silphius/app/ecs/schema.js

const encoder = new TextEncoder();

export default class Schema {

  $$size = 0;

  specification;

  static viewGetMethods = {
    uint8: 'getUint8',
    int8: 'getInt8',
    uint16: 'getUint16',
    int16: 'getInt16',
    uint32: 'getUint32',
    int32: 'getInt32',
    float32: 'getFloat32',
    float64: 'getFloat64',
    int64: 'getBigInt64',
    uint64: 'getBigUint64',
  };

  static viewSetMethods = {
    uint8: 'setUint8',
    int8: 'setInt8',
    uint16: 'setUint16',
    int16: 'setInt16',
    uint32: 'setUint32',
    int32: 'setInt32',
    float32: 'setFloat32',
    float64: 'setFloat64',
    int64: 'setBigInt64',
    uint64: 'setBigUint64',
  };

  constructor(specification) {
    this.specification = this.constructor.normalize(specification);
    // Try to calculate static size.
    for (const i in this.specification) {
      const {type} = this.specification[i];
      const size = this.constructor.sizeOfType(type);
      if (0 === size) {
        this.$$size = 0;
        break;
      }
      this.$$size += size;
    }
  }

  [Symbol.iterator]() {
    return Object.entries(this.specification).values();
  }

  static defaultValueForType(type) {
    switch (type) {
      case 'uint8': case 'int8':
      case 'uint16': case 'int16':
      case 'uint32': case 'int32':
      case 'uint64': case 'int64':
      case 'float32': case 'float64': {
        return 0;
      }
      case 'string': {
        return '';
      }
    }
  }

  has(key) {
    return key in this.specification;
  }

  static normalize(specification) {
    const normalized = Object.create(null);
    for (const i in specification) {
      normalized[i] = 'string' === typeof specification[i]
        ? {type: specification[i]}
        : specification[i];
      if (!this.validateType(normalized[i].type)) {
        throw new TypeError(`unknown schema type: ${normalized[i].type}`);
      }
      normalized[i].defaultValue = normalized[i].defaultValue || this.defaultValueForType(normalized[i].type);
    }
    return normalized;
  }

  readSize(view, cursor) {
    let fullSize = 0;
    for (const i in this.specification) {
      const {type} = this.specification[i];
      const size = this.constructor.sizeOfType(type);
      if (0 === size) {
        switch (type) {
          case 'string': {
            const length = view.getUint32(cursor, true);
            cursor += 4 + length;
            fullSize += 4;
            fullSize += length;
            break;
          }
        }
      }
      else {
        cursor += size;
        fullSize += size;
      }
    }
    return fullSize;
  }

  get size() {
    return this.$$size;
  }

  sizeOf(concrete) {
    let fullSize = 0;
    for (const i in this.specification) {
      const {type} = this.specification[i];
      const size = this.constructor.sizeOfType(type);
      if (0 === size) {
        switch (type) {
          case 'string':
            fullSize += 4;
            fullSize += (encoder.encode(concrete[i])).length;
            break;
        }
      }
      else {
        fullSize += size;
      }
    }
    return fullSize;
  }

  static sizeOfType(type) {
    switch (type) {
      case 'uint8': case 'int8': {
        return 1;
      }
      case 'uint16': case 'int16': {
        return 2;
      }
      case 'uint32': case 'int32': case 'float32': {
        return 4;
      }
      case 'uint64': case 'int64': case 'float64': {
        return 8;
      }
      default: return 0;
    }
  }

  static validateType(type) {
    return [
      'uint8', 'int8',
      'uint16', 'int16',
      'uint32', 'int32',
      'uint64', 'int64',
      'float32', 'float64',
      'string',
    ]
      .includes(type);
  }

}