// WebGPU rendering of the plate: a 2D color map or a lit 3D height field of
// the displacement (plus the stress-free shape), colored by the displacement
// or by the thickness. Both views paint the mount and the strike point on the
// surface as rings; the 3D view also stands a post at the mount, so that it
// stays visible when the ring is edge-on or lost on a steep bell, and stands a
// microphone where the listener is, framing the view to reach both.

import { type Grid, cellMask, insideCell } from "../params.ts";
import { lookAt, multiply, perspective } from "./mat4.ts";
import shaderCode from "./shaders.wgsl?raw";

export type ViewMode = "2d" | "3d";
export type ColorMode = "field" | "thickness";

export interface Marker {
  x: number;
  y: number;
  r: number;
}

/** Vertices of the mount post: 24 segments of two side triangles, plus a fan over each cap (see shaders.wgsl). */
const MOUNT_VERTS = 24 * 6 + 2 * 24 * 3;
/** Vertices of the microphone: a 16 by 24 surface of revolution, plus a fan closing its back (see shaders.wgsl). */
const MIC_VERTS = 16 * 24 * 6 + 16 * 3;
/** Its widest radius and the length of its body [m]: a large-diaphragm microphone, the same whatever the plate. */
const MIC_RADIUS = 0.028;
const MIC_ASPECT = 4.2;   // must match shaders.wgsl
const MIC_LENGTH = MIC_RADIUS * MIC_ASPECT;

/** Vertical field of view of the 3D view [rad], the framing margin around the scene, and the orbit limits. */
const FOV = 0.7;
const FIT_MARGIN = 1.1;
const DIST_MIN = 0.05;
const DIST_MAX = 200;

type Vec3 = [number, number, number];
const dot = (a: Vec3, b: Vec3) => a[0] * b[0] + a[1] * b[1] + a[2] * b[2];
const cross = (a: Vec3, b: Vec3): Vec3 => [a[1] * b[2] - a[2] * b[1], a[2] * b[0] - a[0] * b[2], a[0] * b[1] - a[1] * b[0]];
const unit = (a: Vec3): Vec3 => { const n = Math.hypot(a[0], a[1], a[2]) || 1; return [a[0] / n, a[1] / n, a[2] / n]; };

/**
 * The smallest orbit radius, about the plate's center along `dir`, at which
 * every one of `points` still falls inside the frustum, each point taken with
 * the radius it needs around it. The view is much wider than it is tall, so
 * fitting what is actually on screen rather than a bounding sphere makes a
 * large difference to how much of it the plate fills.
 */
function fitDistance(points: [Vec3, number][], dir: Vec3, aspect: number): number {
  const fwd: Vec3 = [-dir[0], -dir[1], -dir[2]];
  const right = unit(cross(fwd, [0, 1, 0]));
  const up = cross(right, fwd);
  const tanH = Math.tan(FOV / 2);
  let need = 0;
  for (const [p, r] of points) {
    const depth = dot(p, dir);
    const v = (Math.abs(dot(p, up)) + r) / tanH;
    const h = (Math.abs(dot(p, right)) + r) / (tanH * aspect);
    need = Math.max(need, depth + Math.max(v, h));
  }
  return Math.max(DIST_MIN, Math.min(DIST_MAX, need * FIT_MARGIN));
}

export class Renderer {
  mode: ViewMode = "2d";
  /** Vertical exaggeration of the 3D view. */
  exaggeration = 1;
  /** Color range |w| [m]; 0 means automatic (from the current maximum). */
  colorRange = 0;
  /** Show the total shape (initial shape plus deviation) rather than the deviation alone, in both views. */
  showShape = true;
  colorMode: ColorMode = "field";
  /** Orbit about the plate's center: yaw about the vertical, pitch above the plane of the plate. */
  camera = { yaw: 0.7, pitch: 0.5, dist: 0.95 };
  /**
   * Until the wheel is used, the orbit radius is chosen to frame the whole
   * scene, the microphone included. A listener a meter from a 16 inch cymbal
   * is drawn a meter from its center, so the cymbal is small in the view; that
   * is what a microphone a meter up really looks like. A double-click returns
   * to this framing, and to the opening angle, after moving the view.
   */
  private userZoomed = false;
  /** Markers drawn in both views; read at every render. */
  strike: Marker = { x: 0, y: 0, r: 0 };
  mount: Marker | null = null;
  /** Listener position in the plate's frame (z along the normal); the 3D view stands a microphone on that line. */
  listener: [number, number, number] | null = null;

