import * as t from "babel-types";

// this function converts a shorthand object generator method into a normal
// (non-shorthand) object property which is a generator function expression. for
// example, this:
//
//  var foo = {
//    *bar(baz) { return 5; }
//  }
//
// should be replaced with:
//
//  var foo = {
//    bar: function*(baz) { return 5; }
//  }
//
// to do this, it clones the parameter array and the body of the object generator
// method into a new FunctionExpression.
//
// this method can be passed any Function AST node path, and it will return
// either:
//   a) the path that was passed in (iff the path did not need to be replaced) or
//   b) the path of the new FunctionExpression that was created as a replacement
//     (iff the path did need to be replaced)
//
// In either case, though, the caller can count on the fact that the return value
// is a Function AST node path.
//
// If this function is called with an AST node path that is not a Function (or with an
// argument that isn't an AST node path), it will throw an error.
export default function replaceShorthandObjectMethod(path) {
  if (!path.node || !t.isFunction(path.node)) {
    throw new Error("replaceShorthandObjectMethod can only be called on Function AST node paths.");
  }

  // this function only replaces shorthand object methods (called ObjectMethod
  // in Babel-speak).
  if (!t.isObjectMethod(path.node)) {
    return path;
  }

  // this function only replaces generators.
  if (!path.node.generator) {
    return path;
  }

  const parameters = path.node.params.map(function (param) {
    return t.cloneDeep(param);
  })

  const functionExpression = t.functionExpression(
    null, // id
    parameters, // params
    t.cloneDeep(path.node.body), // body
    path.node.generator,
    path.node.async
  );

  path.replaceWith(
    t.objectProperty(
      t.cloneDeep(path.node.key), // key
      functionExpression, //value
      path.node.computed, // computed
      false // shorthand
    )
  );

  // path now refers to the ObjectProperty AST node path, but we want to return a
  // Function AST node path for the function expression we created. we know that
  // the FunctionExpression we just created is the value of the ObjectProperty,
  // so return the "value" path off of this path.
  return path.get("value");
}
