nixos/paperless: Reindex documents after updating to 1.12.x

This causes a reindex of all documents to allow for comments made before
1.12.x to be searchable.

Also change the format of the version file to just include the version,
not the whole store path.
This simplifies version comparisons and causes migrations to run only
when the version has changed.

Co-Authored-By: Martin Weinelt <hexa@darmstadt.ccc.de>

nixos/modules/services/misc/paperless.nix

@@ -226,9 +226,26 @@ in
 
         # Auto-migrate on first run or if the package has changed
         versionFile="${cfg.dataDir}/src-version"
-        if [[ $(cat "$versionFile" 2>/dev/null) != ${pkg} ]]; then
+        version=$(cat "$versionFile" 2>/dev/null || echo 0)
+
+        if [[ $version != ${pkg.version} ]]; then
           ${pkg}/bin/paperless-ngx migrate
-          echo ${pkg} > "$versionFile"
+
+          # Parse old version string format for backwards compatibility
+          version=$(echo "$version" | grep -ohP '[^-]+$')
+
+          versionLessThan() {
+            target=$1
+            [[ $({ echo "$version"; echo "$target"; } | sort -V | head -1) != "$target" ]]
+          }
+
+          if versionLessThan 1.12.0; then
+            # Reindex documents as mentioned in https://github.com/paperless-ngx/paperless-ngx/releases/tag/v1.12.1
+            echo "Reindexing documents, to allow searching old comments. Required after the 1.12.x upgrade."
+            ${pkg}/bin/paperless-ngx document_index reindex
+          fi
+
+          echo ${pkg.version} > "$versionFile"
         fi
       ''
       + optionalString (cfg.passwordFile != null) ''