# Customization Guide

Advanced customization patterns for your portable NixOS setup.

## Creating Custom Modules

### Pattern 1: Language-Specific Development Environment

Create `nixos/modules/languages/rust.nix`:

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

{
  options.custom.languages.rust.enable = lib.mkEnableOption "Rust development";

  config = lib.mkIf config.custom.languages.rust.enable {
    environment.systemPackages = with pkgs; [
      rustup
      cargo-edit
      cargo-deny
      rust-analyzer
    ];
  };
}
```

Use in `hosts/laptop/default.nix`:
```nix
custom.languages.rust.enable = true;
```

### Pattern 2: Per-Machine Overrides

In `nixos/default.nix`:
```nix
{ config, lib, pkgs, ... }:

{
  options.custom = {
    isLaptop = lib.mkOption { type = lib.types.bool; default = false; };
    isServer = lib.mkOption { type = lib.types.bool; default = false; };
  };

  config = {
    # Settings that only apply to laptops
    power.powertop.enable = lib.mkIf config.custom.isLaptop true;
    services.thermald.enable = lib.mkIf config.custom.isLaptop true;
  };
}
```

In `hosts/laptop/default.nix`:
```nix
custom.isLaptop = true;
```

### Pattern 3: Conditional Package Sets

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

{
  options.custom.tools.enable = lib.mkEnableOption "Extra tools";

  config = lib.mkIf config.custom.tools.enable {
    environment.systemPackages = with pkgs; [
      # Always included
      git
      curl

      # Only if GUI is available
      (lib.optionals (config.custom.hasGui) [
        firefox
        vlc
      ])

      # Only on laptops
      (lib.optionals config.custom.isLaptop [
        powertop
        upower
      ])
    ];
  };
}
```

## Common Customizations

### Add Docker/Podman Support

Edit `nixos/modules/development.nix`:

```nix
virtualisation.podman = {
  enable = true;
  dockerCompat = true;  # Alias docker → podman
};

virtualisation.docker.enable = lib.mkDefault false;
```

### Add Kubernetes Tools

In `nixos/modules/development.nix`:

```nix
languagePackages = {
  # ... existing languages
  kubernetes = with pkgs; [ kubectl helm kustomize ];
};
```

Use in host:
```nix
custom.development.languages = [ "rust" "kubernetes" ];
```

### Add Desktop Environment

Create `nixos/modules/desktop.nix`:

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

{
  options.custom.desktop = {
    enable = lib.mkEnableOption "Desktop environment";
    environment = lib.mkOption {
      type = lib.types.enum [ "gnome" "kde" "xfce" ];
      default = "gnome";
    };
  };

  config = let
    cfg = config.custom.desktop;
  in lib.mkIf cfg.enable {
    services.xserver.enable = true;
    services.xserver.displayManager.gdm.enable = cfg.environment == "gnome";
    services.xserver.desktopManager.gnome.enable = cfg.environment == "gnome";
    
    # Similar for KDE, XFCE...
  };
}
```

Use in host:
```nix
custom.desktop.enable = true;
custom.desktop.environment = "gnome";
```

### Add SSH Server

Edit `nixos/modules/system.nix`:

```nix
services.openssh = {
  enable = lib.mkDefault false;
  ports = [ 22 ];
  settings = {
    PermitRootLogin = "no";
    PasswordAuthentication = false;
  };
};
```

Enable in specific host:
```nix
# hosts/server/default.nix
services.openssh.enable = true;
```

### Add Nginx Web Server

Create `nixos/modules/web.nix`:

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

{
  options.custom.web.enable = lib.mkEnableOption "Web server";

  config = lib.mkIf config.custom.web.enable {
    services.nginx = {
      enable = true;
      virtualHosts."localhost" = {
        listen = [{ addr = "127.0.0.1"; port = 8080; }];
        locations."/".root = "/var/www";
      };
    };
  };
}
```

### Add PostgreSQL Database

Create `nixos/modules/database.nix`:

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

{
  options.custom.database.postgres.enable = lib.mkEnableOption "PostgreSQL";

  config = lib.mkIf config.custom.database.postgres.enable {
    services.postgresql = {
      enable = true;
      ensureDatabases = [ "dev" ];
      ensureUsers = [{
        name = "dev";
        ensureDBOwnership = true;
      }];
    };
  };
}
```

Enable in host:
```nix
custom.database.postgres.enable = true;
```

### Add Docker Containers for Services

Create `nixos/modules/containers.nix`:

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

{
  virtualisation.podman.enable = true;
  
  # Define containers to auto-start
  virtualisation.podman.containers = {
    redis = {
      image = "redis:latest";
      ports = [ "6379:6379" ];
      autoStart = lib.mkDefault false;
    };
  };
}
```

