class Post < ApplicationRecord

  validates :content, {presence: true, length: {maximum: 140}}
  validates :user_id, {presence: true}
  has_many :comments

  def user
    return User.find_by(id: self.user_id)
  end

end

class User < ApplicationRecord
  has_secure_password
  validates :name, {presence: true}
  validates :email, {presence: true, uniqueness: true}
  has_many :comments

  def posts
    return Post.where(user_id: self.id)
  end



end

class Comment < ApplicationRecord
  belongs_to :user
  belongs_to :post, optional: true
end

class CommentsController < ApplicationController

   before_action :authenticate_user!

  def create
    post = Post.find(params[:post_id])
    @comment = post.comments.build(comment_params)
    @comment.user_id = current_user.id
    if @comment.save
      flash[:success] = "コメントしました"
      redirect_back(fallback_location: root_path)
    else
      flash[:success] = "コメントできませんでした"
      redirect_back(fallback_location: root_path)
    end
  end

  private
    def comment_params
      params.require(:comment).permit(:content)
    end
end

class PostsController < ApplicationController
    before_action :authenticate_user
    before_action :ensure_correct_user, {only: [:edit, :update, :destroy]}

  def index
    @posts = Post.all.order(created_at: :desc)
  end

  def show
    @post = Post.find_by(id: params[:id])
    @user = @post.users　←ここでエラーが出ます。
    @post = Post.find(params[:id])
    @comments = @post.comments
    @comment = @post.comments.build
  end

  def new
      @post = Post.new
  end

  def create
    @post = Post.new(
      content: params[:content],
      user_id: @current_user.id
      )
    if @post.save
      flash[:notice] = "投稿を作成しました"
     redirect_to("/posts/index")
    else
     render("posts/new")
    end
  end

 def edit
  @post = Post.find_by(id: params[:id])
 end

 def update
 @post = Post.find_by(id: params[:id])
 @post.content = params[:content]
 if @post.save
   flash[:notice] = "投稿を編集しました"
   redirect_to("/posts/index")
 else
   render("posts/edit")
 end
 end

 def destroy
   @post = Post.find_by(id: params[:id])
   @post.destroy
   flash[:notice] = "投稿を削除しました"
   redirect_to("/posts/index")
 end

 def ensure_correct_user
     @post = Post.find_by(id: params[:id])
     if @post.user_id != @current_user.id
         flash[:notice] = "権限がありません"
         redirect_to("/posts/index")
     end
 end

end

Rails.application.routes.draw do

  get "login" => "users#login_form"


  post "login" => "users#login"
  post "logout" => "users#logout"


  post "users/:id/update" => "users#update"
  get "users/:id/edit" => "users#edit"
  post "users/create" => "users#create"
  get "singnup" => "users#new"
  get "users/index" => "users#index"
  get "users/:id" => "users#show"

  get "posts/index" => "posts#index"
  get "posts/new" => "posts#new"
  get "posts/:id" => "posts#show"

  resources :posts do
    resources :comments, only: [:create]
  end

  post "posts/create" => "posts#create"
  get "posts/:id/edit" => "posts#edit"
  post "posts/:id/update" => "posts#update"
  post "posts/:id/destroy" => "posts#destroy"
  get "/" => "home#top"
  get "about" => "home#about"

end

<div class="main posts-show">
  <div class="container">
    <div class="posts-show-item">
      <div class="post-user-name">
        <img src="<%= "/user_images/#{@user.image_name}" %>">
        <%= link_to(@user.name, "/users/#{@user.id}") %>
      </div>
      <p>
        <%= @post.content %>
      </p>

      <div class="post-time">
       <%= @post.created_at %>
       </div>
       <% if @post.user_id == @current_user.id %>
       <div class="post-menus">
        <%= link_to("編集", "/posts/#{@post.id}/edit") %>
        <%= link_to("削除", "/posts/#{@post.id}/destroy", {method: "post"}) %>
      </div>
      <% end %>
    </div>
  </div>
</div>

#これから下がcommentコードです。
<div class="comment-wrapper border-top　mb-10">
  <p class="mt-5">コメント一覧</p>
  <% @comments.each do |c| %>
    <div>
      <% unless c.user.blank? %>
        <a href="<%= user_path(c.user_id) %>"><%= image_tag c.user.image.to_s,
          class:"rounded-circle icon_image mr-3 mb-3"%></a>
        <% end %>
      <%= c.user.username unless c.user.blank? %>
      <br />
      <%= c.content %>
    </div>
    <br />
  <% end %>
  <% if user_signed_in? %>
    <%= form_with(model: [@post, @comment], local: true) do |f| %>
      <%= f.text_area :content, class: "form-control", rows: 5 %>
      <%= button_tag type: "submit", class: "btn btn-success float-right mt-1" do %>
        <i class="far fa-comments"></i> コメントする
      <% end %>
    <% end %>
  <% end %>
</div>