pretty good

1 files changed, 44 insertions, 16 deletions

diff --git a/go.sh b/go.sh
index 7d678bc..23d06d0 100755
--- a/go.sh
+++ b/go.sh
@@ -1,4 +1,5 @@
 #!/bin/bash
+MAX_AGE_SECONDS=60
 
 read_config()
 {
@@ -7,7 +8,7 @@ read_config()
 
 check_dependencies()
 {
-        for c in flock jq btrfs pv mv
+        for c in flock jq btrfs pv realpath stat date mv ln rm
         do
                 command -v $c >/dev/null
         done
@@ -23,43 +24,70 @@ is_subvolume()
         btrfs subvolume show -- "$1" >/dev/null 2>&1
 }
 
+get_age()
+{
+        now=$(date +%s)
+        then=$(stat -L -c %Y "$1")
+        echo $((now - then))
+}
+
+remove_old_link()
+{
+        if [ -L "$1" ] && [ "$(get_age "$1")" -gt "$2" ]
+        then
+                rm -- "$1"
+        fi
+}
+
 set -e
 check_dependencies
 check_user_is_root
 
-if [ $# != 1 ]
+if [ $# = 1 ]
 then
+        config_file=$1
+else
         echo "Usage: $0 <config.json>" >&2
         exit 1
 fi
 
-[ -r "$1" ]
-exec 3<>"$1"
+[ -r "$config_file" ]
+exec 3<>"$config_file"
 flock -n 3
 declare -A config
 read_config <&3
 
 src=${config[source]}
 dst=${config[destination]}
-head=${config[head]}
-new_snapshot=${src%/}/.snapshot~$(date -Ins)
+remote_head=${config[head]}
 
 is_subvolume "$src"
-if [ "$head" ]
+local_head_link=${src%/}/.snapshot~HEAD
+
+remove_old_link "$local_head_link" "$MAX_AGE_SECONDS"
+
+if [ -e "$local_head_link" ]
 then
-        is_subvolume "$head"
+        local_head=$(realpath -e "$local_head_link")
+else
+        new_snapshot=${src%/}/.snapshot~$(date -Ins)
+        btrfs subvolume snapshot -r -- "$src" "$new_snapshot"
+        # We don't need to create this link at all.
+        ln -rs -T "$new_snapshot" "$local_head_link"
+        local_head=$new_snapshot
 fi
-mkdir -p "$dst"
 
-btrfs subvolume snapshot -r "$src" "$new_snapshot"
-btrfs send "$new_snapshot" ${head:+ -p "$head"} | pv | btrfs receive "$dst"
-jq --arg h "$head" '. | .head=$h' <"$1" >."$1"~tmp
-mv -T -- ."$1"~tmp "$1"
+is_subvolume "$local_head"
 
-#printf "%s\n" "$new_snapshot" > "$head"~tmp
-#mv -T -- "$head"~tmp "$head"
+if [ "${local_head##*/}" = "${remote_head##*/}" ]
+then
+        echo "Up-to-date." >&2
+        exit
+fi
 
-# parent of $src on $dst is $parent
+btrfs send ${remote_head:+ -p "$remote_head"} -- "$local_head" | pv | btrfs receive -- "$dst"
+jq --arg h "$local_head" '. | .head=$h' <"$config_file" >."$config_file"~tmp
+mv -T -- ."$config_file"~tmp "$config_file"
 
 ### OK, basic idea:
 #