## Home Manager Customizations

### Add Starship Configuration

Edit `home/modules/shell.nix`:

```nix
programs.starship = {
  enable = true;
  settings = {
    add_newline = true;
    character = {
      success_symbol = "[➜](bold green)";
      error_symbol = "[➜](bold red)";
    };
    rust = {
      disabled = false;
      symbol = "🦀 ";
    };
  };
};
```

### Add Zsh Plugins

Edit `home/modules/shell.nix`:

```nix
programs.zsh.plugins = [
  {
    name = "zsh-autosuggestions";
    src = pkgs.fetchFromGitHub { /* ... */ };
  }
  {
    name = "powerlevel10k";
    src = pkgs.fetchFromGitHub { /* ... */ };
    file = "powerlevel10k.zsh-theme";
  }
];
```

### Add VSCode Configuration

Edit `home/modules/editor.nix`:

```nix
programs.vscode = {
  enable = true;
  extensions = with pkgs.vscode-extensions; [
    ms-python.python
    rust-lang.rust-analyzer
    hashicorp.terraform
  ];
  userSettings = {
    "editor.fontSize" = 14;
    "editor.formatOnSave" = true;
    "python.linting.enabled" = true;
  };
};
```

### Add SSH Configuration

Create `home/modules/ssh.nix`:

```nix
{ config, pkgs, ... }:

{
  programs.ssh = {
    enable = true;
    matchBlocks = {
      "github.com" = {
        host = "github.com";
        user = "git";
        identityFile = "~/.ssh/github";
        identitiesOnly = true;
      };
      "*.example.com" = {
        user = "myuser";
        identityFile = "~/.ssh/work";
        forwardAgent = true;
      };
    };
  };
}
```

Import in `home/default.nix`:
```nix
imports = [
  ./modules/ssh.nix
];
```

### Add Tmux Configuration

Edit `home/modules/dev-tools.nix`:

```nix
programs.tmux = {
  enable = true;
  mouse = true;
  baseIndex = 1;
  keyMode = "vi";
  
  plugins = with pkgs.tmuxPlugins; [
    sensible
    vim-tmux-navigator
    resurrect
  ];
  
  extraConfig = ''
    # Custom keybindings
    bind -n M-h select-pane -L
    bind -n M-j select-pane -D
    bind -n M-k select-pane -U
    bind -n M-l select-pane -R
  '';
};
```

## Integration Patterns

### Using Unstable Packages Everywhere

In `home/modules/editor.nix`, use unstable neovim:

```nix
{ pkgs, pkgs-unstable, ... }:

{
  programs.neovim = {
    enable = true;
    package = pkgs-unstable.neovim;
    # ...
  };
}
```

### Conditional Configuration Based on Hardware

In `hosts/laptop/default.nix`:

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

{
  # Laptop-specific
  services.power-profiles-daemon.enable = true;
  services.logind.lidSwitchExternalPower = "ignore";
  
  # Wireless
  networking.wireless.enable = true;

  # Battery
  systemd.services.battery-monitor = {
    description = "Monitor battery health";
    wantedBy = [ "multi-user.target" ];
    script = "${pkgs.acpi}/bin/acpi";
  };
}
```

### Using Secrets in Home Manager

In `home/modules/example.nix`:

```nix
{ config, sops-nix, ... }:

{
  imports = [ sops-nix.homeManagerModules.sops ];

  sops.defaultSopsFile = ../../secrets/secrets.yaml;

  sops.secrets."api/myapi" = {
    path = "%r/myapi";  # In ~/.config/sops-nix
  };

  # Use in programs
  home.sessionVariables.MY_API_KEY = config.sops.secrets."api/myapi".path;
}
```

## Testing Changes Safely

```bash
# Build without applying
home-manager build --flake .#myusername@linux

# Check what will change
sudo nixos-rebuild test --flake .#laptop  # Activates but doesn't add to boot

# Compare with current
sudo nixos-rebuild diff --flake .#laptop

# Rollback if something breaks
nixos-rebuild --rollback switch  # NixOS
home-manager switch --flake .#myusername@linux ~/.local/state/home-manager/current  # HM
```

## Performance Optimization

### Selective Updates

Update only specific inputs:
```bash
nix flake update nixpkgs
nix flake update home-manager
```

### Parallel Builds

In `flake.nix`, speed up evaluation:
```bash
NIX_BUILD_CORES=4 sudo nixos-rebuild switch --flake .#laptop
```

### Binary Cache

Use nixpkgs binary cache:
```nix
# nixos/default.nix
nix = {
  settings = {
    substituters = [ "https://cache.nixos.org" ];
    trusted-public-keys = [ "cache.nixos.org-1:6NCHdD59X431o0gWypQMvvZN1FSVucqL2mGvhiqHIl8=" ];
  };
};
```

See QUICKREF.md for common operations reference.