VERT = `
  attribute vec2 iUvOffset;
  uniform vec2 uCellScale;
  varying vec2 vUv;
  void main() {
    vUv = iUvOffset + uv * uCellScale;
    // instance translation + non-uniform scale (x = width, y = height) live in instanceMatrix.
    // Fold in modelMatrix so impostors track the citizens group's transform (chunk offsets in Lane B),
    // exactly like the rig children do — cameraPosition is world space, so the base must be too.
    vec3 base = (modelMatrix * vec4(instanceMatrix[3][0], instanceMatrix[3][1], instanceMatrix[3][2], 1.0)).xyz;
    float w = length(vec3(instanceMatrix[0][0], instanceMatrix[0][1], instanceMatrix[0][2]));
    float h = length(vec3(instanceMatrix[1][0], instanceMatrix[1][1], instanceMatrix[1][2]));
    vec3 toCam = cameraPosition - base;
    vec3 toCamH = normalize(vec3(toCam.x, 0.0, toCam.z));
    vec3 right = normalize(cross(vec3(0.0, 1.0, 0.0), toCamH)); // camera-right, horizontal
    vec3 up = vec3(0.0, 1.0, 0.0);
    vec3 world = base + right * (position.x * w) + up * (position.y * h);
    gl_Position = projectionMatrix * viewMatrix * vec4(world, 1.0);
  }
`;
// The atlas holds LINEAR lit colour. We output linear and let three's own pipeline tone-map +
// colour-manage via the injected chunks, so the impostor behaves EXACTLY like every other material:
//  • direct-to-canvas (test page): three applies ACES + sRGB (matches the near rigs)
//  • EffectComposer (shell): the RenderPass renders to a target → three uses NoToneMapping → we
//    output linear → OutputPass applies ACES once (matches the rigs). A self-tone-mapping shader
//    (toneMapped:false + in-shader ACES) would DOUBLE tone-map under the composer's OutputPass —
//    correct only on the canvas path. Letting three do it is right on both. (Exposure is global via
//    renderer.toneMappingExposure, so no per-material exposure plumbing is needed.)
// NOTE: three injects tonemapping_pars_fragment + colorspace_pars_fragment into the ShaderMaterial
// prefix automatically (WebGLProgram), so we include ONLY the call-sites here — adding the *_pars_*
// ourselves would double-define RRTAndODTFit etc. and fail to compile. <tonemapping_fragment> is a
// no-op when the render target forces NoToneMapping (composer RenderPass), and applies ACES on the
// canvas — exactly the behaviour that keeps impostors matched to the rigs on both paths.
const IMP_FRAG = `
  uniform sampler2D uAtlas;
  uniform vec3 uTint;
  varying vec2 vUv;
  void main() {
    vec4 c = texture2D(uAtlas, vUv);
    if (c.a < 0.5) discard;               // hard cut-out — no sorting needed
    gl_FragColor = vec4(c.rgb * uTint, 1.0);   // c.rgb is LINEAR
    #include <tonemapping_fragment>
    #include <colorspace_fragment>
  }
`;

export class ImpostorLayer {
  constructor(atlas, { maxInstances = 256 } = {}) {
    this.atlas = atlas;
    this.max = maxInstances;

    // unit quad, origin at bottom-centre (x in [-0.5,0.5], y in [0,1]) so it plants on the ground
    const geo = new THREE.PlaneGeometry(1, 1);
    geo.translate(0, 0.5, 0);
    const iGeo = new THREE.InstancedBufferGeometry();
    iGeo.index = geo.index;
    iGeo.attributes.position = geo.attributes.position;
    iGeo.attributes.uv = geo.attributes.uv;
    this._uvOffset = new THREE.InstancedBufferAttribute(new Float32Array(maxInstances * 2), 2);
    this._uvOffset.setUsage(THREE.DynamicDrawUsage);
    iGeo.setAttribute('iUvOffset', this._uvOffset);

