type RowFormat = "f32" | "u32" | "i32";
type RowDescriptor = {
  name: string;
  rows: number;
  stride: number;
  format: RowFormat;
};

const views = {
  f32: Float32Array,
  u32: Uint32Array,
  i32: Int32Array,
};

export class SharedRows {
  readonly name: string;
  rows: number;
  readonly stride: number;
  readonly format: RowFormat;
  buffer: SharedArrayBuffer;

  constructor({ name, rows, stride, format }: RowDescriptor) {
    this.name = name;
    this.rows = rows;
    this.stride = stride;
    this.format = format;
    this.buffer = new SharedArrayBuffer(rows * stride);
  }

  resize(rows: number) {
    if (rows <= this.rows) return this;
    const previous = this.view;
    this.rows = rows;
    this.buffer = new SharedArrayBuffer(rows * this.stride);
    this.view.set(previous);
    return this;
  }

  get view() {
    const View = views[this.format];
    return new View(this.buffer);
  }

  row(index: number) {
    if (!Number.isInteger(index) || index < 0 || index >= this.rows)
      throw new RangeError(`ROW_RANGE: ${this.name}[${index}]`);
    const width = this.stride / views[this.format].BYTES_PER_ELEMENT;
    return this.view.subarray(index * width, (index + 1) * width);
  }

  write(index: number, values: ArrayLike<number>) {
    const row = this.row(index);
    if (values.length !== row.length) throw new RangeError("ROW_WIDTH");
    row.set(values);
    return this;
  }
}

function deserialize(serialized: string) {
  let offset = 0;
  const skip = () => {
    while (/\s/u.test(serialized[offset] ?? "")) offset++;
  };
  const take = (character: string) => {
    skip();
    if (serialized[offset] !== character)
      throw new SyntaxError(`Expected ${character} at ${offset}`);
    offset++;
  };
  const word = () => {
    skip();
    const start = offset;
    while (offset < serialized.length && !/[\s()]/u.test(serialized[offset]))
      offset++;
    return serialized.slice(start, offset);
  };
  const value = (): any => {
    skip();
    if (serialized[offset] === '"') {
      const start = offset++;
      while (offset < serialized.length) {
        if (serialized[offset] === "\\") offset += 2;
        else if (serialized[offset++] === '"') break;
      }
      return JSON.parse(serialized.slice(start, offset));
    }
    if (serialized[offset] !== "(") {
      const token = word();
      if (token === "true") return true;
      if (token === "false") return false;
      if (token === "null") return null;
      const number = Number(token);
      if (!Number.isNaN(number)) return number;
      throw new SyntaxError(`Unknown value ${token}`);
    }
    take("(");
    const tag = word();
    if (tag === "array") {
      const result = [];
      skip();
      while (serialized[offset] !== ")") result.push(value());
      take(")");
      return result;
    }
    if (tag === "object") {
      const result: Record<string, unknown> = {};
      skip();
      while (serialized[offset] !== ")") {
        take("(");
        if (word() !== "field") throw new SyntaxError("Expected field");
        const key = value();
        result[key] = value();
        take(")");
        skip();
      }
      take(")");
      return result;
    }
    if (tag === "yawn-graph") {
      if (word() !== "1") throw new SyntaxError("Graph version");
      const result = value();
      take(")");
      return result;
    }
    throw new SyntaxError(`Unknown list ${tag}`);
  };
  return value();
}

export class YawnCore {
  readonly ready = Promise.resolve();
  readonly features = new Set(["timestamp-query", "indirect-first-instance"]);
  readonly graphs: any[] = [];
  readonly serializedGraphs: string[] = [];
  readonly loadouts: string[] = [];
  readonly uploadedTextures: { name: string; mipLevel: number }[] = [];
  fps?: number;
  disposed = false;
  #arrays = new Map<string, SharedRows>();
  #nextObjects = new Map<string, number>();

  constructor() {
    this.#arrays.set(
      "signals",
      new SharedRows({ name: "signals", rows: 1, stride: 32, format: "f32" }),
    );
  }

  createRows(descriptor: RowDescriptor) {
    const current = this.#arrays.get(descriptor.name);
    if (current) {
      if (
        current.stride !== descriptor.stride ||
        current.format !== descriptor.format
      )
        throw new Error(`ROW_LAYOUT: ${descriptor.name}`);
      return Promise.resolve(current.resize(descriptor.rows));
    }
    const rows = new SharedRows(descriptor);
    this.#arrays.set(descriptor.name, rows);
    return Promise.resolve(rows);
  }

  createRowsBatch(descriptors: RowDescriptor[]) {
    return Promise.all(
      descriptors.map((descriptor) => this.createRows(descriptor)),
    );
  }

  deleteRows(name: string) {
    this.#arrays.delete(name);
    return Promise.resolve();
  }

  allocateObject(name: string, count = 1) {
    const id = this.#nextObjects.get(name) ?? 0;
    this.#nextObjects.set(name, id + count);
    const rows = this.array(name);
    rows.resize(id + count);
    return Promise.resolve(id);
  }

  deleteObject() {
    return Promise.resolve();
  }

  array(name: string) {
    const rows = this.#arrays.get(name);
    if (!rows) throw new Error(`UNKNOWN_ARRAY: ${name}`);
    return rows;
  }

  compileGraph(serialized: string) {
    this.serializedGraphs.push(serialized);
    this.graphs.push(deserialize(serialized));
    return Promise.resolve(`loadout-${this.graphs.length}`);
  }

  switchLoadout(id: string) {
    this.loadouts.push(id);
    return Promise.resolve();
  }

  setFps(fps: number) {
    this.fps = fps;
    return Promise.resolve();
  }

  uploadTexture(name: string, _image: unknown, mipLevel = 0) {
    this.uploadedTextures.push({ name, mipLevel });
    return Promise.resolve();
  }

  deleteTexture() {
    return Promise.resolve();
  }

  dispose() {
    this.disposed = true;
  }
}