application_controller.rb

class Api::V1::ApplicationController < ApplicationController
  before_filter :authenticate_user!
  respond_to    :json
end

users_controller.rb

class Api::V1::UsersController < Api::V1::ApplicationController
  def index
    @users = User.all
    logger.info "API v1: Listed all users"
  end

  def show
    @user = User.find_by_id(params[:id])
    logger.info "API v1: Listed individual user: #{@user.authentication_token}"
  end

  def create
    if request.format != :json
      render :status => 406, :json => {:message => "The request must be json"}
      return
    end

    if params[:email].nil? or params[:password].nil? 
      render :status => 400, :json => {:message => "The request must contain the user email and password."}
      return
    end

    @user = User.find_by_email(params[:email])
    if @user.nil?
      @user = User.create(:email => params[:email], :password => params[:password])
      logger.info "API v1: Created user id: #{@user.id} successfully"
      render :status => 200, :json => {:id => @user.authentication_token} 
    end
    
    if @user.email and @user.valid_password?(params[:password]) 
      logger.info "API v1: Listed individual user: #{@user.id}"
      render :status => 200, :json => {:id => @user.authentication_token} 
    else
      logger.info("User #{@user.id} failed signin, password \"#{params[:password]}\" is invalid")
      render :status => 401, :json => {:message => "Invalid email or password."} 
    end

  end

  def update    
    @user = User.find_by_id(params[:id])
    if @user.nil?
      logger.info("User not found.")
      render :status => 404, :json => {:message => "Invalid user."}
    else
      @user.update_attributes(:name => params[:name], :email => params[:email], :password => params[:password])
      logger.info "API v1: Updated user #{@user.id} successfully"
      render :status => 200, :json => {:email => @user.authentication_token}
    end

  end

  def destroy
    @user = User.find_by_id(params[:id])
    if @user.nil?
      logger.info("User not found.")
      render :status => 404, :json => {:message => "Invalid user."}
    else
      @user.destroy
      logger.info "API v1: Destroyed user #{@user.authentication_token} successfully"
      render :status => 200, :json => {:id => params[:id]}
    end
  end
  
  def email
    @user = User.find_by_id(params[:id])
    @user.update_attributes(:email => params[:email])
    logger.info "API v1: Saved individual user: #{@user.authentication_token}'s email"
  end
end