  private device: GPUDevice;
  private canvas: HTMLCanvasElement;
  private ctx: GPUCanvasContext;
  private format: GPUTextureFormat;
  private uniform: GPUBuffer;
  private pipe2d: GPURenderPipeline;
  private pipe3d: GPURenderPipeline;
  private pipe3dMount: GPURenderPipeline;
  private pipe3dListener: GPURenderPipeline;
  private bgLayout: GPUBindGroupLayout;
  private index: GPUBuffer | null = null;
  private indexCount = 0;
  private depth: GPUTexture | null = null;
  private grid: Grid | null = null;
  private bindGroups = new Map<GPUBuffer, GPUBindGroup>();

  private w0: GPUBuffer | null = null;
  private w0Max = 0;
  private nw: GPUBuffer | null = null;
  private hn: GPUBuffer | null = null;
  private cm: GPUBuffer | null = null;
  private hRange: [number, number] = [0, 1];

  /** The grid of the field currently set, or null before setField. */
  get fieldGrid(): Grid | null {
    return this.grid;
  }

  /** The renderer draws nothing until setField gives it a grid. */
  constructor(device: GPUDevice, canvas: HTMLCanvasElement) {
    this.device = device;
    this.canvas = canvas;
    this.ctx = canvas.getContext("webgpu") as GPUCanvasContext;
    this.format = navigator.gpu.getPreferredCanvasFormat();
    this.ctx.configure({ device, format: this.format, alphaMode: "opaque" });
    this.uniform = device.createBuffer({ size: 176, usage: GPUBufferUsage.UNIFORM | GPUBufferUsage.COPY_DST });   // RU in shaders.wgsl: 44 f32
    const module = device.createShaderModule({ code: shaderCode });
    const vis = GPUShaderStage.VERTEX | GPUShaderStage.FRAGMENT;
    this.bgLayout = device.createBindGroupLayout({
      entries: [
        { binding: 0, visibility: vis, buffer: { type: "uniform" } },
        { binding: 1, visibility: vis, buffer: { type: "read-only-storage" } },
        { binding: 2, visibility: vis, buffer: { type: "read-only-storage" } },
        { binding: 3, visibility: vis, buffer: { type: "read-only-storage" } },
        { binding: 4, visibility: vis, buffer: { type: "read-only-storage" } },
        { binding: 5, visibility: vis, buffer: { type: "read-only-storage" } },
      ],
    });
    const layout = device.createPipelineLayout({ bindGroupLayouts: [this.bgLayout] });
    this.pipe2d = device.createRenderPipeline({
      layout,
      vertex: { module, entryPoint: "vs2d" },
      fragment: { module, entryPoint: "fs2d", targets: [{ format: this.format }] },
      primitive: { topology: "triangle-list" },
    });
    const depthStencil: GPUDepthStencilState = { format: "depth24plus", depthWriteEnabled: true, depthCompare: "less" };
    this.pipe3d = device.createRenderPipeline({
      layout,
      vertex: { module, entryPoint: "vs3d" },
      fragment: { module, entryPoint: "fs3d", targets: [{ format: this.format }] },
      primitive: { topology: "triangle-list", cullMode: "none" },
      depthStencil,
    });
    this.pipe3dMount = device.createRenderPipeline({
      layout,
      vertex: { module, entryPoint: "vs3dMount" },
      fragment: { module, entryPoint: "fs3dMount", targets: [{ format: this.format }] },
      primitive: { topology: "triangle-list", cullMode: "none" },
      depthStencil,
    });
    this.pipe3dListener = device.createRenderPipeline({
      layout,
      vertex: { module, entryPoint: "vs3dListener" },
      fragment: { module, entryPoint: "fs3dListener", targets: [{ format: this.format }] },
      primitive: { topology: "triangle-list", cullMode: "none" },
      depthStencil,
    });
    this.installControls();
  }

