import base64
import secrets
import importlib
from flask import Flask

from .common.common import *
from .common.user import init_login

app = Flask(__name__)
app.secret_key = base64.b64decode(cf['frontend'].get('secret_key','')) or \
    secrets.token_bytes(16) # development fallback; CSRF/cookies won't persist.
init_login(app)

for name in cf['frontend']['modules'].split(','):
    blueprint = importlib.import_module('.'+name, __name__)
    app.register_blueprint(blueprint.frontend)


# TODO: should this go somewhere else?
# This error handler logs requests to external apis. this makes debugging of api responses easier, as the request can be reconstructed and replayed.
from flask import g
from werkzeug.exceptions import InternalServerError
@app.errorhandler(InternalServerError)
def log_errors(e):
    if 'api_requests' in g:
        app.logger.error(g.api_requests)
    return e

# TODO: build a proper flask extension
# Magic CSRF protection: This modifies outgoing HTML responses and injects a csrf token into all forms.
# All post requests are then checked if they contain the valid token.
# TODO:
# - don't use regex for injecting
# - inject a http header into all responses (that could be used by apis)
# - allow csrf token to be passed in http header, json, ...
# - a decorator on routes to opt out of verification or output munging
#   https://stackoverflow.com/questions/19574694/flask-hit-decorator-before-before-request-signal-fires
# - allow specifying hmac message contents (currently request.remote_addr)
import re
import hmac
import hashlib
from flask import request
@app.after_request
def add_csrf_protection(response):
    if response.mimetype == "text/html":
        token = hmac.new(app.secret_key, request.remote_addr.encode('ascii'), hashlib.sha256).hexdigest()  # TODO: will fail behind reverse proxy (remote_addr always localhost)
        response.set_data( re.sub(
            rb'''(<[Ff][Oo][Rr][Mm](\s+[a-zA-Z0-9-]+(=(\w*|'[^']*'|"[^"]*"))?)*>)''', # match form tags with any number of attributes and any type of quotes
            rb'\1<input type="hidden" name="csrf" value="'+token.encode('ascii')+rb'">', # hackily append a hidden input with our csrf protection value
            response.get_data()))
    return response
@app.before_request
def verify_csrf_protection():
    token = hmac.new(app.secret_key, request.remote_addr.encode('ascii'), hashlib.sha256).hexdigest()  # TODO: will fail behind reverse proxy (remote_addr always localhost)
    if request.method == "POST" and request.form.get('csrf') != token:
        return "CSRF validation failed!", 400
    request.form = request.form.copy() # make it mutable
    request.form.poplist('csrf')  # remove our csrf again