//! End-to-end LoRA fine-tuning CLI.
//!
//! Scans a directory of `(audio.wav, audio.txt)` pairs, fine-tunes a rank-r
//! LoRA adapter on the backbone q/v projections, saves the adapter as a
//! safetensors file. Then `examples/generate --lora <path>` (Phase 12.4)
//! loads and applies it at inference.
//!
//! Usage:
//!   mkdir /tmp/voice && place foo.wav + foo.txt pairs in there
//!   cargo run -p rtx-csm --release --features metal --example lora_train -- \
//!     --data-dir /tmp/voice --output /tmp/voice.safetensors \
//!     --epochs 5 --rank 8 --alpha 16

use anyhow::Result;
use candle_nn::VarMap;
use clap::Parser;
use rtx_csm::Generator;
use rtx_csm::lora::LoraConfig;
use rtx_csm::training::{
    LoraAdapterMetadata, Trainer, TrainingConfig, TrainingDataset, save_lora_adapter_with_metadata,
};
use std::path::PathBuf;

#[derive(Debug, Parser)]
struct Cli {
    /// Directory containing (.wav, .txt) pairs.
    #[arg(long)]
    data_dir: PathBuf,

    /// Output safetensors path for the trained LoRA adapter.
    #[arg(long)]
    output: PathBuf,

    #[arg(long, default_value_t = 0)]
    speaker: u32,

    #[arg(long, default_value_t = 5)]
    epochs: usize,

    #[arg(long, default_value_t = 8)]
    rank: usize,

    #[arg(long, default_value_t = 16.0)]
    alpha: f32,

    #[arg(long, default_value_t = 5e-4)]
    peak_lr: f64,

    #[arg(long, default_value_t = 1e-5)]
    end_lr: f64,

    #[arg(long, default_value_t = 16)]
    warmup_steps: usize,

    #[arg(long, default_value_t = 1.0)]
    grad_clip: f64,

    /// Frames sampled per training step (1 = one frame per step).
    #[arg(long, default_value_t = 4)]
    frames_per_step: usize,

    #[arg(long, default_value_t = 42)]
    seed: u64,

    #[arg(long)]
    cpu: bool,

    /// Use extended LoRA coverage (q+k+v+output_proj + MLP w1/w2/w3) instead
    /// of the default q+v only. Recommended when fine-tuning on hours of
    /// paired audio for stronger prosody adaptation; the default is safer
    /// when data is scarce (~30 min). Adapter file grows ~6× (still tiny
    /// vs the base model).
    #[arg(long, default_value_t = false)]
    extended_lora: bool,
}

fn main() -> Result<()> {
    tracing_subscriber::fmt().init();
    let cli = Cli::parse();

    let device = if cli.cpu {
        candle_core::Device::Cpu
    } else {
        Generator::default_device()?
    };
    println!("device: {device:?}");

    let mut generator = Generator::load_csm_1b(&device)?;
    println!("model loaded");

    println!("scanning dataset at {}", cli.data_dir.display());
    let dataset = TrainingDataset::load_from_dir(&cli.data_dir, cli.speaker, &mut generator)?;
    println!("dataset: {} examples", dataset.len());

    // Inject LoRA into the backbone. `--extended-lora` opts into the Phase 12.1
    // recipe (q+k+v+output_proj + MLP w1/w2/w3); default keeps q+v only.
    let base = if cli.extended_lora {
        LoraConfig::extended()
    } else {
        LoraConfig::default()
    };
    let lora_cfg = LoraConfig {
        rank: cli.rank,
        alpha: cli.alpha,
        ..base
    };
    println!("LoRA config: target_modules={:?}", lora_cfg.target_modules);
    let vm = VarMap::new();
    generator.model.inner.add_lora_to_backbone(&lora_cfg, &vm)?;
    let n_params: usize = vm.all_vars().iter().map(|v| v.shape().elem_count()).sum();
    println!(
        "LoRA injected: {} trainable params ({} adapter Vars, rank={} alpha={})",
        n_params,
        vm.all_vars().len(),
        cli.rank,
        cli.alpha,
    );

    let train_cfg = TrainingConfig {
        epochs: cli.epochs,
        peak_lr: cli.peak_lr,
        end_lr: cli.end_lr,
        warmup_steps: cli.warmup_steps,
        grad_clip: Some(cli.grad_clip),
        frames_per_step: cli.frames_per_step,
        seed: cli.seed,
    };
    let mut trainer = Trainer::new(&mut generator, &vm, &dataset, train_cfg);
    let losses = trainer.train()?;

    // Print loss curve summary.
    if !losses.is_empty() {
        let n = losses.len();
        let first10: f32 = losses.iter().take(10).sum::<f32>() / 10.0_f32.min(n as f32);
        let last10: f32 = losses.iter().rev().take(10).sum::<f32>() / 10.0_f32.min(n as f32);
        println!(
            "\nloss curve: first 10 avg = {first10:.4}, last 10 avg = {last10:.4}, change = {:+.2}%",
            100.0 * (last10 - first10) / first10
        );
        println!(
            "min={:.4} max={:.4}",
            losses.iter().cloned().fold(f32::INFINITY, f32::min),
            losses.iter().cloned().fold(f32::NEG_INFINITY, f32::max)
        );
    }

    let metadata = LoraAdapterMetadata::from_lora_config(&lora_cfg);
    save_lora_adapter_with_metadata(&vm, &cli.output, &metadata)?;
    println!("\n✓ trained LoRA adapter saved to {}", cli.output.display());
    println!(
        "Use it at inference: examples/generate --lora {} \\\n\
         \t--text \"...\" --out /tmp/out.wav\n\
         (rank/alpha/extended auto-detected from embedded metadata)",
        cli.output.display(),
    );
    Ok(())
}