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

let
  moduleName = "flatpaks";

  # --- Path to your Flatpak list ---
  flatpakConfPath = ./assets/system/apps/flatpaks.conf;

  # --- Read and split file ---
  raw = builtins.readFile flatpakConfPath;
  rawLines = lib.splitString "\n" raw;

  # --- Guard against splitting per character ---
  _guard =
    assert !(builtins.stringLength raw > 1 && builtins.length rawLines == builtins.stringLength raw);
    true;

  # --- Clean each line ---
  cleanLine = line:
    let
      noCR = lib.replaceStrings [ "\r" ] [ "" ] line;
      noComment = lib.head (lib.splitString "#" noCR);
    in
      lib.strings.trim noComment;

  entries = builtins.filter (l: l != "") (map cleanLine rawLines);

  # --- Validate reverse-DNS style ---
  dotCount = s: builtins.length (lib.splitString "." s) - 1;
  isValidId = s: (dotCount s) >= 2;

  _validate = builtins.seq _guard (
    builtins.map (id:
      if isValidId id then true
      else throw ''
        ${moduleName}: invalid Flatpak ID in flatpaks.conf (needs reverse-DNS with at least 2 dots)
        Token         : ${builtins.toJSON id}
        flatpaks.conf : ${toString flatpakConfPath}
        Fix: remove stray tokens or comment them out with '#'.
      ''
    ) entries
  );

  flatpakApps = builtins.seq _validate entries;

  # --- Script to install Flatpaks ---
  syncFlatpaks = pkgs.writeShellScript "sync-flatpaks" ''
    set -euo pipefail

    CONF="/etc/flatpak/flatpaks.conf"
    if [[ -f "$CONF" ]]; then
      echo "flatpak-sync: using $CONF"
    else
      echo "flatpak-sync: WARNING: $CONF not found, using embedded list"
    fi

    if ! flatpak remotes --system --columns=name | grep -qx flathub; then
      flatpak remote-add --system --if-not-exists flathub https://dl.flathub.org/repo/flathub.flatpakrepo
    fi

    desired_apps=(
      ${lib.concatStringsSep " " (map (a: ''"${a}"'') flatpakApps)}
    )

    for app in $desired_apps; do
      if ! flatpak info --system "$app" >/dev/null 2>&1; then
        flatpak install --system -y --noninteractive flathub "$app"
      fi
    done
  '';
in
{
  # --- Top-level toggle ---
  options.enableFlatpaks = lib.mkEnableOption "Enable automatic Flatpak installation";

  # --- Configuration wrapped in mkIf ---
  config = lib.mkIf (config.enableFlatpaks or false) {
    myApps = {
      flatpaks = {
        enable    = true;
        assetsDir = flatpakConfPath;
        files     = entries;
        user      = config.defaultUser or "henrov";
        script    = syncFlatpaks;
      };
    };

    # Enable Flatpak service
    services.flatpak.enable = true;
    xdg.portal.enable = true;

    # Deploy flatpaks.conf to /etc
    environment.etc."flatpak/flatpaks.conf".source = lib.mkForce flatpakConfPath;

    # Systemd service for auto-install
    systemd.services.flatpak-sync = {
      description = "Install Flatpak apps listed in flatpaks.conf";
      wantedBy = [ "multi-user.target" ];
      wants    = [ "network-online.target" ];
      after    = [ "network-online.target" ];

      serviceConfig = {
        Type = "oneshot";
        ExecStart = syncFlatpaks;
      };

      restartTriggers = [ flatpakConfPath ];

      path = [
        pkgs.flatpak
        pkgs.coreutils
        pkgs.gnugrep
        pkgs.gnused
      ];
    };
  };
}