Add basic functionality

app/controllers/application_controller.rb

@@ -1,2 +1,5 @@
 class ApplicationController < ActionController::Base
+  def resource_class
+    controller_path.classify.constantize
+  end
 end

app/controllers/countries_controller.rb

@@ -0,0 +1,13 @@
+class CountriesController < ApplicationController
+  helper_method %i[countries country]
+
+  def countries
+    resource_class.all
+  end
+
+  def country
+    return resource_class.find(params[:id]) if params[:id].is_a?(Integer)
+    return resource_class.find_by(iso2: params[:id]) if params[:id].length == 2
+    resource_class.find_by(iso3: params[:id])
+  end
+end

app/controllers/people_controller.rb

@@ -0,0 +1,7 @@
+class PeopleController < ApplicationController
+  helper_method :person
+
+  def person
+    resource_class.find(params[:id])
+  end
+end

app/models/admission.rb

@@ -1,4 +1,24 @@
 class Admission < ApplicationRecord
-  belongs_to :country
-  belongs_to :person
+  belongs_to :country, inverse_of: :admissions
+  belongs_to :person, inverse_of: :admissions
+  belongs_to :previous, class_name: name, inverse_of: :next, optional: true
+  has_one :next, class_name: name, foreign_key: :previous_id, inverse_of: :previous
+
+  scope :ordered, -> { order(:arrived_on, :previous_id) }
+  scope :before, -> (date) { where("#{table_name}.arrived_on <= ?", date) }
+  scope :after, -> (date) { where("#{table_name}.arrived_on >= ?", date) }
+  
+  around_create :set_previous
+  before_destroy :update_nexts_previous
+
+  def set_previous
+    self.previous ||= person.admissions.ordered.before(arrived_on).last
+    future_next = previous&.reload_next
+    yield
+    future_next&.update(previous: self)
+  end
+
+  def update_nexts_previous
+    self.next&.update(previous: previous)
+  end
 end

app/models/country.rb

@@ -1,2 +1,4 @@
 class Country < ApplicationRecord
+  has_many :admissions, inverse_of: :country
+  has_many :people, foreign_key: :birth_country_id, inverse_of: :birth_country
 end

app/models/person.rb

@@ -1,2 +1,18 @@
 class Person < ApplicationRecord
+  belongs_to :birth_country, class_name: Country.name
+  has_many :admissions
+
+  def stays
+    stays = []
+    admissions.ordered.includes(:country).all.each_cons(2) do |a, b|
+      stays.push(
+        country: a.country,
+        arrival: a.arrived_on,
+        departure: b.arrived_on,
+        duration: (b.arrived_on - a.arrived_on).to_i + 1
+      )
+    end
+
+    stays
+  end
 end

app/views/countries/index.html.slim

@@ -0,0 +1,11 @@
+h1 Countries
+table
+  tr
+    th Name
+    th ISO 3166-1 alpha-2 code
+    th ISO 3166-1 alpha-3 code
+  - for country in countries
+    tr
+      td = country.name
+      td = country.iso2
+      td = country.iso3

app/views/countries/show.html.slim

@@ -0,0 +1,9 @@
+h1 = country.name
+b ID &nbsp
+= country.id
+br
+b ISO 3166-1 alpha-2 code &nbsp
+= country.iso2
+br
+b ISO 3166-1 alpha-2 code &nbsp
+= country.iso3

app/views/people/show.html.slim

@@ -0,0 +1,15 @@
+h1= person.name
+table
+  thead
+    tr
+      th Country
+      th Arrival
+      th Departure
+      th Duration (days)
+  tbody
+    - for stay in person.stays
+      tr
+        td = stay[:country].name + " (" + stay[:country].iso2 + ")" 
+        td = stay[:arrival]
+        td = stay[:departure]
+        td = stay[:duration]