make state update atomic and clean up some code

8 files changed, 77 insertions, 14 deletions

diff --git a/core/config b/core/config
index 34c96b8..aedd4f3 100644
--- a/core/config
+++ b/core/config
@@ -1,4 +1,5 @@
 #!/bin/sh
+
 # initialize default configuration values
 export POMODORO_STATE_PATH="${POMODORO_STATE_PATH:-$XDG_CACHE_HOME/$progname}" # ~/.cache/dppt
 export POMODORO_NORMAL_DURATION="${POMODORO_NORMAL_DURATION:-$(( 25 * 60 ))}" # 25 minutes
@@ -6,3 +7,4 @@ export POMODORO_BREAK_SHORT_DURATION="${POMODORO_BREAK_SHORT_DURATION:-$(( 5 * 6
 export POMODORO_BREAK_LONG_DURATION="${POMODORO_BREAK_LONG_DURATION:-$(( 15 * 60 ))}" # 15 minutes
 export POMODORO_BREAK_SHORT_INTERVAL="${POMODORO_BREAK_INTERVAL:-2}" # every other lap
 export POMODORO_BREAK_LONG_INTERVAL="${POMODORO_BREAK_INTERVAL:-6}" # every 3rd break
+
diff --git a/core/help b/core/help
index 98abd1e..4bc5496 100755
--- a/core/help
+++ b/core/help
@@ -1,5 +1,5 @@
 #!/bin/sh
-[ "$1" = "info" ] && echo "show this very message" && exit 2
+[ "$1" = "info" ] && echo "show help" && exit 2
 
 cat << EOF
 $progname -- daemonless posix pomodoro timer
@@ -35,3 +35,4 @@ cat << EOF
 
 if no action is provided, the \`state\` action is chosen by default
 EOF
+
diff --git a/core/lib b/core/lib
index 9892663..21c64f9 100644
--- a/core/lib
+++ b/core/lib
@@ -16,3 +16,22 @@ err() {
 # debug:
 # bc() { tee /dev/stderr | /usr/bin/bc ; }
 
+fmt_time() {
+	ss="$(echo "$1 / 1" | bc)"
+	mm="$(echo "$ss / 60" | bc)"
+	ss="$(echo "$ss % 60" | bc)"
+	hh="$(echo "$mm / 60" | bc)"
+	mm="$(echo "$mm % 60" | bc)"
+	_time_fmt
+}
+
+_time_fmt() { # [HH:]MM:SS
+	[ $hh -gt 0 ] && printf '%02d:' $hh
+	printf "%02d:%02d\n" $mm $ss
+}
+
+# _time_fmt() { # [HHh]MMmSSs
+# 	[ $hh -gt 0 ] && printf '%02dh' $hh
+# 	printf "%02dm%02ds\n" $mm $ss
+# }
+
diff --git a/core/pause b/core/pause
index a55bd30..3037c1c 100755
--- a/core/pause
+++ b/core/pause
@@ -6,7 +6,7 @@
 
 [ "$state" != 'running' ] && err "timer is not running"
 
-time="$("$time - $now" | bc)"
+time="$(echo "$time - $now" | bc)"
 state='paused'
 
 save_state
diff --git a/core/reset b/core/reset
index 5492dce..a4c245e 100755
--- a/core/reset
+++ b/core/reset
@@ -1,5 +1,11 @@
 #!/bin/sh
 [ "$1" = "info" ] && echo "reset the timer and lap counter" && exit 2
 
-rm -rf "$POMODORO_STATE_PATH"
+lap=0
+state='reset'
+update_time=1
+
+. "$core_path/update"
+
+save_state
 
diff --git a/core/start b/core/start
index ae471ad..dbbabc0 100755
--- a/core/start
+++ b/core/start
@@ -28,8 +28,8 @@ done
 
 if [ "$state" = 'running' ] ; then
 	[ $allow_skip -eq 0 ] && err "timer is already running, use -s to skip lap"
-	time="0.0"
 	lap=$(( $lap + 1 ))
+	update_time=1
 	. "$core_path/update"
 fi
 