  /**
   * Sets the grid and the per-node buffers the views read: the stress-free
   * shape (added to the displayed field when showShape is on; w0Max is its
   * largest magnitude, for the automatic color range), the node weights (zero
   * outside the plate), and the thickness with its range for the thickness
   * coloring. Called at every Start and for the preview of the design; the
   * camera and the canvas controls persist.
   */
  setField(grid: Grid, w0: GPUBuffer, nw: GPUBuffer, hn: GPUBuffer, w0Max: number, hRange: [number, number]): void {
    this.grid = grid;
    this.w0 = w0;
    this.w0Max = w0Max;
    this.nw = nw;
    this.hn = hn;
    this.hRange = hRange;
    this.bindGroups.clear();
    const cmData = cellMask(grid);
    this.cm?.destroy();
    this.cm = this.device.createBuffer({ size: Math.max(16, cmData.byteLength), usage: GPUBufferUsage.STORAGE | GPUBufferUsage.COPY_DST });
    this.device.queue.writeBuffer(this.cm, 0, cmData);
    // Triangle indices of the height field (cells of the plate only).
    const { nx, ny } = grid;
    const idx = new Uint32Array((nx - 1) * (ny - 1) * 6);
    let k = 0;
    for (let j = 0; j < ny - 1; j++) {
      for (let i = 0; i < nx - 1; i++) {
        if (!insideCell(grid, i, j)) continue;
        const a = j * nx + i, b = a + 1, c = a + nx, d = c + 1;
        idx[k++] = a; idx[k++] = b; idx[k++] = d;
        idx[k++] = a; idx[k++] = d; idx[k++] = c;
      }
    }
    this.indexCount = k;
    this.index?.destroy();
    this.index = this.device.createBuffer({ size: Math.max(16, idx.byteLength), usage: GPUBufferUsage.INDEX | GPUBufferUsage.COPY_DST });
    this.device.queue.writeBuffer(this.index, 0, idx);
  }

  private installControls(): void {
    let dragging = false, lastX = 0, lastY = 0;
    this.canvas.addEventListener("pointerdown", (e) => {
      dragging = true; lastX = e.clientX; lastY = e.clientY;
      this.canvas.setPointerCapture(e.pointerId);
    });
    this.canvas.addEventListener("pointerup", () => (dragging = false));
    this.canvas.addEventListener("pointermove", (e) => {
      if (!dragging || this.mode !== "3d") return;
      this.camera.yaw += (e.clientX - lastX) * 0.01;
      this.camera.pitch = Math.max(-1.5, Math.min(1.5, this.camera.pitch + (e.clientY - lastY) * 0.01));
      lastX = e.clientX; lastY = e.clientY;
    });
    this.canvas.addEventListener("wheel", (e) => {
      if (this.mode !== "3d") return;
      e.preventDefault();
      this.userZoomed = true;
      this.camera.dist = Math.max(DIST_MIN, Math.min(DIST_MAX, this.camera.dist * Math.exp(e.deltaY * 0.001)));
    }, { passive: false });
    this.canvas.addEventListener("dblclick", () => {
      this.camera.yaw = 0.7;
      this.camera.pitch = 0.5;
      this.userZoomed = false;
    });
  }

  /**
   * The points the 3D framing has to hold: the corners of the box around the
   * plate at its displayed height, and the two ends of the microphone, each
   * with the radius it needs around it.
   */
  private fitPoints(L: [number, number, number] | null, Ln: number, zmax: number): [Vec3, number][] {
    const g = this.grid!;
    const hx = 0.5 * (g.nx - 1) * g.hx, hy = 0.5 * (g.ny - 1) * g.hy, hz = Math.max(zmax * this.exaggeration, 1e-4);
    // The plate's frame in the world (see `world` in shaders.wgsl): x, height, -y.
    const pts: [Vec3, number][] = [];
    for (const sx of [-1, 1]) for (const sy of [-1, 1]) for (const sz of [-1, 1]) pts.push([[sx * hx, sz * hz, -sy * hy], 0]);
    if (L && Ln > 0) {
      for (const d of [Ln, Ln + MIC_LENGTH]) {
        const s = d / Ln;
        pts.push([[L[0] * s, L[2] * s, -L[1] * s], MIC_RADIUS]);
      }
    }
    return pts;
  }

  private resize(): void {
    const dpr = window.devicePixelRatio || 1;
    const w = Math.max(1, Math.floor(this.canvas.clientWidth * dpr));
    const h = Math.max(1, Math.floor(this.canvas.clientHeight * dpr));
    if (this.canvas.width !== w || this.canvas.height !== h || !this.depth) {
      this.canvas.width = w;
      this.canvas.height = h;
      this.depth?.destroy();
      this.depth = this.device.createTexture({ size: [w, h], format: "depth24plus", usage: GPUTextureUsage.RENDER_ATTACHMENT });
    }
  }

