nixos/modules/system/stow/default.nix

{...}: {
  flake.nixosModules.stow = {
    config,
    pkgs,
    lib,
    ...
  }: let
    cfg = config.ahmza.stow;

    stowScript = pkgs.writeShellApplication {
      name = "ahmza-stow";
      runtimeInputs = [pkgs.stow pkgs.coreutils pkgs.findutils pkgs.gnused];
      text = ''
        set -euo pipefail

        REPO="${cfg.repoPath}"
        TARGET="$HOME"

        if [ ! -d "$REPO" ]; then
          echo "ahmza-stow: dotfiles repo not found at $REPO; skipping." >&2
          echo "  (clone it with: git clone ${cfg.repoUrl} $REPO)" >&2
          exit 0
        fi

        packages=(${lib.escapeShellArgs cfg.packages})
        if [ ''${#packages[@]} -eq 0 ]; then
          echo "ahmza-stow: no packages configured; nothing to do."
          exit 0
        fi

        cd "$REPO"

        # Back up any existing non-symlink targets that would block stowing $pkg.
        # Mirrors the dotfiles repo's own install script: list the files/links the
        # package provides (relative to the package dir) and back up only real
        # (non-symlink) targets. Skipping symlinks means we never write through an
        # already-stowed folded directory symlink into the repo itself.
        # Backups go to <file>.pre-stow.bak.
        backup_conflicts() {
          local pkg="$1" rel target
          while IFS= read -r rel; do
            target="$HOME/$rel"
            if [ -e "$target" ] && [ ! -L "$target" ]; then
              echo "ahmza-stow: backing up existing $target -> $target.pre-stow.bak"
              mv "$target" "$target.pre-stow.bak"
            fi
          done < <(cd "$REPO/$pkg" && find . \( -type f -o -type l \) | sed 's|^\./||')
        }

        for pkg in "''${packages[@]}"; do
          if [ ! -d "$pkg" ]; then
            echo "ahmza-stow: package '$pkg' not present in repo; skipping." >&2
            continue
          fi

          echo "ahmza-stow: stow -R $pkg"
          # Try to stow first; only back up (and retry) if there's a real conflict.
          if ! stow -R --target="$TARGET" "$pkg" 2>/dev/null; then
            echo "ahmza-stow: conflicts detected for '$pkg'; backing up and retrying."
            backup_conflicts "$pkg"
            if ! stow -R --target="$TARGET" "$pkg"; then
              echo "ahmza-stow: failed to stow '$pkg' — resolve manually." >&2
            fi
          fi
        done

        echo "ahmza-stow: done."
      '';
    };
  in {
    options.ahmza.stow = {
      enable = lib.mkEnableOption "automatic GNU Stow of dotfiles on login";

      user = lib.mkOption {
        type = lib.types.str;
        description = "User whose dotfiles should be stowed.";
      };

      repoPath = lib.mkOption {
        type = lib.types.str;
        default = "/home/${cfg.user}/dot";
        defaultText = "/home/\${config.ahmza.stow.user}/dot";
        description = "Absolute path to the stow dotfiles repository.";
      };

      repoUrl = lib.mkOption {
        type = lib.types.str;
        default = "https://github.com/ahmzaa/dot.git";
        description = "URL of the dotfiles repo (used only in help messages).";
      };

      packages = lib.mkOption {
        type = lib.types.listOf lib.types.str;
        default = [];
        description = ''
          Stow package names (top-level dirs in the dotfiles repo) to link.
          Feature modules append to this via lib.mkAfter / list concatenation.
        '';
      };
    };

    config = lib.mkIf cfg.enable {
      environment.systemPackages = [pkgs.stow stowScript];

      systemd.user.services.ahmza-stow = {
        description = "Stow dotfiles for ${cfg.user}";
        wantedBy = ["default.target"];
        serviceConfig = {
          Type = "oneshot";
          ExecStart = lib.getExe stowScript;
        };
      };
    };
  };
}