users_controller.rb

require 'securerandom'

class UsersController < ApplicationController
  before_filter :check_user, only: [:new]
  helper_method :state_parameter
  # GET /users
  # GET /users.json
  def index
    @users = User.all

    respond_to do |format|
      format.html # index.html.erb
      format.json { render json: @users }
    end
  end

  # GET /users/1
  # GET /users/1.json
  def show
    @user = User.find(params[:id])

    respond_to do |format|
      format.html # show.html.erb
      format.json { render json: @user }
    end
  end

  # GET /users/new
  # GET /users/new.json
  def new
    @user = User.new

    respond_to do |format|
      format.html # new.html.erb
      format.json { render json: @user }
    end
  end

  # GET /users/1/edit
  def edit
    @user = User.find(params[:id])
  end

  # POST /users
  # POST /users.json
  def create
    @user = User.find_or_create_from_auth_hash(request.env['omniauth.auth'])

    respond_to do |format|
      if @user.save
        if @user.persisted?
          notice = "User was logged in."
        else
          notice = "User was created."
        end
        session[:user] = @user.id
        format.html { redirect_to @user, notice: notice }
        format.json { render json: @user, status: :created, location: @user }
      else
        format.html { render action: "new" }
        format.json { render json: @user.errors, status: :unprocessable_entity }
      end
    end
  end

  # PUT /users/1
  # PUT /users/1.json
  def update
    @user = User.find(params[:id])

    respond_to do |format|
      if @user.update_attributes(params[:user])
        format.html { redirect_to @user, notice: 'User was successfully updated.' }
        format.json { head :no_content }
      else
        format.html { render action: "edit" }
        format.json { render json: @user.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /users/1
  # DELETE /users/1.json
  def destroy
    @user = User.find(params[:id])
    @user.destroy

    respond_to do |format|
      format.html { redirect_to users_url }
      format.json { head :no_content }
    end
  end

  def logout
    session.delete :user
    redirect_to new_user_path
  end

  protected

    def state_parameter
      session['omniauth.state'] = SecureRandom.hex(24)
    end

    def check_user
      if session[:user]
        @user = User.find(session[:user])
        redirect_to user_path(@user) if @user
      end
    end
end