main.py

import firebase_admin
import os
import random
import string

from typing import Annotated
from google.cloud import firestore
from google.cloud.exceptions import Conflict
from fastapi import FastAPI, HTTPException, Path
from fastapi.responses import RedirectResponse, Response

DATABASE = os.getenv("DATABASE")  # Datastore Database
COLLECTION = os.getenv("COLLECTION")  # Datastore Database Collection (table)

app = FastAPI()
firebase_init = firebase_admin.initialize_app()

db = firestore.Client(database=DATABASE)
collection = db.collection(COLLECTION)


@app.get("/{url_id}")
def get_smol_url(
    url_id: Annotated[str, Path(min_length=4, max_length=4, pattern="[a-zA-Z0-9]{4}")]
) -> RedirectResponse:
    """
    Retrieve the original URL for a given shortened URL identifier and redirect to it.

    Args:
        url_id (str): The unique identifier of the shortened URL.

    Raises:
        HTTPException: An exception with status code 404 if the URL is not found in the database.

    Returns:
        RedirectResponse: A redirection to the original URL associated with the given `url_id`.
    """
    hit = collection.document(url_id).get().to_dict()

    if not hit:
        raise HTTPException(status_code=404, detail="Url not found.")
    return RedirectResponse(hit["url"], status_code=302)


@app.post("/")
def create_smol_url(url: str) -> Response:
    """
    Create a new shortened URL that redirects to the supplied original URL.

    Args:
        url (str): The original URL that needs to be shortened.

    Raises:
        HTTPException: An exception with status code 500 indicating a need to retry the request due to a conflict (e.g., duplicate id).

    Returns:
        Response: the newly generated shortend URL.
    """
    raise HTTPException(status_code=500, detail="Not Implemented.")

    try:
        url_id = create_url_id()
        while collection.document(url_id).get().exists:
            url_id = create_url_id()

        collection.document(url_id).create({"url": url})

    except Conflict:
        raise HTTPException(status_code=500, detail="Retry Request.")

    return Response(status_code=200, content="/" + url_id)


def create_url_id() -> str:
    """
    Generate a random, unique identifier for a new shortened URL.

    The identifier consists of a string composed of 4 randomly chosen alphanumeric characters.

    Returns:
        str: A string representing the unique identifier for a shortened URL.
    """
    return "".join(
        random.SystemRandom().choices(string.ascii_letters + string.digits, k=4)
    )