@loaders.gl/core/src/lib/loader-utils/loader-context.ts

The core API for working with loaders.gl loaders and writers

// loaders.gl
// SPDX-License-Identifier: MIT
// Copyright (c) vis.gl contributors

import type {Loader, LoaderOptions, LoaderContext} from '@loaders.gl/loader-utils';
import {getFetchFunction} from './get-fetch-function';
import {extractQueryString, stripQueryString} from '../utils/url-utils';
import {path} from '@loaders.gl/loader-utils';

/** Properties for creating an updated context */
type LoaderContextProps = Omit<LoaderContext, 'fetch'> & Partial<Pick<LoaderContext, 'fetch'>>;

/**
 * "sub" loaders invoked by other loaders get a "context" injected on `this`
 * The context will inject core methods like `parse` and contain information
 * about loaders and options passed in to the top-level `parse` call.
 *
 * @param context
 * @param options
 * @param previousContext
 */
export function getLoaderContext(
  context: LoaderContextProps,
  options: LoaderOptions,
  parentContext: LoaderContext | null
): LoaderContext {
  // For recursive calls, we already have a context
  // TODO - add any additional loaders to context?
  if (parentContext) {
    return parentContext;
  }

  const newContext: LoaderContext = {
    fetch: getFetchFunction(options, context),
    ...context
  };

  // Parse URLs so that subloaders can easily generate correct strings
  if (newContext.url) {
    const baseUrl = stripQueryString(newContext.url);
    newContext.baseUrl = baseUrl;
    newContext.queryString = extractQueryString(newContext.url);
    newContext.filename = path.filename(baseUrl);
    newContext.baseUrl = path.dirname(baseUrl);
  }

  // Recursive loading does not use single loader
  if (!Array.isArray(newContext.loaders)) {
    newContext.loaders = null;
  }

  return newContext;
}

// eslint-disable-next-line complexity
export function getLoadersFromContext(
  loaders: Loader[] | Loader | undefined,
  context?: LoaderContext
): Loader | Loader[] | undefined {
  // A single loader (non-array) indicates no selection desired. Force select.
  if (loaders && !Array.isArray(loaders)) {
    return loaders;
  }

  // Create a merged list
  let candidateLoaders;
  if (loaders) {
    candidateLoaders = Array.isArray(loaders) ? loaders : [loaders];
  }
  if (context && context.loaders) {
    const contextLoaders = Array.isArray(context.loaders) ? context.loaders : [context.loaders];
    candidateLoaders = candidateLoaders ? [...candidateLoaders, ...contextLoaders] : contextLoaders;
  }
  // If no loaders, return null to look in globally registered loaders
  return candidateLoaders && candidateLoaders.length ? candidateLoaders : undefined;
}