# Terminal
bundle add fast-mcp
bin/rails g fast_mcp:install
rails g model user name email age:integer
npx @modelcontextprotocol/inspector

# app/resources/application_resource.rb
# frozen_string_literal: true

class ApplicationResource < ActionResource::Base
  # write your custom logic to be shared across all resources here
end

# app/resources/sample_resource.rb
# frozen_string_literal: true

class SampleResource < ApplicationResource
  uri "examples/users"
  resource_name "Users"
  description "A user resource for demonstration"
  mime_type "application/json"

  def content
    JSON.generate(User.all.as_json)
  end
end

# app/tools/application_tool.rb
# frozen_string_literal: true

class ApplicationTool < ActionTool::Base
  # write your custom logic to be shared across all tools here
end

# app/tools/sample_tool.rb
# frozen_string_literal: true

class SampleTool < ApplicationTool
  description "Greet a user"

  arguments do
    required(:id).filled(:integer).description("ID of the user to greet")
    optional(:prefix).filled(:string).description("Prefix to add to the greeting")
  end

  def call(id:, prefix: "Hey")
    user = User.find(id)

    "#{prefix} #{user.name} !"
  end
end

# app/tools/users_create_tool.rb
# frozen_string_literal: true

class UsersCreateTool < ApplicationTool
  description "Create a user"

  arguments do
    required(:name).filled(:string).description("Name of the user")
    required(:email).filled(:string).description("Email of the user")
    required(:age).filled(:integer).description("Age of the user")
  end

  def call(name:, email:, age:)
    user = User.create!(name: name, email: email, age: age)

    "User created: #{user.inspect}"
  end
end

# config/initializers/fast_mcp.rb
# frozen_string_literal: true

# FastMcp - Model Context Protocol for Rails
# This initializer sets up the MCP middleware in your Rails application.
#
# In Rails applications, you can use:
# - ActionTool::Base as an alias for FastMcp::Tool
# - ActionResource::Base as an alias for FastMcp::Resource
#
# All your tools should inherit from ApplicationTool which already uses ActionTool::Base,
# and all your resources should inherit from ApplicationResource which uses ActionResource::Base.

# Mount the MCP middleware in your Rails application
# You can customize the options below to fit your needs.
require "fast_mcp"

FastMcp.mount_in_rails(
  Rails.application,
  name: Rails.application.class.module_parent_name.underscore.dasherize,
  version: "1.0.0",
  path_prefix: "/mcp", # This is the default path prefix
  messages_route: "messages", # This is the default route for the messages endpoint
  sse_route: "sse", # This is the default route for the SSE endpoint
  # Add allowed origins below, it defaults to Rails.application.config.hosts
  allowed_origins: [ "localhost", "127.0.0.1", "[::1]", "b69340af24ec.ngrok-free.app", /.*\.example\.com/ ],
  localhost_only: false, # Set to false to allow connections from other hosts
  # whitelist specific ips to if you want to run on localhost and allow connections from other IPs
  # allowed_ips: ['127.0.0.1', '::1']
  # authenticate: true,       # Uncomment to enable authentication
  # auth_token: 'your-token', # Required if authenticate: true
) do |server|
  Rails.application.config.after_initialize do
    # FastMcp will automatically discover and register:
    # - All classes that inherit from ApplicationTool (which uses ActionTool::Base)
    # - All classes that inherit from ApplicationResource (which uses ActionResource::Base)
    server.register_tools(*ApplicationTool.descendants)
    server.register_resources(*ApplicationResource.descendants)
    # alternatively, you can register tools and resources manually:
    # server.register_tool(MyTool)
    # server.register_resource(MyResource)
  end
end