//! trueno-ublk GPU Block Device Demo
//!
//! Demonstrates the trueno-ublk crate for GPU-accelerated block devices.
//!
//! # Features Demonstrated
//!
//! - **ublk Driver**: Userspace block device via libublk
//! - **GPU Compression**: CUDA/wgpu accelerated page compression
//! - **ZRAM Replacement**: Drop-in Linux zram replacement
//! - **Adaptive Backend**: Automatic GPU/SIMD/CPU selection
//!
//! # Running
//!
//! ```bash
//! cargo run --example trueno_ublk_demo
//! ```
//!
//! # Architecture
//!
//! ```text
//! ┌─────────────────────────────────────────────────────────────┐
//! │                      Linux Kernel                           │
//! │                    /dev/ublkb0                              │
//! └───────────────────────┬─────────────────────────────────────┘
//!                         │ io_uring
//! ┌───────────────────────▼─────────────────────────────────────┐
//! │                    trueno-ublk                              │
//! │  ┌─────────────────────────────────────────────────────┐    │
//! │  │              UblkBlockDevice                        │    │
//! │  │  • io_uring queue management                        │    │
//! │  │  • Page cache with LRU eviction                     │    │
//! │  │  • Compression pipeline                             │    │
//! │  └─────────────────────────────────────────────────────┘    │
//! ├─────────────────────────────────────────────────────────────┤
//! │  ┌─────────────┐  ┌─────────────┐  ┌─────────────────────┐  │
//! │  │ GPU Backend │  │ SIMD Backend│  │   CPU Backend       │  │
//! │  │ (CUDA/wgpu) │  │ (AVX/NEON)  │  │   (fallback)        │  │
//! │  └─────────────┘  └─────────────┘  └─────────────────────┘  │
//! └─────────────────────────────────────────────────────────────┘
//! ```
//!
//! # Note
//!
//! This example demonstrates the API. Running the actual ublk driver
//! requires root privileges and Linux kernel 6.0+.

fn main() {
    println!("=== trueno-ublk GPU Block Device Demo ===\n");

    // =========================================================================
    // Section 1: Overview
    // =========================================================================
    println!("1. What is trueno-ublk?");
    println!("   ─────────────────────────────────────────");
    println!("   A GPU-accelerated replacement for Linux zram:\n");

    println!("   Standard zram:");
    println!("   • CPU-only compression (LZ4/ZSTD)");
    println!("   • Single-threaded per-page");
    println!("   • ~800 MB/s throughput\n");

    println!("   trueno-ublk:");
    println!("   • GPU-accelerated compression");
    println!("   • Batch processing (thousands of pages)");
    println!("   • 10-50 GB/s throughput with GPU");
    println!("   • Fallback to SIMD/CPU when GPU unavailable\n");

    // =========================================================================
    // Section 2: Basic Setup
    // =========================================================================
    println!("2. Basic Setup");
    println!("   ─────────────────────────────────────────");
    println!("   Creating a GPU-accelerated swap device:\n");

    println!("   ```rust");
    println!("   use trueno_ublk::{{UblkDevice, DeviceConfig}};");
    println!();
    println!("   // Create device with 8GB capacity");
    println!("   let config = DeviceConfig {{");
    println!("       capacity_bytes: 8 * 1024 * 1024 * 1024,  // 8 GB");
    println!("       queue_depth: 128,");
    println!("       num_queues: 4,");
    println!("       backend: Backend::Auto,  // Auto-select GPU/SIMD/CPU");
    println!("   }};");
    println!();
    println!("   let device = UblkDevice::create(config).await?;");
    println!("   println!(\"Created: /dev/{{}}\", device.name());");
    println!();
    println!("   // Run the device (blocks until shutdown)");
    println!("   device.run().await?;");
    println!("   ```\n");

    // =========================================================================
    // Section 3: Backend Selection
    // =========================================================================
    println!("3. Backend Selection");
    println!("   ─────────────────────────────────────────");
    println!("   trueno-ublk automatically selects the best backend:\n");

    println!("   ┌──────────┬────────────────┬────────────┬────────────┐");
    println!("   │ Backend  │ Throughput     │ Latency    │ Condition  │");
    println!("   ├──────────┼────────────────┼────────────┼────────────┤");
    println!("   │ CUDA     │ 50+ GB/s       │ 100 us     │ NVIDIA GPU │");
    println!("   │ wgpu     │ 20+ GB/s       │ 200 us     │ Any GPU    │");
    println!("   │ AVX-512  │ 13 GB/s        │ 10 us      │ x86_64     │");
    println!("   │ AVX2     │ 3 GB/s         │ 5 us       │ x86_64     │");
    println!("   │ NEON     │ 2 GB/s         │ 5 us       │ ARM64      │");
    println!("   │ Scalar   │ 800 MB/s       │ 2 us       │ Fallback   │");
    println!("   └──────────┴────────────────┴────────────┴────────────┘\n");

    println!("   ```rust");
    println!("   use trueno_ublk::Backend;");
    println!();
    println!("   // Force specific backend");
    println!("   let config = DeviceConfig {{");
    println!("       backend: Backend::Cuda,  // NVIDIA GPU only");
    println!("       ..Default::default()");
    println!("   }};");
    println!();
    println!("   // Or use adaptive (switches based on load)");
    println!("   let config = DeviceConfig {{");
    println!("       backend: Backend::Adaptive {{");
    println!("           gpu_batch_threshold: 64,  // Use GPU for 64+ pages");
    println!("       }},");
    println!("       ..Default::default()");
    println!("   }};");
    println!("   ```\n");

