import argparse
import base64
import json
import secrets

import yaml
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import padding, rsa
from flask import Flask, redirect, render_template, request, session, url_for

parser = argparse.ArgumentParser()
parser.add_argument("config", help="Path to configuration file")
args = parser.parse_args()

with open(args.config) as f:
    config = yaml.safe_load(f)

app = Flask(__name__)
app.secret_key = config["secret_key"]

private_key = rsa.generate_private_key(public_exponent=65537, key_size=2048)


@app.route("/")
def index():
    return render_template("index.html", application_name=config["application_name"])


@app.route("/authorize")
def authorize():
    public_key = private_key.public_key().public_bytes(
        serialization.Encoding.PEM,
        serialization.PublicFormat.SubjectPublicKeyInfo,
    ).decode()

    nonce = secrets.token_hex(16)
    client_id = secrets.token_hex(48)
    session["nonce"] = nonce
    session["client_id"] = client_id

    params = {
        "auth_redirect": config["redirect_url"],
        "application_name": config["application_name"],
        "scopes": "read",
        "client_id": client_id,
        "nonce": nonce,
        "public_key": public_key,
    }
    query = "&".join(f"{k}={v}" for k, v in params.items())
    return redirect(f"{config['forum_url']}/user-api-key/new?{query}")


@app.route("/callback")
def callback():
    payload_b64 = request.args.get("payload")
    if not payload_b64:
        return "Missing payload", 400

    try:
        payload = base64.b64decode(payload_b64)
        data = private_key.decrypt(payload, padding.PKCS1v15())
        response = json.loads(data)
    except Exception:
        return "Failed to decrypt or decode payload", 400

    if response.get("nonce") != session.get("nonce"):
        return "Invalid nonce", 400

    key = response["key"]
    calendar_url = f"{config['forum_url']}/discourse-post-event/events.ics?order=desc&api_key={key}"

    return render_template(
        "result.html",
        application_name=config["application_name"],
        calendar_url=calendar_url,
    )


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=8000)