#!/bin/sh

# Determine the next wallpaper by round robin from the cloud
# and install it as the background files referenced in
# ~/.config/gnome-settings/misc.ini
#
# Candidates:
#  - Pairs => Both "<name>-d.jpg" and "<name>-l.jpg" exist
#  - Singles => Any other "*.jpg" not following the -d/-l scheme,
#               used as dark and light at the same time
#
# The live `gsettings` URIs point at uniquely named copies
# because `gnome-shell` caches background images by file URI;
# `gnome-restore` cleans up that temporary state during the next login

set -eu



XDG_CONFIG_HOME="${XDG_CONFIG_HOME:-$HOME/.config}"
XDG_DATA_HOME="${XDG_DATA_HOME:-$HOME/.local/share}"
XDG_STATE_HOME="${XDG_STATE_HOME:-$HOME/.local/state}"

SOURCE_DIR="$HOME/Cloud/Null-Tech/Backgrounds"
TARGET_DIR="$XDG_DATA_HOME/backgrounds"

LOCAL_INI="$XDG_CONFIG_HOME/gnome-settings/local/temporary_background.ini"
STATE_FILE="$XDG_STATE_HOME/current-background.txt"



[ -d "$SOURCE_DIR" ] || {
    echo "No such folder: $SOURCE_DIR" >&2
    exit 1
}



# One candidate per line, tab-separated: <dark-file> <light-file>
candidates=$(
    for jpg in "$SOURCE_DIR"/*.jpg; do
        [ -e "$jpg" ] || continue  # because the glob does not expand if empty

        case "$jpg" in

            *-d.jpg)  # Complete pairs only
                stem="${jpg%-d.jpg}"
                [ -f "$stem-l.jpg" ] && printf '%s\t%s\n' "$jpg" "$stem-l.jpg"
                ;;

            *-l.jpg)  # Already handled via its "-d" counterpart above
                ;;

            *)  # A single file to be used for both modes
                printf '%s\t%s\n' "$jpg" "$jpg"
                ;;

        esac
    done
)

if [ -z "$candidates" ]; then
    echo "No usable *.jpg files in: $SOURCE_DIR" >&2
    exit 1
fi

echo "Found $(printf '%s\n' "$candidates" | wc -l) candidate(s)"



# The glob expands alphabetically => "$candidates" is already sorted
# => Pick the first candidate sorting strictly after the last-used one,
#    falling back to the first one if necessary
#    (e.g., for start, wrap-around, or missing state file)
last_background=$(cat "$STATE_FILE" 2>/dev/null || true)
next_background=$(printf '%s\n' "$candidates" | awk -F '\t' -v last_background="$last_background" '$1 > last_background { print; exit }')
[ -n "$next_background" ] || next_background=$(printf '%s\n' "$candidates" | head -n 1)


dark_source=$(printf '%s' "$next_background" | cut -f 1)
light_source=$(printf '%s' "$next_background" | cut -f 2)
echo "Chosen background: $(basename "$dark_source")"



dark_target="$TARGET_DIR/dark.jpg"
light_target="$TARGET_DIR/light.jpg"

# Create a unique name per run
# so that the URIs below never repeat
timestamp=$(date +%s)

dark_live_target="$TARGET_DIR/dark-tmp-$timestamp.jpg"
light_live_target="$TARGET_DIR/light-tmp-$timestamp.jpg"



mkdir -p \
    "$TARGET_DIR" \
    "$(dirname "$LOCAL_INI")" \
    "$(dirname "$STATE_FILE")"


# Fixed-name copies, referenced as login-time defaults in the *.ini files
cp -- "$dark_source" "$dark_target"
cp -- "$light_source" "$light_target"


# Uniquely named copies for the live `gsettings` URIs
# to ensure `gnome-shell` uses the correct files right away
cp -- "$dark_source" "$dark_live_target"
cp -- "$light_source" "$light_live_target"


printf '%s\n' "$dark_source" > "$STATE_FILE"



Background=org.gnome.desktop.background
Screensaver=org.gnome.desktop.screensaver

gsettings set $Background picture-uri-dark "file://$dark_live_target"
gsettings set $Background picture-uri "file://$light_live_target"
gsettings set $Screensaver picture-uri "file://$dark_live_target"



# Persist the unique URIs for `gnome-restore`,
# which loads local/*.ini after the base *.ini files
cat > "$LOCAL_INI" <<EOF
# Written by $(basename "$0") - do not edit

[org/gnome/desktop/background]

picture-uri-dark='file://$dark_live_target'
picture-uri='file://$light_live_target'


[org/gnome/desktop/screensaver]

picture-uri='file://$dark_live_target'
EOF



# Remove the uniquely named copies of previously chosen wallpapers
find "$TARGET_DIR" -name 'dark-tmp-*.jpg' ! -name "dark-tmp-$timestamp.jpg" -delete
find "$TARGET_DIR" -name 'light-tmp-*.jpg' ! -name "light-tmp-$timestamp.jpg" -delete



echo "Installed as: $TARGET_DIR/{dark,light}.jpg"