build.sh: find d8, apktool and apksigner in ~/android-toolchain/calendar-tools, and a JDK, by default

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

build.sh

@@ -11,7 +11,17 @@
 set -eu
 cd "$(dirname "$0")"
 OUT=build
+# defaults: the copies in ~/android-toolchain/calendar-tools (build-tools 34's d8.jar and apksigner.jar, apktool 2.9.3)
+CT=${CALENDAR_TOOLS:-$HOME/android-toolchain/calendar-tools}
+if [ -z "${D8:-}" ] && [ -f "$CT/d8.jar" ]; then D8="java -cp $CT/d8.jar com.android.tools.r8.D8"; fi
 D8=${D8:-d8}
+if [ -z "${APKTOOL:-}" ] && [ -f "$CT/apktool_2.9.3.jar" ]; then APKTOOL=$CT/apktool_2.9.3.jar; fi
+if [ -z "${APKSIGNER:-}" ] && [ -f "$CT/apksigner.jar" ]; then APKSIGNER=$CT/apksigner.jar; fi
+if ! command -v javac >/dev/null 2>&1; then
+  for j in "${JAVA_HOME:-}" /opt/homebrew/opt/openjdk@17 /opt/homebrew/opt/openjdk; do
+    if [ -n "$j" ] && [ -x "$j/bin/javac" ]; then JAVA_HOME=$j; PATH=$j/bin:$PATH; export JAVA_HOME PATH; break; fi
+  done
+fi
 APKTOOL=${APKTOOL:?set APKTOOL=/path/to/apktool.jar}
 APKSIGNER=${APKSIGNER:?set APKSIGNER=/path/to/apksigner.jar}
 KS=${KEYSTORE:-gingercal.keystore}