import { Message } from './message.js';

// Copyright 2021-2024 Buf Technologies, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
/**
 * Check whether the given object is any subtype of Message or is a specific
 * Message by passing the type.
 *
 * Just like `instanceof`, `isMessage` narrows the type. The advantage of
 * `isMessage` is that it compares identity by the message type name, not by
 * class identity. This makes it robust against the dual package hazard and
 * similar situations, where the same message is duplicated.
 *
 * This function is _mostly_ equivalent to the `instanceof` operator. For
 * example, `isMessage(foo, MyMessage)` is the same as `foo instanceof MyMessage`,
 * and `isMessage(foo)` is the same as `foo instanceof Message`. In most cases,
 * `isMessage` should be preferred over `instanceof`.
 *
 * However, due to the fact that `isMessage` does not use class identity, there
 * are subtle differences between this function and `instanceof`. Notably,
 * calling `isMessage` on an explicit type of Message will return false.
 */
function isMessage(arg, type) {
    if (arg === null || typeof arg != "object") {
        return false;
    }
    if (!Object.getOwnPropertyNames(Message.prototype).every((m) => m in arg && typeof arg[m] == "function")) {
        return false;
    }
    const actualType = arg.getType();
    if (actualType === null ||
        typeof actualType != "function" ||
        !("typeName" in actualType) ||
        typeof actualType.typeName != "string") {
        return false;
    }
    return type === undefined ? true : actualType.typeName == type.typeName;
}

export { isMessage };
