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);
  }

  static deserialize(view, offset, specification) {
    const viewGetMethod = this.viewGetMethods[specification.type];
    if (viewGetMethod) {
      const value = view[viewGetMethod](offset.value, true);
      offset.value += this.size(specification);
      return value;
    }
    switch (specification.type) {
      case 'array': {
        const length = view.getUint32(offset.value, true);
        offset.value += 4;
        const value = [];
        for (let i = 0; i < length; ++i) {
          value.push(this.deserialize(view, offset, specification.subtype));
        }
        return value;
      }
      case 'object': {
        const value = {};
        for (const key in specification.properties) {
          value[key] = this.deserialize(view, offset, specification.properties[key]);
        }
        return value;
      }
      case 'string': {
        const length = view.getUint32(offset.value, true);
        offset.value += 4;
        const {buffer, byteOffset} = view;
        const decoder = new TextDecoder();
        const value = decoder.decode(new DataView(buffer, byteOffset + offset.value, length));
        offset.value += length;
        return value;
      }
    }
  }

  deserialize(view, offset = 0) {
    const wrapped = {value: offset};
    return this.constructor.deserialize(view, wrapped, this.specification);
  }

  static defaultValue(specification) {
    if (specification.defaultValue) {
      return specification.defaultValue;
    }
    switch (specification.type) {
      case 'uint8': case 'int8':
      case 'uint16': case 'int16':
      case 'uint32': case 'int32':
      case 'uint64': case 'int64':
      case 'float32': case 'float64': {
        return 0;
      }
      case 'array': {
        return [];
      }
      case 'object': {
        const object = {};
        for (const key in specification.properties) {
          object[key] = this.defaultValue(specification.properties[key]);
        }
        return object;
      }
      case 'string': {
        return '';
      }
    }
  }

  defaultValue() {
    return this.constructor.defaultValue(this.specification);
  }

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

  static normalize(specification) {
    let normalized = specification;
    switch (specification.type) {
      case 'array': {
        normalized.subtype = this.normalize(specification.subtype);
        break;
      }
      case 'object': {
        for (const key in specification.properties) {
          normalized.properties[key] = this.normalize(specification.properties[key])
        }
        break;
      }
      case 'uint8':
      case 'int8':
      case 'uint16':
      case 'int16':
      case 'uint32':
      case 'int32':
      case 'uint64':
      case 'int64':
      case 'float32':
      case 'float64':
      case 'string': {
        break;
      }
      default:
        throw new TypeError(`invalid specification: ${JSON.stringify(specification)}`);
    }
    return {...normalized, defaultValue: this.defaultValue(normalized)};
  }

  static readSize(view, offset, specification) {
    const size = this.size(specification);
    if (size > 0) {
      return size;
    }
    switch (specification.type) {
      case 'array': {
        const length = view.getUint32(offset.value, true);
        offset.value += 4;
        let arraySize = 0;
        for (let i = 0; i < length; ++i) {
          arraySize += this.readSize(view, offset, specification.subtype);
        }
        return 4 + arraySize;
      }
      case 'object': {
        let objectSize = 0;
        for (const key in specification.properties) {
          objectSize += this.readSize(view, offset, specification.properties[key]);
        }
        return objectSize;
      }
      case 'string': {
        const length = view.getUint32(offset.value, true);
        offset.value += 4 + length;
        return 4 + length;
      }
    }
  }

  readSize(view, offset) {
    const wrapped = {value: offset};
    return this.constructor.readSize(view, wrapped, this.specification);
  }

  static serialize(source, view, offset, specification) {
    const viewSetMethod = this.viewSetMethods[specification.type];
    if (viewSetMethod) {
      view[viewSetMethod](offset, source, true);
      return this.size(specification);
    }
    switch (specification.type) {
      case 'array': {
        view.setUint32(offset, source.length, true);
        offset += 4;
        let arraySize = 0;
        for (const element of source) {
          arraySize += this.serialize(
            element,
            view,
            offset + arraySize,
            specification.subtype,
          );
        }
        return 4 + arraySize;
      }
      case 'object': {
        let objectSize = 0;
        for (const key in specification.properties) {
          objectSize += this.serialize(
            source[key],
            view,
            offset + objectSize,
            specification.properties[key],
          );
        }
        return objectSize;
      }
      case 'string': {
        const encoder = new TextEncoder();
        const bytes = encoder.encode(source);
        view.setUint32(offset, bytes.length, true);
        offset += 4;
        for (let i = 0; i < bytes.length; ++i) {
          view.setUint8(offset++, bytes[i]);
        }
        return 4 + bytes.length;
      }
    }
  }

  serialize(source, view, offset = 0) {
    this.constructor.serialize(source, view, offset, this.specification);
  }

  static sizeOf(concrete, specification) {
    const size = this.size(specification);
    if (size > 0) {
      return size;
    }
    let fullSize = 0;
    const {type} = specification;
    switch (type) {
      case 'array': {
        fullSize += 4;
        for (const element of concrete) {
          fullSize += this.sizeOf(element, specification.subtype);
        }
        break;
      }
      case 'object': {
        for (const key in specification.properties) {
          fullSize += this.sizeOf(concrete[key], specification.properties[key]);
        }
        break;
      }
      case 'string':
        fullSize += 4;
        fullSize += (encoder.encode(concrete)).length;
        break;
    }
    return fullSize;
  }

  sizeOf(concrete) {
    return this.constructor.sizeOf(concrete, this.specification);
  }

  static size(specification) {
    switch (specification.type) {
      case 'array': return 0;
      case 'object': {
        let size = 0;
        for (const key in specification.properties) {
          const propertySize = this.size(specification.properties[key]);
          if (0 === propertySize) {
            return 0;
          }
          size += propertySize;
        }
        return size;
      }
      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;
    }
  }

  size() {
    return this.constructor.size(this.specification);
  }

}