  /** Renders the w field held in `wBuffer` (f32 per node). `wmax`, the largest |w|, drives the automatic color range. */
  render(encoder: GPUCommandEncoder, wBuffer: GPUBuffer, wmax: number): void {
    if (!this.grid || !this.w0 || !this.nw || !this.hn || !this.cm || !this.index) return;
    this.resize();
    const aspect = this.canvas.width / this.canvas.height;
    const auto = wmax + (this.showShape ? this.w0Max : 0);
    const range = this.colorRange > 0 ? this.colorRange : Math.max(auto, 1e-6);
    const u = new Float32Array(44);
    const ui = new Uint32Array(u.buffer);
    // The microphone stands where the listener is, at the listener distance from the center of the plate,
    // so the framing has to reach out to it as well as around the plate.
    const L = this.listener;
    const Ln = L ? Math.hypot(L[0], L[1], L[2]) : 0;
    const drawListener = !!L && Ln > 0;
    const dir: Vec3 = [
      Math.cos(this.camera.pitch) * Math.sin(this.camera.yaw),
      Math.sin(this.camera.pitch),
      Math.cos(this.camera.pitch) * Math.cos(this.camera.yaw),
    ];
    const sceneRadius = this.fitPoints(drawListener && this.mode === "3d" ? L : null, Ln, auto);
    if (!this.userZoomed && this.mode === "3d") this.camera.dist = fitDistance(sceneRadius, dir, aspect);
    const eye: Vec3 = [this.camera.dist * dir[0], this.camera.dist * dir[1], this.camera.dist * dir[2]];
    const reach = Math.max(...sceneRadius.map(([p]) => Math.hypot(p[0], p[1], p[2])));
    const near = 0.02 * this.camera.dist, far = 4 * this.camera.dist + 4 * reach;
    const mvp = multiply(perspective(FOV, aspect, near, far), lookAt(eye, [0, 0, 0], [0, 1, 0]));
    u.set(mvp, 0);
    ui[16] = this.grid.nx; ui[17] = this.grid.ny;
    u[18] = this.grid.hx; u[19] = this.grid.hy;
    u[20] = this.exaggeration; u[21] = range; u[22] = aspect;
    ui[23] = this.mode === "3d" ? 1 : 0;
    u[24] = this.strike.x; u[25] = this.strike.y; u[26] = this.strike.r;
    u[27] = this.mount?.x ?? 0; u[28] = this.mount?.y ?? 0; u[29] = this.mount?.r ?? 0;
    u[30] = 0.35; u[31] = 0.85; u[32] = 0.4;   // light, from above and to one side
    ui[33] = this.showShape ? 1 : 0;
    ui[34] = this.colorMode === "thickness" ? 1 : 0;
    ui[35] = this.mount ? 1 : 0;
    u[36] = this.hRange[0]; u[37] = this.hRange[1];
    if (drawListener) { u[38] = L![0] / Ln; u[39] = L![1] / Ln; u[40] = L![2] / Ln; }
    u[41] = Ln;
    u[42] = MIC_RADIUS;
    ui[43] = drawListener ? 1 : 0;
    this.device.queue.writeBuffer(this.uniform, 0, u);

    let bg = this.bindGroups.get(wBuffer);
    if (!bg) {
      bg = this.device.createBindGroup({
        layout: this.bgLayout,
        entries: [
          { binding: 0, resource: { buffer: this.uniform } },
          { binding: 1, resource: { buffer: wBuffer } },
          { binding: 2, resource: { buffer: this.w0 } },
          { binding: 3, resource: { buffer: this.nw } },
          { binding: 4, resource: { buffer: this.hn } },
          { binding: 5, resource: { buffer: this.cm } },
        ],
      });
      this.bindGroups.set(wBuffer, bg);
    }
    const view = this.ctx.getCurrentTexture().createView();
    const clear = { r: 0.11, g: 0.12, b: 0.14, a: 1 };
    if (this.mode === "2d") {
      const pass = encoder.beginRenderPass({ colorAttachments: [{ view, clearValue: clear, loadOp: "clear", storeOp: "store" }] });
      pass.setPipeline(this.pipe2d);
      pass.setBindGroup(0, bg);
      pass.draw(3);
      pass.end();
    } else {
      const pass = encoder.beginRenderPass({
        colorAttachments: [{ view, clearValue: clear, loadOp: "clear", storeOp: "store" }],
        depthStencilAttachment: { view: this.depth!.createView(), depthClearValue: 1, depthLoadOp: "clear", depthStoreOp: "store" },
      });
      pass.setPipeline(this.pipe3d);
      pass.setBindGroup(0, bg);
      pass.setIndexBuffer(this.index, "uint32");
      pass.drawIndexed(this.indexCount);
      if (this.mount) {
        // The post at the mount; the ring on the surface is painted by fs3d.
        pass.setPipeline(this.pipe3dMount);
        pass.setBindGroup(0, bg);
        pass.draw(MOUNT_VERTS);
      }
      if (drawListener) {
        pass.setPipeline(this.pipe3dListener);
        pass.setBindGroup(0, bg);
        pass.draw(MIC_VERTS);
      }
      pass.end();
    }
  }
}