#models/like.rb
class Like < ActiveRecord::Base
  belongs_to :tweet
  belongs_to :user
  validates :user_id, presence: true
  validates :tweet_id, presence: true
end

#models/tweet.rb
class Tweet < ActiveRecord::Base
  belongs_to :user
  validates :text, presence: true, length: { maximum: 140 }
end

#models/user.rb
class User < ActiveRecord::Base
  has_many :tweets
  has_many :likes
  validates :email, presence: true, uniqueness: true
  validates :password, presence: true, length: { minimum: 6, maximum: 25 }
  validates :name, presence: true, uniqueness: true, format: { with: /\A[a-zA-Z0-9]+\Z/ }
end

#views/tweets/show.html.erb
<p id="notice"><%= notice %></p>

<p>
  <strong>Text:</strong>
  <%= @tweet.text %>
</p>

<p>
  <strong>User:</strong>
  <%= @tweet.user.name %>
</p>

<p>
  <%= link_to 'Like', @tweet.like %>
</p>

<%= link_to 'Edit', edit_tweet_path(@tweet) %> |
<%= link_to 'Back', tweets_path %>

#controllers/tweets_controller.rb
class TweetsController < ApplicationController
  before_action :set_tweet, only: [:show, :edit, :update, :destroy]

  # GET /tweets
  # GET /tweets.json
  def index
    @tweets = Tweet.all
  end

  # GET /tweets/1
  # GET /tweets/1.json
  def show
  end

  # GET /tweets/new
  def new
    @tweet = Tweet.new
  end

  # GET /tweets/1/edit
  def edit
  end

  # POST /tweets
  # POST /tweets.json
  def create
    @tweet = Tweet.new(tweet_params)

    respond_to do |format|
      if @tweet.save
        format.html { redirect_to @tweet, notice: 'Tweet was successfully created.' }
        format.json { render :show, status: :created, location: @tweet }
      else
        format.html { render :new }
        format.json { render json: @tweet.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /tweets/1
  # PATCH/PUT /tweets/1.json
  def update
    respond_to do |format|
      if @tweet.update(tweet_params)
        format.html { redirect_to @tweet, notice: 'Tweet was successfully updated.' }
        format.json { render :show, status: :ok, location: @tweet }
      else
        format.html { render :edit }
        format.json { render json: @tweet.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /tweets/1
  # DELETE /tweets/1.json
  def destroy
    @tweet.destroy
    respond_to do |format|
      format.html { redirect_to tweets_url, notice: 'Tweet was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  def like
    @tweet.likes.new(params[:user_id, :tweet_id])
    respond_to do |format|
      if @tweet.like.save
        format.html { redirect_to @tweet, notice: 'Like succeded.'}
        format.json { render :show, status: :ok, location: @tweet }
      else
        @tweet.like.destroy
        format.html { render :edit, notice: 'You dont like this anymore' }
        format.json { render json: @tweet.like.errors, status: :unprocessable_entity }
      end
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_tweet
      @tweet = Tweet.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def tweet_params
      params.require(:tweet).permit(:text, :user_id)
    end
end