{ config, lib, pkgs, ... }:

# ====================== WALLPAPER=========================

let
  # Source of wallpapers in your repo (as you specified)
  srcDir = "~/nixos/files/wallpapers/picture";
  # Note: this is interpreted as a shell-style KEY=VALUE file.
  confFile = "~/nixos/files/conf/wallpaper/wallpaper.conf";
  setWallpaperScript = pkgs.writeShellScript "set-hourly-wallpaper" ''
    set -euo pipefail

    # --- Defaults (can be overridden by wallpaper.conf) ---
    TRANSITION_TYPE="fade"     # e.g. fade, wipe, simple, any
    TRANSITION_DURATION="2"    # seconds (can be decimals)
    TRANSITION_FPS="60"        # frames per second
    SRC_DIR="${srcDir}"

    # Load overrides (shell KEY=VALUE)
    if [ -f "${confFile}" ]; then
      # shellcheck disable=SC1090
      . "${confFile}"
    fi

    DEST_DIR="$HOME/Pictures/Wallpapers"
    mkdir -p "$DEST_DIR"

    # Copy source wallpapers into user's Pictures/Wallpapers
    # -r recursive, -u update if newer
    # If the folder is empty or missing, don't crash the session.
    if [ -d "$SRC_DIR" ]; then
      cp -ru "$SRC_DIR"/. "$DEST_DIR"/ 2>/dev/null || true
    fi

    # Pick a random image from DEST_DIR
    img="$(
      find "$DEST_DIR" -type f \
        \( -iname '*.jpg' -o -iname '*.jpeg' -o -iname '*.png' -o -iname '*.webp' \) \
        | shuf -n 1
    )"

    [ -n "''${img:-}" ] || exit 0

    # Ensure swww daemon is running (per-user)
    if ! ${pkgs.swww}/bin/swww query >/dev/null 2>&1; then
      ${pkgs.swww}/bin/swww-daemon >/dev/null 2>&1 &
      sleep 0.4
    fi

    # Smooth transition wallpaper set
    exec ${pkgs.swww}/bin/swww img "$img" \
      --transition-type "''${TRANSITION_TYPE}" \
      --transition-duration "''${TRANSITION_DURATION}" \
      --transition-fps "''${TRANSITION_FPS}"
  '';
in
{
  # Packages needed by the script + swww
  environment.systemPackages = with pkgs; [
    swww
    bash
    coreutils
    findutils
    util-linux
  ];

  # Run for ANY logged-in user via systemd user units
  # (each user session has its own systemd --user instance)
  systemd.user.services.wallpaper-rotate = {
    description = "Copy wallpapers to ~/Pictures/Wallpapers and set a random wallpaper with transition";
    serviceConfig = {
      Type = "oneshot";
      ExecStart = "${setWallpaperScript}";
    };
  };

  systemd.user.timers.wallpaper-rotate = {
    description = "Hourly wallpaper rotation timer";
    wantedBy = [ "timers.target" ];
    timerConfig = {
      OnBootSec = "2min";
      OnUnitActiveSec = "1h";
      RandomizedDelaySec = "5min";
      Unit = "wallpaper-rotate.service";
    };
  };
}