Run discover-overlay-wait as a user unit and rework the vidthumb cache

vidthumb names thumbnails by a hash of path, size and mtime instead of a jq index that broke on quotes in filenames; systemd-tmpfiles removes ones unused for 30 days. discover-overlay-wait now runs from a systemd user unit started by xmonad and logs to the journal.

.config/systemd/user/discover-overlay-wait.service

@@ -0,0 +1,7 @@
+[Unit]
+Description=Run discover-overlay while Discord is running
+
+[Service]
+ExecStart=%h/.local/bin/discover-overlay-wait
+Restart=on-failure
+RestartSec=5

.config/user-tmpfiles.d/vidthumb.conf

@@ -0,0 +1,2 @@
+# Remove vidthumb thumbnails (and leftover temp files) not used for 30 days; %C is $XDG_CACHE_HOME.
+e %C/vidthumb - - - 30d

.config/xmonad/xmonad.hs

@@ -274,7 +274,7 @@ myStartupHook = do
   spawnOnce "numlockx"
   spawnOnce "blueman-applet"
   spawnOnce "adb start-server"
-  spawnOnce "/home/fuxino/.local/bin/discover-overlay-wait"
+  spawnOnce "systemctl --user start discover-overlay-wait"
 
 -- Manage hook
 myManageHook :: ManageHook

.local/bin/discover-overlay-wait

@@ -1,4 +1,7 @@
 #!/bin/sh
+# Runs discover-overlay while Discord's RPC port is up and stops it when Discord exits.
+# Run by discover-overlay-wait.service (started from xmonad); output goes to the journal.
+
 port_up() {
     ss -ltn | grep -qE '127\.0\.0\.1:64[67][0-9]'
 }
@@ -8,7 +11,7 @@ while true; do
     sleep 5
     port_up || continue   # port vanished again, Discord was still restarting
 
-    discover-overlay >> /tmp/discover-overlay.log 2>&1 &
+    discover-overlay &
     pid=$!
 
     while port_up && kill -0 "$pid" 2>/dev/null; do sleep 3; done

.local/bin/vidthumb

@@ -1,36 +1,29 @@
-#!/usr/bin/env bash
+#!/bin/bash
+# Prints a cached thumbnail for the video in $1 (used by the lf preview), creating it if needed.
+# Thumbnails are named by a hash of path, size and mtime, so a changed file gets a new one.
+# Hits touch the file; systemd-tmpfiles (~/.config/user-tmpfiles.d/vidthumb.conf) removes unused ones.
 
-if ! [ -f "$1" ]; then
-	exit 1
-fi
+[[ -f $1 ]] || exit 1
 
-cache="$HOME/.cache/vidthumb"
-index="$cache/index.json"
-movie="$(realpath "$1")"
+cache="${XDG_CACHE_HOME:-$HOME/.cache}/vidthumb"
+video=$(realpath -- "$1") || exit 1
+stamp=$(stat -c '%s.%Y' -- "$video") || exit 1
+key=$(printf '%s\0%s' "$video" "$stamp" | sha256sum)
+thumb="$cache/${key%% *}.jpg"
 
-mkdir -p "$cache"
-
-if [ -f "$index" ]; then
-	thumbnail="$(jq -r ". \"$movie\"" <"$index")"
-	if [[ "$thumbnail" != "null" ]]; then
-		if [[ ! -f "$cache/$thumbnail" ]]; then
-			exit 1
-		fi
-		echo "$cache/$thumbnail"
+if [[ -s $thumb ]]; then
+    touch -- "$thumb"
+    printf '%s\n' "$thumb"
     exit 0
 fi
-fi
 
-thumbnail="$(uuidgen).jpg"
-
-if ! ffmpegthumbnailer -i "$movie" -o "$cache/$thumbnail" -s 0 2>/dev/null; then
+mkdir -p -- "$cache" || exit 1
+# Write to a temp file first, so an interrupted or concurrent run never leaves a broken thumbnail.
+tmp=$(mktemp --suffix=.jpg "$cache/.tmp.XXXXXX") || exit 1
+if ffmpegthumbnailer -i "$video" -o "$tmp" -s 0 2> /dev/null && [[ -s $tmp ]]; then
+    mv -f -- "$tmp" "$thumb"
+    printf '%s\n' "$thumb"
+else
+    rm -f -- "$tmp"
     exit 1
 fi
-
-if [[ ! -f "$index" ]]; then
-	echo "{\"$movie\": \"$thumbnail\"}" >"$index"
-fi
-json="$(jq -r --arg "$movie" "$thumbnail" ". + {\"$movie\": \"$thumbnail\"}" <"$index")"
-echo "$json" >"$index"
-
-echo "$cache/$thumbnail"