From a0a120b31e467d6741d94e1eb4a2e7603e31ce71 Mon Sep 17 00:00:00 2001
From: David Eisinger <david.eisinger@gmail.com>
Date: Wed, 8 Apr 2026 23:54:20 -0400
Subject: [PATCH] Cache dither results

---
 .gitea/workflows/deploy.yaml |  1 +
 .gitignore                   |  1 +
 bin/build                    |  5 ++++-
 bin/dither/dither.rb         | 37 +++++++++++++++++++++++++++++++++++-
 bin/server                   |  5 ++++-
 5 files changed, 46 insertions(+), 3 deletions(-)

diff --git a/.gitea/workflows/deploy.yaml b/.gitea/workflows/deploy.yaml
index 758d806..b995cb2 100644
--- a/.gitea/workflows/deploy.yaml
+++ b/.gitea/workflows/deploy.yaml
@@ -9,6 +9,7 @@ on:
 env:
   HUGO_VERSION: 0.160.1
   DEPLOY_DIR: /var/www/davideisinger.com
+  DITHER_CACHE_DIR: /workspace-cache/dither
 
 jobs:
   deploy:
diff --git a/.gitignore b/.gitignore
index 2aa9e03..04c63ff 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 .hugo_build.lock
+.cache
 public
 resources/_gen
 secret.key
diff --git a/bin/build b/bin/build
index 933cd57..9836aa5 100755
--- a/bin/build
+++ b/bin/build
@@ -3,10 +3,13 @@ set -euo pipefail
 
 repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
 dither_dir="${repo_root}/bin/dither"
+cache_dir="${DITHER_CACHE_DIR:-${repo_root}/.cache/dither}"
+
+mkdir -p "${cache_dir}"
 
 pushd "${dither_dir}" >/dev/null
 bundle install
-ROOT="${repo_root}/content" KEY="${repo_root}/secret.key" bundle exec rackup -p 4567 &
+ROOT="${repo_root}/content" KEY="${repo_root}/secret.key" DITHER_CACHE_DIR="${cache_dir}" bundle exec rackup -p 4567 &
 dither_pid=$!
 popd >/dev/null
 
diff --git a/bin/dither/dither.rb b/bin/dither/dither.rb
index 1a9284f..7bf7938 100644
--- a/bin/dither/dither.rb
+++ b/bin/dither/dither.rb
@@ -1,5 +1,7 @@
 require "sinatra"
 require "mini_magick"
+require "digest"
+require "fileutils"
 require "tempfile"
 
 MiniMagick.logger.level = Logger::DEBUG
@@ -8,6 +10,26 @@ ROOT = ENV.fetch("ROOT")
 KEY = ENV.fetch("KEY")
 DITHER = ENV["DITHER"] != "0"
 FORMAT = "png"
+CACHE_DIR = ENV["DITHER_CACHE_DIR"]
+
+def cache_path_for(path, geometry)
+  return unless CACHE_DIR
+
+  source_path = "#{ROOT}/#{path}.enc"
+  stat = File.stat(source_path)
+  cache_key = Digest::SHA256.hexdigest([
+    path,
+    stat.size,
+    stat.mtime.to_f,
+    geometry,
+    DITHER,
+    FORMAT,
+    1
+  ].join("\0"))
+
+  FileUtils.mkdir_p(CACHE_DIR)
+  File.join(CACHE_DIR, "#{cache_key}.#{FORMAT}")
+end
 
 get "/*" do |path|
   halt 404, {"Content-Type" => "text/plain"}, "not found" unless File.exist?("#{ROOT}/#{path}.enc")
@@ -17,6 +39,11 @@ get "/*" do |path|
   geometry = params["geo"] unless params["geo"] == ""
   geometry.gsub!(/\d+/) { |n| n.to_i * 2 } if geometry && !DITHER
 
+  cached_path = cache_path_for(path, geometry)
+  if cached_path && File.exist?(cached_path)
+    return File.binread(cached_path)
+  end
+
   decrypted = Tempfile.new(["dither", File.extname(path)])
   decrypted.binmode
   decrypted.close
@@ -59,7 +86,15 @@ get "/*" do |path|
     end
 
     convert << "#{FORMAT.upcase}:-"
-    convert.call
+    output = convert.call
+
+    if cached_path
+      temp_cache_path = "#{cached_path}.tmp-#{Process.pid}"
+      File.binwrite(temp_cache_path, output)
+      FileUtils.mv(temp_cache_path, cached_path)
+    end
+
+    output
   ensure
     decrypted.unlink
   end
diff --git a/bin/server b/bin/server
index 455453d..c5aa453 100755
--- a/bin/server
+++ b/bin/server
@@ -3,9 +3,12 @@ set -euo pipefail
 
 repo_root=$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)
 dither_dir="${repo_root}/bin/dither"
+cache_dir="${DITHER_CACHE_DIR:-${repo_root}/.cache/dither}"
+
+mkdir -p "${cache_dir}"
 
 pushd "${dither_dir}" >/dev/null
-ROOT="${repo_root}/content" KEY="${repo_root}/secret.key" bundle exec ruby dither.rb &
+ROOT="${repo_root}/content" KEY="${repo_root}/secret.key" DITHER_CACHE_DIR="${cache_dir}" bundle exec ruby dither.rb &
 dither_pid=$!
 popd >/dev/null