    this.material = new THREE.ShaderMaterial({
      vertexShader: IMP_VERT, fragmentShader: IMP_FRAG,
      uniforms: {
        uAtlas: { value: atlas.texture },
        uCellScale: { value: atlas.cellScale },
        uTint: { value: new THREE.Color(1, 1, 1) },
      },
      transparent: false, side: THREE.DoubleSide,
      toneMapped: true,    // three tone-maps (canvas: ACES; composer: linear→OutputPass). See IMP_FRAG.
    });

    this.mesh = new THREE.InstancedMesh(iGeo, this.material, maxInstances);
    this.mesh.frustumCulled = false;      // we cull citizens ourselves; billboards span chunks
    this.mesh.count = 0;
    this.mesh.instanceMatrix.setUsage(THREE.DynamicDrawUsage);

    this._m = new THREE.Matrix4();
    this._q = new THREE.Quaternion();
    this._s = new THREE.Vector3();
    this._p = new THREE.Vector3();
  }

  // pick the baked yaw whose view best matches how the camera sees this citizen's facing.
  // facing = the citizen's heading angle (atan2(-dx,-dz) convention, matches rig fig.rotation.y).
  _yawIndex(x, z, facing, camX, camZ) {
    // ped forward (world) for heading `facing`: (-sin, -cos)
    const fx = -Math.sin(facing), fz = -Math.cos(facing);
    // ped→camera (horizontal)
    let cx = camX - x, cz = camZ - z;
    const len = Math.hypot(cx, cz) || 1; cx /= len; cz /= len;
    // signed angle from forward to ped→cam, about +Y
    const dot = fx * cx + fz * cz;
    const cross = fx * cz - fz * cx;       // y-component of (forward × toCam)
    let ang = Math.atan2(cross, dot);      // -π..π ; 0 = camera in front of ped
    const step = (Math.PI * 2) / this.atlas.yaws;
    let idx = Math.round(ang / step);
    idx = ((idx % this.atlas.yaws) + this.atlas.yaws) % this.atlas.yaws;
    return idx;
  }

  // list: [{ x, z, groundY, height, subject, facing }]  — subject = atlas subject index (ped type)
  update(list, camera) {
    const camX = camera.position.x, camZ = camera.position.z;
    const span = this.atlas.frame.span, foot = this.atlas.frame.foot;
    const count = Math.min(list.length, this.max);
    const off = this._uvOffset.array;
    for (let i = 0; i < count; i++) {
      const it = list[i];
      const h = it.height || 1.75;
      const cell = h * span;                       // square billboard, matches the baked cell
      // instanceMatrix carries translation (feet-minus-margin) + scale (width in x, height in y)
      this._p.set(it.x, (it.groundY || 0) - h * foot, it.z);
      this._q.identity();
      this._s.set(cell, cell, 1);
      this._m.compose(this._p, this._q, this._s);
      this.mesh.setMatrixAt(i, this._m);
      const yaw = this._yawIndex(it.x, it.z, it.facing || 0, camX, camZ);
      const [u, v] = this.atlas.cellUV(it.subject % this.atlas.n, yaw);
      off[i * 2] = u; off[i * 2 + 1] = v;
    }
    this.mesh.count = count;
    this.mesh.instanceMatrix.needsUpdate = true;
    this._uvOffset.needsUpdate = true;
  }

  setTint(hex) { this.material.uniforms.uTint.value.set(hex); }
  // No-op: exposure is now global (renderer.toneMappingExposure) — three's tone-mapping (canvas) and
  // the composer's OutputPass both read it, so impostors track day/night automatically. Kept so the
  // shell's citizens.setExposure(...) call site stays valid (Lane F may drop it — harmless either way).
  setExposure(_e) {}

  dispose() {
    this.mesh.geometry.dispose();
    this.material.dispose();
    this.atlas.dispose();
  }
}