Add example NixOS configuration for lidarr-mb-gap

- Introduced a new configuration file `EXAMPLE_CONFIG.nix` with three examples for setting up the lidarr-mb-gap service on NixOS.
- Included detailed instructions for using flake inputs, direct source paths, and a minimal configuration without VPS sync.
- Provided setup steps for creating environment files, setting permissions, and testing the service after configuration.

nixos/EXAMPLE_CONFIG.nix

@@ -0,0 +1,145 @@
+# ============================================================================
+# Example NixOS Configuration for lidarr-mb-gap
+# ============================================================================
+# 
+# Choose one of the examples below based on your setup:
+# - Example 1: Using flake input (recommended)
+# - Example 2: Using source path directly
+# - Example 3: Minimal configuration
+#
+# ============================================================================
+
+# ============================================================================
+# EXAMPLE 1: Using Flake Input (Recommended)
+# ============================================================================
+# 
+# First, add to your flake.nix inputs:
+#   inputs.lidarr-mb-gap.url = "path:/path/to/lidarr-musicbrainz";
+#   # or
+#   inputs.lidarr-mb-gap.url = "github:yourusername/lidarr-musicbrainz";
+#
+# Then in your NixOS configuration:
+
+{ config, pkgs, inputs, ... }:
+
+{
+  imports = [
+    inputs.lidarr-mb-gap.nixosModules.lidarr-mb-gap
+  ];
+
+  services.lidarr-mb-gap = {
+    enable = true;
+    
+    # Reference the package from the flake
+    package = inputs.lidarr-mb-gap.packages.${pkgs.system}.lidarr-mb-gap;
+    
+    # Report settings
+    reportDir = "/var/lib/lidarr-mb-gap/reports";
+    envFile = "/var/lib/lidarr-mb-gap/.env";
+    runInterval = "daily";  # Options: "daily", "hourly", "*-*-* 02:00:00"
+    
+    # Optional: Auto-sync to VPS
+    syncToVPS = true;
+    vpsHost = "user@vps";  # Your SSH host alias or "user@vps.example.com"
+    vpsPath = "/var/www/html";
+    
+    # SSH configuration for VPS sync
+    sshKeyFile = "/var/lib/lidarr-mb-gap/.ssh/id_ed25519";
+    sshKnownHosts = {
+      vps = {
+        hostNames = [ "vps" "vps.example.com" "1.2.3.4" ];  # All possible hostnames/IPs
+        # Get this with: ssh-keyscan -t ed25519 vps.example.com
+        publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...";
+      };
+    };
+  };
+}
+
+# ============================================================================
+# EXAMPLE 2: Using Source Path (Non-Flake)
+# ============================================================================
+# 
+# If you're not using flakes, import the module directly:
+
+{ config, pkgs, ... }:
+
+{
+  imports = [
+    /path/to/lidarr-musicbrainz/nixos/lidarr-mb-gap.nix
+  ];
+
+  services.lidarr-mb-gap = {
+    enable = true;
+    
+    # Build from source
+    src = /path/to/lidarr-musicbrainz/src;
+    
+    # Report settings
+    reportDir = "/var/lib/lidarr-mb-gap/reports";
+    envFile = "/var/lib/lidarr-mb-gap/.env";
+    runInterval = "daily";
+    
+    # Optional: Auto-sync to VPS
+    syncToVPS = true;
+    vpsHost = "user@vps";
+    vpsPath = "/var/www/html";
+    sshKeyFile = "/var/lib/lidarr-mb-gap/.ssh/id_ed25519";
+    sshKnownHosts = {
+      vps = {
+        hostNames = [ "vps" "vps.example.com" ];
+        publicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...";
+      };
+    };
+  };
+}
+
+# ============================================================================
+# EXAMPLE 3: Minimal Configuration (No VPS Sync)
+# ============================================================================
+
+{ config, pkgs, inputs, ... }:
+
+{
+  imports = [
+    inputs.lidarr-mb-gap.nixosModules.lidarr-mb-gap
+  ];
+
+  services.lidarr-mb-gap = {
+    enable = true;
+    package = inputs.lidarr-mb-gap.packages.${pkgs.system}.lidarr-mb-gap;
+    # All other options use defaults
+  };
+}
+
+# ============================================================================
+# SETUP STEPS AFTER ADDING CONFIGURATION
+# ============================================================================
+#
+# 1. Create the .env file:
+#    sudo mkdir -p /var/lib/lidarr-mb-gap
+#    sudo nano /var/lib/lidarr-mb-gap/.env
+#
+#    Add:
+#    LIDARR_URL=http://your-lidarr-instance:8686
+#    LIDARR_API_KEY=your-api-key-here
+#    SAMBL_URL=https://sambl.lioncat6.com
+#    MAX_ARTISTS=0
+#
+# 2. Set permissions:
+#    sudo chown -R lidarr-mb-gap:lidarr-mb-gap /var/lib/lidarr-mb-gap
+#    sudo chmod 600 /var/lib/lidarr-mb-gap/.env
+#
+# 3. If using VPS sync, set up SSH keys:
+#    sudo -u lidarr-mb-gap ssh-keygen -t ed25519 -f /var/lib/lidarr-mb-gap/.ssh/id_ed25519 -N ""
+#    sudo -u lidarr-mb-gap cat /var/lib/lidarr-mb-gap/.ssh/id_ed25519.pub | ssh user@vps "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
+#    ssh-keyscan -t ed25519 vps.example.com  # Use output in sshKnownHosts
+#
+# 4. Rebuild:
+#    sudo nixos-rebuild switch
+#
+# 5. Test:
+#    sudo systemctl start lidarr-mb-gap
+#    sudo journalctl -u lidarr-mb-gap -f
+#
+# ============================================================================
+