index.js

const camelcase = require("camelcase");
const MagicString = require("magic-string");
const {walk} = require("estree-walker");
const isReference = require("is-reference");
const {attachScopes} = require("@rollup/pluginutils");

function analyzeImport(node, importBindings, code) {
  code.remove(node.start, node.end);
  for (const spec of node.specifiers) {
    importBindings.set(spec.local.name, [
      spec.imported ? spec.imported.name : "default",
      node.source.value
    ]);
  }
}

function analyzeExportDefault(node, exportBindings, code) {
  if (node.declaration.type === "Identifier") {
    exportBindings.set("default", node.declaration.name);
    code.remove(node.start, node.end);
  } else if (
    node.declaration.id && (
      node.declaration.type === "ClassDeclaration" ||
      node.declaration.type === "FunctionDeclaration"
    )
  ) {
    exportBindings.set("default", node.declaration.id.name);
    code.remove(node.start, node.declaration.start);
  } else {
    exportBindings.set("default", "_iife_default");
    code.overwrite(node.start, node.declaration.start, "var _iife_default = ", {
      contentOnly: true
    });
  }
}

function analyzeExportNamed(node, exportBindings, code) {
  if (!node.declaration) {
    for (const spec of node.specifiers) {
      exportBindings.set(
        spec.exported.name, node.source ?
        [spec.local.name, node.source.value] : spec.local.name
      );
    }
    code.remove(node.start, node.end);
  } else {
    if (node.declaration.type === "VariableDeclaration") {
      for (const dec of node.declaration.declarations) {
        exportBindings.set(dec.id.name, dec.id.name);
      }
    } else {
      exportBindings.set(node.declaration.id.name, node.declaration.id.name);
    }
    code.remove(node.start, node.declaration.start);
  }
}

function transform({
  code,
  parse,
  ast = parse(code),
  sourcemap = false,
  strict = false,
  resolveGlobal = () => {},
  name
}) {
  code = new MagicString(code);
  resolveGlobal = createResolveGlobal(resolveGlobal);

  const importBindings = new Map; // name -> [property, source]
  const exportBindings = new Map;
  let scope = attachScopes(ast, "scope");

  for (const node of ast.body) {
    if (node.type === "ImportDeclaration") {
      analyzeImport(node, importBindings, code);
    } else if (node.type === "ExportDefaultDeclaration") {
      analyzeExportDefault(node, exportBindings, code);
    } else if (node.type === "ExportNamedDeclaration") {
      analyzeExportNamed(node, exportBindings, code);
    }
  }

  const globals = new Set;

  for (const [, source] of importBindings.values()) {
    globals.add(resolveGlobal(source));
  }

  walk(ast, {
    enter(node, parent) {
      if (/^(import|export)/i.test(node.type)) {
        this.skip();
      }
      if (node.scope) {
        scope = node.scope;
      }
      if (isReference(node, parent)) {
        if (importBindings.has(node.name) && !scope.contains(node.name)) {
          overwriteVar(node, parent, getBindingName(importBindings.get(node.name)));
        } else if (globals.has(node.name) && scope.contains(node.name)) {
          overwriteVar(node, parent, `_local_${node.name}`);
        }
      }
    },
    leave(node) {
      if (node.scope) {
        scope = node.scope.parent;
      }
    }
  });

  code.appendLeft(
    ast.body[0].start,
    `${getPrefix()}(function () {\n${strict ? "'use strict';\n" : ""}`
  );
  code.appendRight(
    ast.body[ast.body.length - 1].end,
    `\n${getReturn()}})();`
  );

  return {
    code: code.toString(),
    map: sourcemap ? code.generateMap({hires: true}) : null
  };

  function getReturn() {
    if (!exportBindings.size) {
      return "";
    }
    if (exportBindings.size === 1 && exportBindings.has("default")) {
      return `return ${exportBindings.get("default")};\n`;
    }
    return `return {\n${
      [...exportBindings.entries()]
        .map(([left, right]) => `  ${left}: ${getName(right)}`)
        .join(",\n")
    }\n};\n`;

    function getName(name) {
      if (Array.isArray(name)) {
        return getBindingName(name);
      }
      return name;
    }
  }

  function getPrefix() {
    return exportBindings.size ? `var ${name} = ` : "";
  }

  function getBindingName([prop, source]) {
    if (prop === "default") {
      return resolveGlobal(source);
    }
    return `${resolveGlobal(source)}.${prop}`;
  }

  function overwriteVar(node, parent, name) {
    if (node.name === name || node.isOverwritten) {
      return;
    }
    if (parent.type === "Property" && parent.key.start === parent.value.start) {
      code.appendLeft(node.end, `: ${name}`);
      parent.key.isOverwritten = true;
      parent.value.isOverwritten = true;
    } else {
      code.overwrite(node.start, node.end, name, {contentOnly: true});
      // with object shorthand, the node would be accessed twice (.key and .value)
      node.isOverwritten = true;
    }
  }

  function createResolveGlobal(resolveGlobal) {
    const cache = new Map;

    return name => {
      if (!cache.has(name)) {
        cache.set(name, resolveGlobal(name) || camelcase(name));
      }
      return cache.get(name);
    };
  }
}

module.exports = {transform};