dtext links: add table for tracking links between wikis.

Add a dtext_links table for tracking links between wiki pages. This is
to allow for broken link detection and "what links here" searches, among
other uses.

test/unit/d_text_test.rb

@@ -56,5 +56,31 @@ class DTextTest < ActiveSupport::TestCase
         refute_match(/dtext-tag-does-not-exist/, DText.format_text("[[help:nothing]]"))
       end
     end
+
+    context "#parse_wiki_titles" do
+      should "parse wiki links in dtext" do
+        assert_equal(["foo"], DText.parse_wiki_titles("[[foo]] [[FOO]"))
+      end
+    end
+
+    context "#parse_external_links" do
+      should "parse external links in dtext" do
+        dtext = <<~EOS
+          * https://test1.com
+          * <https://test2.com>
+          * "test":https://test3.com
+          * "test":[https://test4.com]
+          * [https://test5.com](test)
+          * <a href="https://test6.com">test</a>
+        EOS
+
+        links = %w[
+          https://test1.com https://test2.com https://test3.com
+          https://test4.com https://test5.com https://test6.com
+        ]
+
+        assert_equal(links, DText.parse_external_links(dtext))
+      end
+    end
   end
 end

test/unit/wiki_page_test.rb

@@ -110,6 +110,21 @@ class WikiPageTest < ActiveSupport::TestCase
         version = WikiPageVersion.last
         assert_not_equal(@wiki_page.creator_id, version.updater_id)
       end
+
+      should "update its dtext links" do
+        @wiki_page.update!(body: "[[long hair]]")
+        assert_equal(1, @wiki_page.dtext_links.size)
+        assert_equal("wiki_link", @wiki_page.dtext_links.first.link_type)
+        assert_equal("long_hair", @wiki_page.dtext_links.first.link_target)
+
+        @wiki_page.update!(body: "http://www.google.com")
+        assert_equal(1, @wiki_page.dtext_links.size)
+        assert_equal("external_link", @wiki_page.dtext_links.first.link_type)
+        assert_equal("http://www.google.com", @wiki_page.dtext_links.first.link_target)
+
+        @wiki_page.update!(body: "nothing")
+        assert_equal(0, @wiki_page.dtext_links.size)
+      end
     end
   end
 end