"""Team Tryouts Application - Flask Application Factory.

This module provides the application factory for creating and configuring
the Flask application instance with comprehensive security hardening.
"""

import os
import secrets

from flask import Flask, g, request, redirect, jsonify, render_template, url_for
from flask_cors import CORS
from app.extensions import db, login_manager, csrf, limiter, babel
from sqlalchemy import text
from werkzeug.exceptions import HTTPException
import markupsafe
from dotenv import load_dotenv
from app import i18n

load_dotenv()


def nl2br(value):
    """Convert newlines to HTML line breaks.

    Args:
        value: String value to convert.

    Returns:
        Markup: HTML-safe string with line breaks.
    """
    if value:
        # Markup('<br>').join() escapes each segment before joining.
        # Markup('<br>'.join(...)) would mark attacker-controlled text as safe.
        return markupsafe.Markup('<br>').join(str(value).splitlines())
    return ''


def build_csp(*, allow_inline_script, nonce=None):
    """Assemble the Content-Security-Policy header.

    Two mutually exclusive modes, and they really are exclusive.

    Under CSP level 3, a browser that understands nonces **ignores
    'unsafe-inline' entirely as soon as a nonce is present**. Emitting both
    would therefore not be a gentle transition: it would drop every inline
    script and every onclick attribute at once, in modern browsers only.
    The switch has to be atomic, which is why one flag drives it.

    While allow_inline_script is true no nonce is emitted at all, so adding
    nonce="{{ csp_nonce }}" to a template ahead of the switch is harmless.

    Flipping the flag requires every inline event handler to be gone first.
    A nonce cannot authorise an onclick attribute — nonces apply to script
    elements, never to handler attributes. See tests/test_csp.py, which
    tracks how many are left.

    Args:
        allow_inline_script: Keep 'unsafe-inline' in script-src.
        nonce: Per-request nonce, used only when inline script is not allowed.

    Returns:
        str: The header value.
    """
    if allow_inline_script:
        script_src = "'self' 'unsafe-inline' https://cdn.jsdelivr.net"
    else:
        script_src = f"'self' 'nonce-{nonce}' https://cdn.jsdelivr.net"

    return '; '.join([
        "default-src 'self'",
        f'script-src {script_src}',
        # style-src is a separate migration: inline style="" attributes are
        # spread across the templates and are not an XSS vector on their own.
        "style-src 'self' 'unsafe-inline' https://cdnjs.cloudflare.com https://cdn.jsdelivr.net",
        "font-src 'self' https://cdnjs.cloudflare.com",
        "img-src 'self' data: https://cdn.discordapp.com",
        "connect-src 'self'",
        "frame-ancestors 'none'",
        "base-uri 'self'",
        "form-action 'self'",
    ])


def create_app(config=None):
    """Create and configure the Flask application.

    Args:
        config: Optional mapping of configuration overrides, applied after the
            environment defaults and before validation. This is what makes the
            factory usable from tests: pass a throwaway database URI, a dummy
            secret, and turn off the Discord bot, without touching os.environ.

    Initializes Flask with:
        - Secret key for session security
        - Database configuration
        - CSRF protection
        - CORS with restricted origins
        - Login manager
        - Rate limiting
        - All route blueprints
        - Security headers and HTTPS redirects
        - Custom error handlers
        - Health check endpoint
        - Structured logging

    Handles database initialization and seeding with sample data if empty.

    Returns:
        Flask: Configured Flask application instance.
    """
    app = Flask(__name__)

    # --- defaults from the environment ------------------------------------
    app.config['SECRET_KEY'] = os.getenv('SECRET_KEY')
    app.config['SQLALCHEMY_DATABASE_URI'] = os.getenv('DATABASE_URL')
    app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False
    app.config['WTF_CSRF_ENABLED'] = True
    app.config['CORS_ALLOWED_ORIGINS'] = os.getenv('CORS_ALLOWED_ORIGINS', '')
    app.config['FORCE_HTTPS'] = os.getenv('FORCE_HTTPS', 'true').lower() == 'true'

