From 1aa20c6cce08345a634ae190ea79ce45866352c1 Mon Sep 17 00:00:00 2001
From: Abigail <abigail@dogbuilt.net>
Date: Tue, 24 Oct 2023 19:04:42 -0400
Subject: [PATCH] Use ghostscript to compress PDF output on RTD

---
 .readthedocs.yaml           |  3 +++
 scripts/rtd-compress-pdf.sh | 24 ++++++++++++++++++++++++
 2 files changed, 27 insertions(+)
 create mode 100755 scripts/rtd-compress-pdf.sh

diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 30ea36d7..e16a7f3f 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -11,6 +11,9 @@ build:
     python: "3.11"
   apt_packages:
     - graphviz
+    - ghostscript
+  jobs:
+    post_build: ./scripts/rtd-compress-pdf.sh
 
 formats:
   - pdf
diff --git a/scripts/rtd-compress-pdf.sh b/scripts/rtd-compress-pdf.sh
new file mode 100755
index 00000000..c7a3c8e8
--- /dev/null
+++ b/scripts/rtd-compress-pdf.sh
@@ -0,0 +1,24 @@
+#!/usr/bin/env sh
+
+# Compresses the PDF output using ghostscript on Read the Docs.
+
+OUTPUT_FILENAME="gm0.pdf"
+DPI=300
+PDF_DIR="$READTHEDOCS_OUTPUT/pdf"
+
+# Check if the PDF build is enabled based on if the PDF output directory exists
+if [ -d "$PDF_DIR" ]; then
+    existing_pdf=$(ls "$PDF_DIR")
+
+    # actually compress the PDF
+    gs -sDEVICE=pdfwrite \
+        -dCompatibilityLevel=1.4 \
+        -dPDFSETTINGS=/ebook \
+        -dNOPAUSE \
+        -dBATCH -dColorImageResolution="$DPI" \
+        -sOutputFile="$PDF_DIR/$OUTPUT_FILENAME" "$PDF_DIR/$existing_pdf"
+
+    # readthedocs expects only one PDF output in the directory
+    # see https://docs.readthedocs.io/en/stable/reference/environment-variables.html#envvar-READTHEDOCS_OUTPUT
+    rm "$PDF_DIR/$existing_pdf"
+fi