index.ts

import * as path from 'path';

import type { Plugin } from 'rollup';

import type { RollupVirtualOptions } from '../types';

const PREFIX = `\0virtual:`;

export default function virtual(modules: RollupVirtualOptions): Plugin {
  const resolvedIds = new Map<string, string>();

  Object.keys(modules).forEach((id) => {
    resolvedIds.set(path.resolve(id), modules[id]);
  });

  return {
    name: 'virtual',

    resolveId(id, importer) {
      if (id in modules) return PREFIX + id;

      if (importer) {
        const importerNoPrefix = importer.startsWith(PREFIX)
          ? importer.slice(PREFIX.length)
          : importer;
        const resolved = path.resolve(path.dirname(importerNoPrefix), id);
        if (resolvedIds.has(resolved)) return PREFIX + resolved;
      }

      return null;
    },

    load(id) {
      if (id.startsWith(PREFIX)) {
        const idNoPrefix = id.slice(PREFIX.length);

        return idNoPrefix in modules ? modules[idNoPrefix] : resolvedIds.get(idNoPrefix);
      }

      return null;
    }
  };
}