From f6f16b8e3ee34ba2ca1faa2622cbcf545b753c0f Mon Sep 17 00:00:00 2001
From: Andrea Amantini <lo.zampino@gmail.com>
Date: Fri, 16 Aug 2024 11:44:34 +0200
Subject: [PATCH] Support strikethrough syntax

---
 deps.edn                                 | 1 +
 src/nextjournal/markdown/parser/impl.clj | 9 +++++++--
 test/nextjournal/markdown_test.cljc      | 9 +++++++++
 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/deps.edn b/deps.edn
index 97a6e3e..09186b6 100644
--- a/deps.edn
+++ b/deps.edn
@@ -12,6 +12,7 @@
         com.github.commonmark/commonmark-java {:mvn/version "faea2a2a61cfa1b1f26a4e914532b651b3602e34"}
         com.github.commonmark.commonmark-java/commonmark-ext-task-list-items {:mvn/version "faea2a2a61cfa1b1f26a4e914532b651b3602e34"}
         com.github.commonmark.commonmark-java/commonmark-ext-gfm-tables {:mvn/version "faea2a2a61cfa1b1f26a4e914532b651b3602e34"}
+        com.github.commonmark.commonmark-java/commonmark-ext-gfm-strikethrough {:mvn/version "faea2a2a61cfa1b1f26a4e914532b651b3602e34"}
 
         ;; jitpack bisect
 
diff --git a/src/nextjournal/markdown/parser/impl.clj b/src/nextjournal/markdown/parser/impl.clj
index 51daef0..a2b9bab 100644
--- a/src/nextjournal/markdown/parser/impl.clj
+++ b/src/nextjournal/markdown/parser/impl.clj
@@ -3,9 +3,10 @@
             [nextjournal.markdown.parser.impl.types]
             [nextjournal.markdown.parser.impl.formulas :as formulas]
             [nextjournal.markdown.parser.impl.utils :as u])
-  (:import (org.commonmark.parser Parser)
+  (:import (org.commonmark.ext.gfm.tables TableBlock TableBody TableRow TableHead TableCell TablesExtension)
+           (org.commonmark.ext.gfm.strikethrough Strikethrough StrikethroughExtension)
            (org.commonmark.ext.task.list.items TaskListItemsExtension TaskListItemMarker)
-           (org.commonmark.ext.gfm.tables TableBlock TableBody TableRow TableHead TableCell TablesExtension)
+           (org.commonmark.parser Parser)
    #_(org.commonmark.ext.footnotes FootnotesExtension FootnoteReference FootnoteDefinition InlineFootnote)
            (org.commonmark.node Node AbstractVisitor
                                 Document
@@ -57,6 +58,7 @@
       (extensions [(formulas/extension)
                    (TaskListItemsExtension/create)
                    (TablesExtension/create)
+                   (StrikethroughExtension/create)
                    #_(.. (FootnotesExtension/builder)
                          (inlineFootnotes true)
                          (build))])
@@ -144,6 +146,9 @@
                                                          :content [{:type :text
                                                                     :text (.getLiteral node)}]}) z/down z/rightmost))))
 
+(defmethod open-node Strikethrough [ctx _node]
+  (update-current ctx (fn [loc] (-> loc (z/append-child {:type :strikethrough :content []}) z/down z/rightmost))))
+
 (defmethod open-node Link [ctx ^Link node]
   (update-current ctx (fn [loc]
                         (-> loc (z/append-child {:type :link
diff --git a/test/nextjournal/markdown_test.cljc b/test/nextjournal/markdown_test.cljc
index 628eaf2..c637ab3 100644
--- a/test/nextjournal/markdown_test.cljc
+++ b/test/nextjournal/markdown_test.cljc
@@ -188,6 +188,15 @@ $$\\int_a^bf(t)dt$$
              "two"]]]]
          (md/->hiccup markdown-text))))
 
+(deftest strikethrough-test
+  (testing "single tilde")
+  ;; Here markdown-it follows Pandoc and uses single ~ for 'sub' (enabled by default https://github.com/markdown-it/markdown-it/tree/master?tab=readme-ov-file#syntax-extensions).
+  ;; It differs from GFM spec https://github.github.com/gfm/#strikethrough-extension- which allows signle tilde syntax
+  (testing "double tilde"
+    (is (= {:type :paragraph, :content [{:type :text, :text "some "} {:type :strikethrough, :content [{:type :text, :text "not ok"}]} {:type :text, :text " text"}]}
+           (-> (md/parse "some ~~not ok~~ text")
+               :content first)))))
+
 (deftest tables-test
   (is (= {:type :doc
           :content [{:type :table