UX: redesign admin permalinks page (#29634)

Redesign the permalinks page to follow the UX guide. In addition, the ability to edit permalinks was added.

This change includes:
- move to RestModel
- added Validations
- update endpoint and clear old values after the update
- system specs and improvements for unit tests

app/models/permalink.rb

@@ -1,16 +1,31 @@
 # frozen_string_literal: true
 
 class Permalink < ActiveRecord::Base
+  attr_accessor :permalink_type, :permalink_type_value
+
   belongs_to :topic
   belongs_to :post
   belongs_to :category
   belongs_to :tag
   belongs_to :user
 
+  before_validation :clear_associations
   before_validation :normalize_url, :encode_url
+  before_validation :set_association_value
 
   validates :url, uniqueness: true
 
+  validates :topic_id, presence: true, if: Proc.new { |permalink| permalink.topic_type? }
+  validates :post_id, presence: true, if: Proc.new { |permalink| permalink.post_type? }
+  validates :category_id, presence: true, if: Proc.new { |permalink| permalink.category_type? }
+  validates :tag_id, presence: true, if: Proc.new { |permalink| permalink.tag_type? }
+  validates :user_id, presence: true, if: Proc.new { |permalink| permalink.user_type? }
+  validates :external_url, presence: true, if: Proc.new { |permalink| permalink.external_url_type? }
+
+  %i[topic post category tag user external_url].each do |association|
+    define_method("#{association}_type?") { self.permalink_type == association.to_s }
+  end
+
   class Normalizer
     attr_reader :source
 
@@ -98,6 +113,24 @@ class Permalink < ActiveRecord::Base
   def relative_external_url
     external_url.match?(%r{\A/[^/]}) ? "#{Discourse.base_path}#{external_url}" : external_url
   end
+
+  def clear_associations
+    self.topic_id = nil
+    self.post_id = nil
+    self.category_id = nil
+    self.user_id = nil
+    self.tag_id = nil
+    self.external_url = nil
+  end
+
+  def set_association_value
+    self.topic_id = self.permalink_type_value if self.topic_type?
+    self.post_id = self.permalink_type_value if self.post_type?
+    self.user_id = self.permalink_type_value if self.user_type?
+    self.category_id = self.permalink_type_value if self.category_type?
+    self.external_url = self.permalink_type_value if self.external_url_type?
+    self.tag_id = Tag.where(name: self.permalink_type_value).first&.id if self.tag_type?
+  end
 end
 
 # == Schema Information