    # Still true: 76 inline event handlers remain across the templates, and
    # no nonce can authorise those. Flip once tests/test_csp.py reports zero.
    app.config['CSP_ALLOW_INLINE_SCRIPT'] = (
        os.getenv('CSP_ALLOW_INLINE_SCRIPT', 'true').lower() == 'true'
    )

    # Internationalisation. French is the site's primary language.
    app.config['BABEL_DEFAULT_LOCALE'] = i18n.DEFAULT_LOCALE
    app.config['BABEL_TRANSLATION_DIRECTORIES'] = os.path.join(
        os.path.dirname(os.path.abspath(__file__)), 'translations'
    )

    # Side effects of create_app(), both on by default so that production and
    # development behave exactly as before. Tests turn them off.
    app.config['AUTO_CREATE_TABLES'] = (
        os.getenv('AUTO_CREATE_TABLES', 'true').lower() == 'true'
    )
    app.config['ENABLE_DISCORD_BOT'] = (
        os.getenv('ENABLE_DISCORD_BOT', 'true').lower() == 'true'
    )

    # --- caller overrides win ---------------------------------------------
    if config:
        app.config.update(config)

    # --- validation, after overrides so tests can supply their own ---------
    if not app.config['SECRET_KEY']:
        raise RuntimeError('SECRET_KEY environment variable must be set for security')
    if not app.config['SQLALCHEMY_DATABASE_URI']:
        raise RuntimeError(
            'DATABASE_URL environment variable must be set to a PostgreSQL connection string'
        )

    # File upload size limit (16 MB)
    app.config['MAX_CONTENT_LENGTH'] = 16 * 1024 * 1024

    # Secure session cookie settings
    app.config['SESSION_COOKIE_SECURE'] = os.getenv('SESSION_COOKIE_SECURE', 'true').lower() == 'true'
    app.config['SESSION_COOKIE_HTTPONLY'] = True
    app.config['SESSION_COOKIE_SAMESITE'] = 'Lax'
    app.config['PERMANENT_SESSION_LIFETIME'] = 3600  # 1 hour session timeout

    # Configure CORS - restrict to specific origins in production
    allowed_origins = str(app.config.get('CORS_ALLOWED_ORIGINS') or '').split(',')
    allowed_origins = [origin.strip() for origin in allowed_origins if origin.strip()]

    # CORS is only configured when origins are named explicitly.
    #
    # The previous else-branch called CORS(app, supports_credentials=True)
    # with no origins argument. flask-cors then defaults to '*' and, because
    # credentials are allowed, echoes back whatever Origin the caller sent
    # together with Access-Control-Allow-Credentials: true — the opposite of
    # the "allow all (development) or none (production)" the comment claimed.
    #
    # Exploitation was blocked by SESSION_COOKIE_SAMESITE = 'Lax', which stops
    # the browser attaching the session cookie to a cross-site fetch. That is
    # a single setting standing between a misconfiguration and a cross-origin
    # data leak. This application renders server-side HTML on one origin and
    # needs no CORS policy at all.
    if allowed_origins:
        CORS(
            app,
            origins=allowed_origins,
            supports_credentials=True,
            methods=['GET', 'POST', 'PUT', 'PATCH', 'DELETE', 'OPTIONS'],
            max_age=3600,  # Cache preflight for 1 hour
        )

    db.init_app(app)
    login_manager.init_app(app)
    csrf.init_app(app)
    limiter.init_app(app)
    babel.init_app(app, locale_selector=i18n.select_locale)

    # Exposed to every template so the language switcher can render itself
    # without each view having to pass the list along.
    @app.before_request
    def generate_csp_nonce():
        # Only meaningful once inline script is disallowed; generated
        # unconditionally so templates can carry nonce="" beforehand.
        g.csp_nonce = secrets.token_urlsafe(16)

    @app.context_processor
    def inject_csp_nonce():
        return {'csp_nonce': '' if app.config['CSP_ALLOW_INLINE_SCRIPT']
                             else g.get('csp_nonce', '')}

    @app.context_processor
    def inject_locales():
        from flask_babel import get_locale
        return {
            'current_locale': str(get_locale() or i18n.DEFAULT_LOCALE),
            'supported_locales': i18n.SUPPORTED_LOCALES,
            'locale_names': i18n.LOCALE_NAMES,
        }