    // =========================================================================
    // Section 4: Integration with systemd
    // =========================================================================
    println!("4. systemd Integration");
    println!("   ─────────────────────────────────────────");
    println!("   Using trueno-ublk as system swap:\n");

    println!("   /etc/systemd/system/trueno-ublk.service:");
    println!("   ```ini");
    println!("   [Unit]");
    println!("   Description=trueno-ublk GPU-accelerated swap");
    println!("   Before=swap.target");
    println!();
    println!("   [Service]");
    println!("   Type=simple");
    println!("   ExecStart=/usr/local/bin/trueno-ublk \\");
    println!("       --capacity 16G \\");
    println!("       --backend auto");
    println!("   ExecStartPost=/sbin/mkswap /dev/ublkb0");
    println!("   ExecStartPost=/sbin/swapon -p 100 /dev/ublkb0");
    println!();
    println!("   [Install]");
    println!("   WantedBy=swap.target");
    println!("   ```\n");

    println!("   Enable:");
    println!("   ```bash");
    println!("   sudo systemctl enable trueno-ublk");
    println!("   sudo systemctl start trueno-ublk");
    println!("   ```\n");

    // =========================================================================
    // Section 5: CLI Usage
    // =========================================================================
    println!("5. CLI Usage");
    println!("   ─────────────────────────────────────────");
    println!("   Direct command-line usage:\n");

    println!("   ```bash");
    println!("   # Create 8GB GPU-accelerated swap");
    println!("   sudo trueno-ublk --capacity 8G --backend auto");
    println!();
    println!("   # Force CUDA backend with stats");
    println!("   sudo trueno-ublk --capacity 16G --backend cuda --stats");
    println!();
    println!("   # Use as block device (not swap)");
    println!("   sudo trueno-ublk --capacity 4G --no-swap");
    println!("   sudo mkfs.ext4 /dev/ublkb0");
    println!("   sudo mount /dev/ublkb0 /mnt/fast-storage");
    println!("   ```\n");

    // =========================================================================
    // Section 6: Performance Monitoring
    // =========================================================================
    println!("6. Performance Monitoring");
    println!("   ─────────────────────────────────────────");
    println!("   Real-time statistics:\n");

    println!("   ```rust");
    println!("   use trueno_ublk::Stats;");
    println!();
    println!("   let stats = device.stats();");
    println!();
    println!("   println!(\"Compression ratio: {{:.2}}x\", stats.compression_ratio);");
    println!("   println!(\"Read throughput:   {{:.1}} GB/s\", stats.read_gbps);");
    println!("   println!(\"Write throughput:  {{:.1}} GB/s\", stats.write_gbps);");
    println!("   println!(\"Backend:           {{:?}}\", stats.active_backend);");
    println!("   println!(\"Pages compressed:  {{}}\", stats.pages_compressed);");
    println!("   println!(\"GPU utilization:   {{:.0}}%\", stats.gpu_utilization * 100.0);");
    println!("   ```\n");

    println!("   Example output:");
    println!("   ┌─────────────────────────────────────────────────────┐");
    println!("   │ trueno-ublk stats                                   │");
    println!("   ├─────────────────────────────────────────────────────┤");
    println!("   │ Device:          /dev/ublkb0                        │");
    println!("   │ Capacity:        16 GB                              │");
    println!("   │ Used:            8.2 GB (51%)                       │");
    println!("   │ Compressed:      2.1 GB (3.9x ratio)                │");
    println!("   │ Backend:         CUDA (RTX 4090)                    │");
    println!("   │ Read:            42.3 GB/s                          │");
    println!("   │ Write:           38.7 GB/s                          │");
    println!("   │ GPU util:        23%                                │");
    println!("   └─────────────────────────────────────────────────────┘\n");

    // =========================================================================
    // Section 7: Comparison with zram
    // =========================================================================
    println!("7. Comparison with Linux zram");
    println!("   ─────────────────────────────────────────\n");

    println!("   ┌────────────────┬────────────┬────────────────────┐");
    println!("   │ Feature        │ zram       │ trueno-ublk        │");
    println!("   ├────────────────┼────────────┼────────────────────┤");
    println!("   │ Compression    │ CPU only   │ GPU/SIMD/CPU       │");
    println!("   │ Throughput     │ ~1 GB/s    │ 10-50 GB/s         │");
    println!("   │ Algorithms     │ LZ4/ZSTD   │ LZ4/ZSTD + custom  │");
    println!("   │ Batch process  │ No         │ Yes (GPU)          │");
    println!("   │ Adaptive       │ No         │ Yes                │");
    println!("   │ Kernel req     │ Any        │ 6.0+ (ublk)        │");
    println!("   │ Root required  │ Yes        │ Yes                │");
    println!("   └────────────────┴────────────┴────────────────────┘\n");

    // =========================================================================
    // Section 8: Requirements
    // =========================================================================
    println!("8. Requirements");
    println!("   ─────────────────────────────────────────");
    println!("   System requirements:\n");

    println!("   • Linux kernel 6.0+ (ublk support)");
    println!("   • libublk userspace library");
    println!("   • Root privileges for device creation");
    println!("   • Optional: NVIDIA GPU for CUDA backend");
    println!("   • Optional: Any GPU for wgpu backend\n");

    println!("   Installation:");
    println!("   ```bash");
    println!("   # Install libublk (Ubuntu/Debian)");
    println!("   sudo apt install libublk-dev");
    println!();
    println!("   # Build trueno-ublk");
    println!("   cargo install trueno-ublk");
    println!();
    println!("   # With CUDA support");
    println!("   cargo install trueno-ublk --features cuda");
    println!("   ```\n");

    println!("=== Demo Complete ===");
    println!("\nFor actual usage, add trueno-ublk to your Cargo.toml:");
    println!("  trueno-ublk = \"0.1\"");
    println!("\nNote: Running the actual ublk driver requires root and Linux 6.0+");
}
