replace-module.mjs

import fs from "node:fs/promises";

const DEFAULT_ON_RESOLVE_CONCEPTS = { filter: /./, namespace: "file" };
const DEFAULT_ON_LOAD_CONCEPTS = {
  filter: /\.(?:js|json|mjs|cjs)$/,
  namespace: "file",
};

function processReplacements(replacements) {
  const onResolveReplacements = new Map();
  const onLoadReplacements = new Map();
  const onLoadProcessors = new Map();

  const checkPathReplaced = (module) => {
    if (!onResolveReplacements.has(module)) {
      return;
    }

    throw new Error(`module: '${module}' already replaced with another path.`);
  };

  const checkTextReplaced = (module) => {
    if (!onLoadReplacements.has(module)) {
      return;
    }

    throw new Error(
      `module: '${module}' already replaced with another content.`
    );
  };

  for (const replacement of replacements) {
    const { module } = replacement;

    if (typeof module !== "string") {
      throw new TypeError("'module' option is required.");
    }

    if (
      Reflect.has(replacement, "external") ||
      Reflect.has(replacement, "path")
    ) {
      if (module === "*") {
        throw new Error("Can not replace all modules with the same path.");
      }

      checkPathReplaced(module);

      onResolveReplacements.set(
        module,
        Reflect.has(replacement, "external")
          ? { external: true, path: replacement.external }
          : { path: replacement.path }
      );

      continue;
    }

    if (Reflect.has(replacement, "text")) {
      if (module === "*") {
        throw new Error("Can not replace all modules with the same content.");
      }

      checkPathReplaced(module);
      checkTextReplaced(module);

      onLoadReplacements.set(module, {
        contents: replacement.text,
        loader: replacement.loader,
      });

      continue;
    }

    checkPathReplaced(module);
    checkTextReplaced(module);

    if (!onLoadProcessors.has(module)) {
      onLoadProcessors.set(module, []);
    }

    const processFunctions = onLoadProcessors.get(module);

    if (Reflect.has(replacement, "process")) {
      const { process } = replacement;
      if (typeof process !== "function") {
        throw new TypeError("'process' option should be a function.");
      }

      processFunctions.push(process);
      continue;
    }

    if (
      Reflect.has(replacement, "find") &&
      Reflect.has(replacement, "replacement")
    ) {
      processFunctions.push((text) =>
        text.replaceAll(replacement.find, replacement.replacement)
      );
      continue;
    }

    console.log(replacement);
    throw new Error("Unexpected replacement option.");
  }

  return { onResolveReplacements, onLoadReplacements, onLoadProcessors };
}

function setupOnResolveListener(build, { concepts, replacements }) {
  if (replacements.size === 0) {
    return;
  }

  // `build.resolve()` will call `onResolve` listener
  // Use a `Set` to avoid infinite loop
  const seenModules = new Set();
  build.onResolve(concepts, async (args) => {
    if (!(args.kind === "require-call" || args.kind === "import-statement")) {
      return;
    }

    const key = JSON.stringify(args);
    if (seenModules.has(key)) {
      return;
    }
    seenModules.add(key);

    const resolveResult = await build.resolve(args.path, {
      importer: args.importer,
      namespace: args.namespace,
      resolveDir: args.resolveDir,
      kind: args.kind,
      pluginData: args.pluginData,
    });

    // `build.resolve()` seems not respecting `browser` field in `package.json`,
    // `resolveResult` maybe not correct, return `undefined` to let esbuild process the file.
    return replacements.get(resolveResult.path);
  });
}

function setupOnLoadListener(build, { concepts, replacements, processors }) {
  if (replacements.size === 0 && processors.size === 0) {
    return;
  }

  const processFunctionsForAllModules = processors.has("*")
    ? processors.get("*")
    : [];

  build.onLoad(concepts, async ({ path: file }) => {
    if (replacements.has(file)) {
      return replacements.get(file);
    }

    const processFunctions = [
      ...processFunctionsForAllModules,
      ...(processors.has(file) ? processors.get(file) : []),
    ];

    if (processFunctions.length === 0) {
      return;
    }

    const original = await fs.readFile(file, "utf8");

    let text = original;
    for (const process of processFunctions) {
      text = process(text);
    }

    // For files not JavaScript, we need add correct `loader` to the result,
    // We can simply return `undefined` to let esbuild process the file.
    if (original === text) {
      return;
    }

    return { contents: text };
  });
}

export default function esbuildPluginReplaceModule({
  onLoadConcepts = DEFAULT_ON_LOAD_CONCEPTS,
  onResolveConcepts = DEFAULT_ON_RESOLVE_CONCEPTS,
  replacements,
}) {
  const { onResolveReplacements, onLoadReplacements, onLoadProcessors } =
    processReplacements(replacements);
  const onResolveListenerOptions = {
    concepts: onResolveConcepts,
    replacements: onResolveReplacements,
  };
  const onLoadListenerOptions = {
    concepts: onLoadConcepts,
    replacements: onLoadReplacements,
    processors: onLoadProcessors,
  };

  return {
    name: "replace-module",
    setup(build) {
      setupOnResolveListener(build, onResolveListenerOptions);
      setupOnLoadListener(build, onLoadListenerOptions);
    },
  };
}