@@ -37,3 +37,4 @@ time="$(echo "$now + $time" | bc)"
 state='running'
 
 save_state
+
diff --git a/core/state b/core/state
index fcf327d..580afc6 100755
--- a/core/state
+++ b/core/state
@@ -17,5 +17,5 @@ EOF
 }
 
 . "$core_path/update"
-echo "[$state] $lap: ${remaining}s"
+echo "lap $lap, $state, $(fmt_time $remaining)"
 
diff --git a/core/update b/core/update
index 04fd29c..fbe0e86 100644
--- a/core/update
+++ b/core/update
@@ -1,13 +1,12 @@
 #!/bin/sh
 export now="$(date +%s.%N)"
 
-update_time=0
-
+# load current state
 mkdir -p "$POMODORO_STATE_PATH"
 load_or_init() {
 	property="$1"
 	default_value="$2"
-	property_path="$POMODORO_STATE_PATH/$property"
+	property_path="$POMODORO_STATE_PATH/current/$property"
 	if [ -f "$property_path" ] ; then
 		eval $property='"$(cat "$property_path")"'
 	else
@@ -17,7 +16,13 @@ load_or_init() {
 [ -z "$lap" ] && load_or_init lap 0
 [ -z "$state" ] && load_or_init state 'reset'
 [ -z "$time" ] && load_or_init time 0.0
-[ "$time" = "0.0" ] && update_time=1
+
+# save state (for diff)
+diff_state() { printf '%s:' "$lap" "$state" "$time" ; }
+original_state="$(diff_state)"
+
+# allow overriding this value manually
+[ -z "$update_time" ] && update_time=0
 
 # calculate remaining time on timer
 if [ -z "$remaining" ] ; then
@@ -34,6 +39,7 @@ fi
 
 # update remaining time if in reset
 [ "$state" = 'reset' ] && update_time=1
+[ "$time" = "0.0" ] && update_time=1
 
 if [ $update_time -eq 1 ] ; then
 	time="$POMODORO_NORMAL_DURATION"
@@ -42,12 +48,40 @@ if [ $update_time -eq 1 ] ; then
 	remaining="$time"
 fi
 
-# save state
 save_state() {
-	mkdir -p "$POMODORO_STATE_PATH"
-	echo "$lap" > "$POMODORO_STATE_PATH/lap"
-	echo "$state" > "$POMODORO_STATE_PATH/state"
-	echo "$time" > "$POMODORO_STATE_PATH/time"
+	# do not save files if state didn't change
+	[ "$original_state" = "$(diff_state)" ] && return
+
+	# The state update needs to be atomic since other instances may access the
+	# state during an update. This is accomplished by replacing a single symlink,
+	# which should be atomic on most POSIX-compatible platforms, and is less
+	# complicated than a lockfile. $POMODORO_STATE_PATH contains three items:
+	#
+	# 1. current -- a symlink to `primary` or `secondary`
+	# 2. primary -- folder containing current state*
+	# 3. secondary -- temporary folder used write new state
+	#
+	# * `primary` will only contain stale state during an update (i.e. while
+	# `current` is pointing to `secondary`)
+
+	mkdir -p "$POMODORO_STATE_PATH/primary" "$POMODORO_STATE_PATH/secondary"
+
+	echo "$lap" > "$POMODORO_STATE_PATH/secondary/lap"
+	echo "$state" > "$POMODORO_STATE_PATH/secondary/state"
+	echo "$time" > "$POMODORO_STATE_PATH/secondary/time"
+
+	ln -sf "secondary" "$POMODORO_STATE_PATH/secondary/current"
+
+	# this is the atomic update that replaces the `current` symlink with the new
+	# state
+	mv "$POMODORO_STATE_PATH/secondary/current" "$POMODORO_STATE_PATH"
+
+	# next, replace the old `primary` state with the new state from `secondary`,
+	# and update the symlink a second time to now point to `primary` again (this
+	# does not change the state)
+	cp -r "$POMODORO_STATE_PATH/secondary/." "$POMODORO_STATE_PATH/primary/"
+	ln -sf "primary" "$POMODORO_STATE_PATH/primary/current"
+	mv "$POMODORO_STATE_PATH/primary/current" "$POMODORO_STATE_PATH"
 }
 
 # export state variables