build-pdf: only build changed folders since last commit (#11773)

* build-pdf: only build changed folders since last commit

* build-pdf: only determine language if needed

* build-pdf: refactor the script

scripts/pdf/build-pdf.sh

@@ -7,7 +7,6 @@ set -ex
 function process_page {
   pageDir="$1"
   folder=$(basename "${pageDir}")
-  language="${folder##*.}"
   case $folder in
     pages.bn | pages.ja | pages.ko | pages.ml | pages.ta | pages.th | pages.zh | pages.zh_TW)
       ;;
@@ -15,14 +14,32 @@ function process_page {
       python3 render.py "${pageDir}" -c solarized-light
       ;;
     *)
+      language="${folder##*.}"
       python3 render.py "${pageDir}" -c basic -o "tldr-book-${language}.pdf"
       ;;
   esac
 }
 
 function main {
-  for pageDir in ../../pages*; do
-    process_page "${pageDir}"
+  type="$1"
+  case $type in
+    "all")
+      pageDirs=(../../pages*)
+      ;;
+    *)
+      changedFiles=$(git diff-tree --no-commit-id --name-only -r "$(git rev-parse HEAD)")
+      changedPageDirs=$(echo "$changedFiles" | awk -F/ '/^(pages[^\/]+|pages)\//{print $1}' | sort -u)
+      
+      if [ -z "$changedPageDirs" ]; then
+        pageDirs=()
+      else
+        mapfile -t pageDirs <<< "$changedPageDirs"
+      fi
+      ;;
+  esac
+  
+  for pageDir in "${pageDirs[@]}"; do
+    process_page "../../${pageDir}"
   done
 }
 
@@ -30,4 +47,4 @@ function main {
 # MAIN
 ###################################
 
-main
+main $1