    # Configure structured logging
    from app.logging_config import configure_logging
    configure_logging(app)

    from app.routes.auth import auth_bp
    from app.routes.tryouts import tryouts_bp
    from app.routes.evaluations import evaluations_bp
    from app.routes.users import users_bp
    from app.routes.main import main_bp
    from app.routes.teams import teams_bp
    from app.routes.matches import matches_bp
    from app.routes.team_matches import team_matches_bp

    app.register_blueprint(auth_bp)
    app.register_blueprint(tryouts_bp)
    app.register_blueprint(evaluations_bp)
    app.register_blueprint(users_bp)
    app.register_blueprint(main_bp)
    app.register_blueprint(teams_bp)
    app.register_blueprint(matches_bp)
    app.register_blueprint(team_matches_bp)

    # Register custom Jinja filters
    app.jinja_env.filters['nl2br'] = nl2br

    # =========================================================================
    # Security Headers
    # =========================================================================
    @app.after_request
    def add_security_headers(response):
        """Add security headers to all responses.

        Implements defense-in-depth with comprehensive HTTP security headers.
        These complement the headers set by Nginx in production.

        HSTS is only sent in production (non-debug) to avoid breaking
        local development over plain HTTP.
        """
        # X-XSS-Protection is deliberately not set: the auditor it addressed
        # has been removed from every current browser, and its last versions
        # introduced vulnerabilities of their own. CSP frame-ancestors and
        # X-Frame-Options cover the remaining ground.
        response.headers['X-Content-Type-Options'] = 'nosniff'
        response.headers['X-Frame-Options'] = 'DENY'
        response.headers['Referrer-Policy'] = 'strict-origin-when-cross-origin'
        response.headers['Permissions-Policy'] = (
            'camera=(), microphone=(), geolocation=(), '
            'interest-cohort=(), payment=(), usb=()'
        )
        response.headers['Cross-Origin-Opener-Policy'] = 'same-origin'
        response.headers['Content-Security-Policy'] = build_csp(
            allow_inline_script=app.config['CSP_ALLOW_INLINE_SCRIPT'],
            nonce=g.get('csp_nonce'),
        )

        # Only enable HSTS when HTTPS is actually being used
        # (either direct TLS or behind a proxy that terminates TLS)
        is_https = request.is_secure or request.headers.get('X-Forwarded-Proto') == 'https'
        if is_https:
            response.headers['Strict-Transport-Security'] = (
                'max-age=31536000; includeSubDomains; preload'
            )

        return response

    # =========================================================================
    # HTTPS Redirect (Production only)
    # =========================================================================
    @app.before_request
    def force_https():
        """Redirect all HTTP requests to HTTPS in production.

        Respects the X-Forwarded-Proto header from reverse proxies.
        Can be disabled via FORCE_HTTPS environment variable.
        """
        if not app.debug and app.config['FORCE_HTTPS']:
            if not request.is_secure and request.headers.get('X-Forwarded-Proto') != 'https':
                return redirect(request.url.replace('http://', 'https://'), code=301)

    # =========================================================================
    # Health Check Endpoint
    # =========================================================================
    @app.route('/health')
    def health_check():
        """Health check endpoint for monitoring and load balancers.

        Verifies database connectivity and application health.
        Returns 200 with basic status info or 503 if unhealthy.

        Returns:
            Response: JSON health status.
        """
        health_data = {
            'status': 'healthy',
            'app': 'team-tryouts',
            'version': '1.0.0',
        }

        # Check database connectivity
        try:
            db.session.execute(text('SELECT 1'))
            health_data['database'] = 'connected'
        except Exception:
            # Never echo the driver error: it routinely carries the host,
            # database name and user of the connection string, and /health
            # is unauthenticated.
            app.logger.error('Health check: database unreachable', exc_info=True)
            health_data['status'] = 'unhealthy'
            health_data['database'] = 'error'
            return jsonify(health_data), 503

        return jsonify(health_data), 200

    # =========================================================================
    # Custom Error Handlers
    # =========================================================================
    @app.errorhandler(400)
    def bad_request(error):
        """Handle 400 Bad Request errors.

