Get the file ID of a Library - google-apps-script

Question

The basic case is 2 files:
Admin file. Library.
User file.
I use a library file as admin file, and store some settings on its sheet. In a User file, I have a code, that needs an access to Admin file.
The code in a library:
SpreadsheetApp.getActive();
won't work, it will return the User file when running from a library.
Is there a code to have an access to a library file (spreadsheet)?
I need this because do not want to hardcode the ID of a library, in order to make it work with different copies of a library file.
I think of a solution similar to Excel's:
Set book = ThisWorkbook
The code in Excel will always return file where the code is.

Answer 1

How about this sample script? Recently, Google Apps Script API was added. By this, users can easily manage GAS project files. This sample script uses this API.
In order to use this sample script, please do the following flow.
Installation
Enable Google Apps Script API at API console.
If you have already opened the script editor, you can access there by this link.
Retrieve current scopes.
On script editor, File -> Project properties -> Scopes
Copy scopes.
Add a scope of https://www.googleapis.com/auth/script.projects to the Manifests file (appsscript.json) of the script editor. https://www.googleapis.com/auth/script.projects.readonly may be able to be also used in this situation.
On script editor, View -> Show manifest file
Add "oauthScopes": ["https://www.googleapis.com/auth/script.projects", "https://www.googleapis.com/auth/script.external_request", "### other scopes ###"] to appsscript.json, and save.
In this sample, https://www.googleapis.com/auth/script.external_request is also required.
If your script needs other scopes, please add them here.
Copy and paste this sample script, and run. And please authorize.
Please input Identifier for the library and fileId of project file that the library was installed.
Sample script :
function fetch(id) {
var url = "https://script.googleapis.com/v1/projects/" + id + "/content";
var params = {
method: "get",
headers: {"Authorization": "Bearer " + ScriptApp.getOAuthToken()},
muteHttpExceptions: true
};
return JSON.parse(UrlFetchApp.fetch(url, params).getContentText()).files;
}
function main() {
var Identifier = "### Identifier ###"; // Identifier for the library.
var fileId = "### fileId ###"; // fileId of project file that the library was installed.
var files = fetch(fileId);
var library = files.filter(function(e){return (e.type == "JSON" && e.name == "appsscript")})[0];
var source = JSON.parse(library.source);
var libraryId = source.dependencies.libraries.filter(function(e){return e.userSymbol == Identifier})[0].libraryId;
var libraryCode = fetch(libraryId);
Logger.log(libraryCode)
}
Note :
The flow of this sample script is as follows.
Retrieve the library ID from fileId of project file that the library was installed.
Retrieve the library code from the library ID.
The result of libraryCode is json data. This data is raw data of project. You can retrieve the library code from it.
References :
Google Apps Script API
Manifests
If I misunderstand your question, I'm sorry.
Edit :
Unfortunately, in current stage, I think that it cannot achieve to retrieve Spreadsheet ID that the library was installed under the situation.