@loaders.gl/json/src/lib/encoder-utils/encode-table-row.ts

Framework-independent loader for JSON and streaming JSON formats

// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors
// Copyright 2022 Foursquare Labs, Inc.

import {Feature, Table, getTableRowAsObject} from '@loaders.gl/schema';
import {getRowPropertyObject} from './encode-utils';
import {Utf8ArrayBufferEncoder} from './utf8-encoder';

type Row = {[key: string]: unknown};

// Helpers

/**
 * Encode a row. Currently this ignores properties in the geometry column.
 */
export function encodeTableRow(
  table: Table,
  rowIndex: number,
  geometryColumnIndex: number,
  utf8Encoder: Utf8ArrayBufferEncoder
): void {
  const row = getTableRowAsObject(table, rowIndex);
  if (!row) return;
  const featureWithProperties = getFeatureFromRow(table, row, geometryColumnIndex);
  const featureString = JSON.stringify(featureWithProperties);
  utf8Encoder.push(featureString);
}

/**
 * Encode a row as a Feature. Currently this ignores properties objects in the geometry column.
 */
function getFeatureFromRow(table: Table, row: Row, geometryColumnIndex: number): Feature {
  // Extract non-feature/geometry properties
  const properties = getRowPropertyObject(table, row, [geometryColumnIndex]);

  // Extract geometry feature
  const columnName = table.schema?.fields[geometryColumnIndex].name;
  let featureOrGeometry =
    columnName && (row[columnName] as {[key: string]: unknown} | string | null | undefined);

  // GeoJSON support null geometries
  if (!featureOrGeometry) {
    // @ts-ignore Feature type does not support null geometries
    return {type: 'Feature', geometry: null, properties};
  }

  // Support string geometries?
  // TODO: This assumes GeoJSON strings, which may not be the correct format
  // (could be WKT, encoded WKB...)
  if (typeof featureOrGeometry === 'string') {
    try {
      featureOrGeometry = JSON.parse(featureOrGeometry);
    } catch (err) {
      throw new Error('Invalid string geometry');
    }
  }

  if (typeof featureOrGeometry !== 'object' || typeof featureOrGeometry?.type !== 'string') {
    throw new Error('invalid geometry column value');
  }

  if (featureOrGeometry?.type === 'Feature') {
    // @ts-ignore Feature type does not support null geometries
    return {...featureOrGeometry, properties};
  }

  // @ts-ignore Feature type does not support null geometries
  return {type: 'Feature', geometry: featureOrGeometry, properties};
}