        Args:
            error: The error object.

        Returns:
            Response: Rendered error page or JSON for API requests.
        """
        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/coach-availability') or \
           request.path.startswith('/users/api/'):
            return jsonify({'error': 'Bad request', 'message': str(error)}), 400
        return render_template('errors/400.html', error=error), 400

    @app.errorhandler(401)
    def unauthorized(error):
        """Handle 401 Unauthorized errors.

        Args:
            error: The error object.

        Returns:
            Response: Redirect to login for pages, JSON for API.
        """
        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/api/'):
            return jsonify({'error': 'Unauthorized'}), 401
        from flask import flash as _flash
        _flash('Please log in to access this page.', 'warning')
        return redirect(url_for('auth.login'))

    @app.errorhandler(403)
    def forbidden(error):
        """Handle 403 Forbidden errors.

        Args:
            error: The error object.

        Returns:
            Response: Rendered error page or JSON for API requests.
        """
        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/api/'):
            return jsonify({'error': 'Forbidden', 'message': str(error)}), 403
        return render_template('errors/403.html', error=error), 403

    @app.errorhandler(404)
    def not_found(error):
        """Handle 404 Not Found errors.

        Args:
            error: The error object.

        Returns:
            Response: Rendered error page or JSON for API requests.
        """
        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/api/'):
            return jsonify({'error': 'Not found'}), 404
        return render_template('errors/404.html', error=error), 404

    @app.errorhandler(429)
    def too_many_requests(error):
        """Handle 429 Too Many Requests errors.

        Args:
            error: The error object.

        Returns:
            Response: JSON error for API or rendered page.
        """
        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/api/'):
            return jsonify({
                'error': 'Too many requests',
                'message': 'Please try again later.'
            }), 429
        return render_template('errors/429.html', error=error), 429

    @app.errorhandler(500)
    def internal_error(error):
        """Handle 500 Internal Server Error.

        Never exposes stack traces to users. Logs the full error internally.

        Args:
            error: The error object.

        Returns:
            Response: Generic error page or JSON.
        """
        # Log the full error for debugging
        app.logger.error('Internal Server Error: %s', str(error), exc_info=True)

        # Roll back any failed database session
        db.session.rollback()

        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/api/'):
            return jsonify({
                'error': 'Internal server error',
                'message': 'An unexpected error occurred. Please try again later.'
            }), 500
        return render_template('errors/500.html'), 500

    @app.errorhandler(HTTPException)
    def handle_http_exception(error):
        """Catch-all handler for any unhandled HTTP exceptions.

        Args:
            error: The HTTPException object.

        Returns:
            Response: JSON error for API, re-raises for others.
        """
        if request.path.startswith('/users/disponibilities') or \
           request.path.startswith('/users/api/'):
            return jsonify({
                'error': error.name,
                'message': error.description,
                'code': error.code
            }), error.code
        return error

    # =========================================================================
    # Database Initialization
    # =========================================================================
    with app.app_context():
        import app.models as models  # noqa: F401 — registers all models with SQLAlchemy
        # NOTE: create_all() only ever creates missing tables. It never adds a
        # column to an existing one, so a model change is silently absent from
        # any database that already has the table. Replacing this with Alembic
        # is tracked as DB-002/DB-004; until then the behaviour is preserved.
        if app.config['AUTO_CREATE_TABLES']:
            db.create_all()

    # Start the Discord bot for notifications
    if app.config['ENABLE_DISCORD_BOT']:
        try:
            from app.discord_bot import start_bot
            start_bot(flask_app=app)
        except Exception as e:
            app.logger.warning('Could not start Discord bot: %s', e)

    return app


if __name__ == '__main__':
    # Only used for development - production uses wsgi.py (Waitress)
    app = create_app()
    debug_mode = os.getenv('FLASK_DEBUG', 'false').lower() == 'true'
    if debug_mode:
        app.logger.warning(
            'Running in DEBUG mode with Flask built-in server. '
            'This is NOT suitable for production. Use wsgi.py instead.'
        )
    app.run(debug=debug_mode, host='0.0.0.0', port=10000)