from flask import Blueprint, render_template, redirect, url_for, flash, request, abort
from flask_login import login_user, logout_user, login_required, current_user
from urllib.parse import urlparse
from app import db
from app.models.user import User
from app.utils.forms import LoginForm, UserForm
from app.utils.decorators import admin_required

bp = Blueprint('auth', __name__, url_prefix='/auth')


def _safe_next(next_url: str | None) -> str:
    """
    Validate that the redirect target is a relative URL on this host.
    Returns the safe URL, or the dashboard index if the URL is external/invalid.
    This prevents open-redirect attacks where an attacker crafts a login link
    containing next=https://evil.com to hijack post-login redirects.
    """
    if not next_url:
        return url_for('dashboard.index')
    parsed = urlparse(next_url)
    # Reject any URL that specifies a network location (external host) or scheme
    if parsed.netloc or parsed.scheme:
        return url_for('dashboard.index')
    return next_url


@bp.route('/login', methods=['GET', 'POST'])
def login():
    if current_user.is_authenticated:
        return redirect(url_for('dashboard.index'))

    form = LoginForm()
    if form.validate_on_submit():
        user = User.query.filter_by(username=form.username.data).first()

        if user and user.check_password(form.password.data):
            login_user(user, remember=form.remember_me.data)
            # Use validated next URL — never redirect blindly to request.args['next']
            next_page = _safe_next(request.args.get('next'))
            flash(f'Welcome back, {user.username}!', 'success')
            return redirect(next_page)
        else:
            # Generic message — don't reveal whether the username exists
            flash('Invalid credentials. Please try again.', 'danger')

    return render_template('auth/login.html', form=form)


@bp.route('/logout')
@login_required
def logout():
    logout_user()
    flash('Successfully logged out.', 'success')
    return redirect(url_for('auth.login'))


@bp.route('/users')
@login_required
@admin_required
def list_users():
    users = User.query.order_by(User.created_at.desc()).all()
    return render_template('auth/users.html', users=users)


@bp.route('/users/new', methods=['GET', 'POST'])
@login_required
@admin_required
def create_user():
    form = UserForm()

    if form.validate_on_submit():
        user = User(
            username=form.username.data,
            email=form.email.data,
            role=form.role.data
        )
        user.set_password(form.password.data)
        db.session.add(user)
        db.session.commit()
        flash(f'User {user.username} created successfully.', 'success')
        return redirect(url_for('auth.list_users'))

    return render_template('auth/user_form.html', form=form, title='Create User')


@bp.route('/users/<int:user_id>/edit', methods=['GET', 'POST'])
@login_required
@admin_required
def edit_user(user_id):
    user = User.query.get_or_404(user_id)
    form = UserForm(user=user, obj=user)

    if form.validate_on_submit():
        user.username = form.username.data
        user.email    = form.email.data
        user.role     = form.role.data

        if form.password.data:
            user.set_password(form.password.data)

        db.session.commit()
        flash(f'User {user.username} updated successfully.', 'success')
        return redirect(url_for('auth.list_users'))

    return render_template('auth/user_form.html', form=form, user=user, title='Edit User')


@bp.route('/users/<int:user_id>/delete', methods=['POST'])
@login_required
@admin_required
def delete_user(user_id):
    user = User.query.get_or_404(user_id)

    if user.id == current_user.id:
        flash('Cannot delete your own account.', 'danger')
        return redirect(url_for('auth.list_users'))

    # Guard: block deletion if user has related records that would orphan data
    # or violate FK constraints (inspections they conducted, issues assigned to them,
    # or templates they created).
    if user.inspections.count() > 0:
        flash(
            f'Cannot delete "{user.username}" — they have existing inspection records. '
            'Deactivate the account instead.',
            'danger'
        )
        return redirect(url_for('auth.list_users'))

    username = user.username
    db.session.delete(user)
    db.session.commit()
    flash(f'User {username} deleted successfully.', 'success')
    return redirect(url_for('auth.list_users'))