From bdc6cf985ba0fa319d613b8ec874eb032dc04b03 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Sat, 9 May 2020 18:14:43 -0700
Subject: [PATCH] Cache KaTeX return values in Ruby script.

---
 blog/convert.rb | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/blog/convert.rb b/blog/convert.rb
index 4962ee2..697dc2d 100644
--- a/blog/convert.rb
+++ b/blog/convert.rb
@@ -1,33 +1,35 @@
 require "open3"
 require "nokogiri"
 
-def perform_katex_sub(content)
-  rendered = content.gsub /\\\(((?:[^\\]|\\[^\)])*)\\\)/ do |match|
-    puts "  Rendering #{$~[1]}"
-    Open3.popen3("katex") do |i, o, e, t|
-      i.write $~[1]
+def render_cached(cache, command, string, render_comment = nil)
+  cache.fetch(string) do |new|
+    puts "  Rendering #{render_comment || new}"
+    cache[string] = Open3.popen3(command) do |i, o, e, t|
+      i.write new
       i.close
       o.read.force_encoding(Encoding::UTF_8).strip
     end
   end
+end
+
+def perform_katex_sub(inline_cache, display_cache, content)
+  rendered = content.gsub /\\\(((?:[^\\]|\\[^\)])*)\\\)/ do |match|
+    render_cached(inline_cache, "katex", $~[1])
+  end
   rendered = rendered.gsub /\$\$((?:[^\$]|$[^\$])*)\$\$/ do |match|
-    puts "  Rendering display."
-    Open3.popen3("katex -d") do |i, o, e, t|
-      i.write $~[1]
-      i.close
-      o.read.force_encoding(Encoding::UTF_8).strip
-    end
+    render_cached(display_cache, "katex -d", $~[1], "display")
   end
   return rendered
 end
 
 files = ARGV[0..-1]
+inline_cache, display_cache = {}, {}
 
 files.each do |file|
   puts "Rendering file: #{file}"
   document = Nokogiri::HTML.parse(File.open(file))
   document.search('//*[not(self::code)]/text()').each do |t|
-    t.replace(perform_katex_sub(t.content))
+    t.replace(perform_katex_sub(inline_cache, display_cache, t.content))
   end
   File.write(file, document.to_html)
 end