Add cache_decision + tests

Implements cache_decision <cat> <prog> <version> which inspects
$PKG_CACHE/<cat>/<prog>/ and returns "cached", "bump:OLD:NEW", or "new".
Empty PKG_CACHE disables the cache. Tests in test-logic.sh cover all
four outcomes and are driven pure (no VM needed).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

2 files changed, 55 insertions, 0 deletions

diff --git a/sbo-batch-test b/sbo-batch-test
index a9e3d14..1e0020c 100755
--- a/sbo-batch-test
+++ b/sbo-batch-test
@@ -307,6 +307,42 @@ update_base() {
 }
 
 # =============================================================================
+# Package cache. Persistent, on-disk store of built packages so unchanged deps
+# are installed from cache instead of rebuilt. Layout mirrors the SBo tree:
+#   $PKG_CACHE/<cat>/<prog>/<prog>-<ver>-<arch>-<build>_<tag>.txz
+# One .txz per prog dir (the latest tested build). Key is prog+version; build
+# number, arch, and tag do not affect a hit. Empty PKG_CACHE disables caching.
+# =============================================================================
+
+# Echo the version field of a cached package filename. <file> is a basename like
+# prog-1.2-x86_64-1_danix.txz; prog may itself contain dashes, so strip the known
+# prog prefix first, then take the field up to the next dash.
+_cache_ver_of() {
+  local prog="$1" base="$2"
+  base="${base#"$prog"-}"     # drop "prog-"
+  echo "${base%%-*}"          # version is up to the next dash
+}
+
+# cache_decision <cat> <prog> <version> -> echoes: cached | bump:OLD:NEW | new
+cache_decision() {
+  local cat="$1" prog="$2" version="$3"
+  [[ -z "$PKG_CACHE" ]] && { echo new; return; }
+  local dir="$PKG_CACHE/$cat/$prog"
+  local f newest=""
+  for f in "$dir/$prog"-*.t?z; do
+    [[ -e "$f" ]] || continue
+    [[ -z "$newest" || "$f" -nt "$newest" ]] && newest="$f"
+  done
+  [[ -z "$newest" ]] && { echo new; return; }
+  local have; have="$(_cache_ver_of "$prog" "$(basename "$newest")")"
+  if [[ "$have" == "$version" ]]; then
+    echo cached
+  else
+    echo "bump:$have:$version"
+  fi
+}
+
+# =============================================================================
 # SBo tree lookup. Find the SlackBuild dir for a prog name across roots.
 # Echoes the dir path, returns 0 if found, 1 otherwise.
 # =============================================================================
diff --git a/test-logic.sh b/test-logic.sh
index 13d97f8..7575ea7 100755
--- a/test-logic.sh
+++ b/test-logic.sh
@@ -104,6 +104,25 @@ else
   bad "cascade dead: b=${blocked[b]:-0} a=${blocked[a]:-0}"
 fi
 
+# --- package cache ----------------------------------------------------------
+PKG_CACHE=$(mktemp -d)
+mkc() { mkdir -p "$PKG_CACHE/$1/$2"; : > "$PKG_CACHE/$1/$2/$3"; }
+
+# exact version match -> cached
+mkc net libfoo "libfoo-1.1-x86_64-1_danix.txz"
+[[ "$(cache_decision net libfoo 1.1)" == "cached" ]] && ok "cache hit on version match" || bad "cache_decision should be cached, got [$(cache_decision net libfoo 1.1)]"
+
+# different version cached -> bump:old:new
+[[ "$(cache_decision net libfoo 1.2)" == "bump:1.1:1.2" ]] && ok "cache bump reported" || bad "cache_decision bump wrong, got [$(cache_decision net libfoo 1.2)]"
+
+# nothing cached -> new
+[[ "$(cache_decision net libbar 1.0)" == "new" ]] && ok "cache new for absent prog" || bad "cache_decision should be new, got [$(cache_decision net libbar 1.0)]"
+
+# empty PKG_CACHE disables -> new
+PKG_CACHE_SAVE="$PKG_CACHE"; PKG_CACHE=""
+[[ "$(cache_decision net libfoo 1.1)" == "new" ]] && ok "empty PKG_CACHE disables (new)" || bad "disabled cache should be new, got [$(cache_decision net libfoo 1.1)]"
+PKG_CACHE="$PKG_CACHE_SAVE"
+
 # --- result -----------------------------------------------------------------
 echo
 echo "$pass passed, $fail failed"