import json
import os
import uuid

from flask import Flask, render_template, request, redirect
from werkzeug.wsgi import DispatcherMiddleware

import wccg


def create_redirecting_app(to):
    """Creates a dummy flask app which redirects to 'to' for the root url."""
    app = Flask('redirector')

    @app.route('/')
    def index():
        return redirect(to, code=301)

    return app


def create_app():
    """Initializes the Flask app.

    Reads the environment variable APPLICATION_ROOT and creates a
    DispatcherMiddleware if it is set to something different than /.
    This allows to mount the app in a subdirectory.
    """
    app = Flask(__name__)
    app.config['APPLICATION_ROOT'] = os.environ.get('APPLICATION_ROOT', '/')

    if app.config['APPLICATION_ROOT'] != '/':
        if app.config['APPLICATION_ROOT'].endswith('/'):
            app.config['APPLICATION_ROOT'] = app.config['APPLICATION_ROOT'][:-1]

        redirector = create_redirecting_app(app.config['APPLICATION_ROOT'])
        mounts = {
            app.config['APPLICATION_ROOT']: app.wsgi_app
        }
        app.wsgi_app = DispatcherMiddleware(redirector, mounts)

    app.logger.info('APPLICATION_ROOT=%s', app.config['APPLICATION_ROOT'])

    return app


app = create_app()


def create_response(sentence):
    """Prepares a response.

    Parses the sentence using wccg, then enriches the result with
    some meta data.

    Args:
        sentence: The sentence to parse.
    Returns:
        The response as a dictionary.
    """
    content = wccg.parse(sentence)

    response = {
        'version': '2.2.0',
        'application': 'web-openccg',
        'uuid': str(uuid.uuid4())
    }
    response.update(content)
    response.update(graphs.create_graphs(response['json_parses']))

    return response


@app.route('/parse', methods=['POST'])
def parse():
    """Handles parse requests.

    If the requests is a GET request or contains no POST data,
    an error (501 or 400, respectively) is returned.

    Otherwise, the sentence's parse is returned. If wccg was unable to parse
    the sentence, its answer is returned alongside a 422 status code.
    """
    if request.method == 'GET':
        return json.dumps(dict(error="Use POST.", http_status=501)), 501

    try:
        key = next(request.values.keys())
    except StopIteration:
        key = None

    # Get sentence from form field or use the first key.
    # The first key could be send e.g. by
    #     curl --data "This is the sentence." 127.0.0.1:5000/parse
    sentence = request.form.get(key) or key
    response = create_response(sentence)

    return json.dumps(response), response['http_status']


@app.route('/use')
def use():
    return render_template('use.html')


@app.route('/', methods=['GET', 'POST'])
def index():
    """This method shows a minimal user interface."""
    if request.method == 'POST':
        sentence = request.form.get('sentence')
        response = create_response(sentence)
        response = json.dumps(response, indent=4)
    else:
        sentence = None
        response = None
    return render_template('form.html', sentence=sentence, response=response)


if __name__ == '__main__':
    app.run(debug=True, host='0.0.0.0')