text: from datetime import datetime
  
  from flask import render_template, flash, redirect, url_for, request
  from flask_login import current_user, login_user, logout_user, login_required
  from werkzeug.urls import url_parse
  from app import app, db
  from app.forms import LoginForm, RegistrationForm, EditProfileForm, PostForm
  from app.models import User, Post
  
  @app.before_request
  def before_request():
      if current_user.is_authenticated:
          current_user.last_seen = datetime.utcnow()
          db.session.commit()
  
  @app.route('/', methods=['GET', 'POST'])
  @app.route('/index', methods=['GET', 'POST'])
  @login_required
  def index():
      form = PostForm()
      if form.validate_on_submit():
          post = Post(body=form.post.data, author=current_user)
          db.session.add(post)
          db.session.commit()
          flash("Your post is now live.")
          return redirect(url_for('index'))
      #
      page = request.args.get('page', 1, type=int)
      posts = current_user.followed_posts().paginate( page, app.config['POSTS_PER_PAGE'], False)
      next_url = url_for('index', page=posts.next_num) if posts.has_next else None
      prev_url = url_for('index', page = posts.prev_num) if posts.has_prev else None
      return render_template('index.html', title='Home', form=form, posts=posts.items, prev_url=prev_url, next_url=next_url)
  
  
  @app.route('/login', methods=['GET', 'POST'])
  def login():
      if current_user.is_authenticated:
          return redirect(url_for('index'))
      form = LoginForm()
      if form.validate_on_submit():
          user = User.query.filter_by(username=form.username.data).first()
          if user is None or not user.check_password(form.password.data):
              flash('Invalid username or password')
              return redirect(url_for('login'))
          login_user(user, remember=form.remember_me.data)
          next_page = request.args.get('next')
          if not next_page or url_parse(next_page).netloc != '':
              next_page = url_for('index')
          return redirect(next_page)
      return render_template('login.html',  title='Sign In', form=form)
  
  @app.route('/logout')
  def logout():
      logout_user()
      return redirect(url_for('login'))
  
  @app.route('/register', methods=['GET', 'POST'])
  def register():
      if current_user.is_authenticated:
          return redirect(url_for('index'))
      form = RegistrationForm()
      if form.validate_on_submit():
          user = User(username=form.username.data, email=form.email.data)
          user.set_password(form.password.data)
          db.session.add(user)
          db.session.commit()
          flash('Congratulations, you are now a registered user!')
          return redirect(url_for('login'))
      return render_template('register.html', title='Register', form=form)
  
  @app.route('/user/<username>')
  @login_required
  def user(username):
      user = User.query.filter_by(username=username).first_or_404()
      page = request.args.get('page', 1, type=int)
      posts = user.posts.order_by(Post.timestamp.desc()).paginate( page, app.config['POSTS_PER_PAGE'], False)
      next_url = url_for('user', username=user.username, page=posts.next_num) if posts.has_next else None
      prev_url = url_for('user', username=user.username, page=posts.prev_num) if posts.has_prev else None
      return render_template('user.html', user=user, posts=posts.items, next_url=next_url, prev_url=prev_url)
  
  @app.route('/edit_profile', methods=['GET', 'POST'])
  @login_required
  def edit_profile():
      form = EditProfileForm(current_user.username)
      if form.validate_on_submit():
          current_user.username = form.username.data
          current_user.about_me = form.about_me.data
          db.session.commit()
          flash('Your changes have been saved.')
          return redirect(url_for('edit_profile'))
      elif request.method == 'GET':
          form.username.data = current_user.username
          form.about_me.data = current_user.about_me
      return render_template('edit_profile.html', title='Edit Profile', form=form)
  
  @app.route('/follow/<username>')
  @login_required
  def follow(username):
      user = User.query.filter_by(username=username).first()
      if user is None:
          flash(f'User {username} not found.')
          return redirect(url_for('index'))
      if user == current_user:
          flash(f'You cannot follow yourself.')
          return redirect(url_for('user', username=username))
      current_user.follow(user)
      db.session.commit()
      flash(f'you are following {username}.')
      return redirect(url_for('user', username=username))
  
  @app.route('/unfollow/<username>')
  @login_required
  def unfollow(username):
      user = User.query.filter_by(username=username).first()
      if user is None:
          flash(f'User {username} not found.')
          return redirect(url_for('index'))
  
      if user == current_user:
          flash(f'You cannot unfollow yourself.')
          return redirect(url_for('user', username=username))
      current_user.unfollow(user)
      db.session.commit()
      flash(f'you are not following {username}.')
      return redirect(url_for('user', username=username))
  
  @app.route('/explore')
  @login_required
  def explore():
      page = request.args.get('page', 1, type=int)
      posts = Post.query.order_by(Post.timestamp.desc()).paginate(
          page, app.config['POSTS_PER_PAGE'], False)
      next_url = url_for('explore', page=posts.next_num) if posts.has_next else None
      prev_url = url_for('explore', page = posts.prev_num) if posts.has_prev else None
      return render_template("index.html", title='Explore', posts=posts.items, prev_url=prev_url, next_url=next_url)
  