"""
Two-stage LoRA training: pretrain on synthetic, then fine-tune on the real
688-pair mumble-cleanup dataset.

Stage 1: LoRA pretraining on the 50k synthetic corpus at lr=2e-4.
Stage 2: Resume the stage-1 adapter, fine-tune on the 688 real pairs at
         a much lower lr (2e-5) with fewer iters to avoid overwriting the
         pretraining signal.

Usage:
    python scripts/train_2stage.py
"""

import argparse
import subprocess
import sys
from pathlib import Path


STAGE1_CONFIG = {
    "data": "data/mlx_dataset",
    "adapter_path": "data/models/mumble-cleanup-2stage/stage1_adapters",
    "iters": 2000,
    "batch_size": 4,
    "grad_accumulation": 4,
    "learning_rate": 2e-4,
    "max_seq_length": 1024,
    "steps_per_report": 20,
    "steps_per_eval": 100,
    "save_every": 500,
    "lora_layers": 16,
    "lora_rank": 16,
    "num_lora_train_tokens": 0,  # 0 = lora_rank fine-tuning
}

STAGE2_CONFIG = {
    "data": "data/mlx_dataset_688",
    "adapter_path": "data/models/mumble-cleanup-2stage/stage2_adapters",
    "fused_path": "data/models/mumble-cleanup-2stage/fused",
    "iters": 600,
    "batch_size": 2,
    "grad_accumulation": 8,
    "learning_rate": 2e-5,
    "max_seq_length": 512,
    "steps_per_report": 10,
    "steps_per_eval": 50,
    "save_every": 200,
    "lora_layers": 16,
    "lora_rank": 16,
}


def run(cmd: list[str], cwd: Path):
    print(f"\n$ {' '.join(cmd)}")
    proc = subprocess.run(cmd, cwd=cwd)
    if proc.returncode != 0:
        sys.exit(proc.returncode)


def main():
    parser = argparse.ArgumentParser(description="2-stage LoRA training")
    parser.add_argument("--model", type=str, default="Qwen/Qwen2.5-0.5B-Instruct")
    parser.add_argument("--skip-stage1", action="store_true",
                        help="Skip stage 1 if adapter already exists")
    args = parser.parse_args()

    here = Path(__file__).resolve().parent.parent

    # Stage 1: pretrain on synthetic
    stage1_adapter = here / STAGE1_CONFIG["adapter_path"]
    if args.skip_stage1 and stage1_adapter.exists():
        print(f"Skipping stage 1 (--skip-stage1); using existing adapter at {stage1_adapter}")
    else:
        print("=" * 60)
        print("STAGE 1: pretrain on 50k synthetic")
        print("=" * 60)
        run([
            sys.executable, "-m", "mlx_lm", "lora",
            "--model", args.model,
            "--train",
            "--data", str(here / STAGE1_CONFIG["data"]),
            "--fine-tune-type", "lora",
            "--batch-size", str(STAGE1_CONFIG["batch_size"]),
            "--grad-accumulation-steps", str(STAGE1_CONFIG["grad_accumulation"]),
            "--iters", str(STAGE1_CONFIG["iters"]),
            "--learning-rate", str(STAGE1_CONFIG["learning_rate"]),
            "--steps-per-report", str(STAGE1_CONFIG["steps_per_report"]),
            "--steps-per-eval", str(STAGE1_CONFIG["steps_per_eval"]),
            "--save-every", str(STAGE1_CONFIG["save_every"]),
            "--adapter-path", str(stage1_adapter),
            "--max-seq-length", str(STAGE1_CONFIG["max_seq_length"]),
            "--num-layers", str(STAGE1_CONFIG["lora_layers"]),
            "--seed", "42",
            "--mask-prompt",
        ], cwd=here)

    # Stage 2: fine-tune on 688 real pairs, resume from stage-1 adapter
    print("=" * 60)
    print("STAGE 2: fine-tune on 688 real pairs")
    print("=" * 60)
    stage2_adapter = here / STAGE2_CONFIG["adapter_path"]
    stage2_adapter.mkdir(parents=True, exist_ok=True)
    resume_from = stage1_adapter / "adapters.safetensors"

    run([
        sys.executable, "-m", "mlx_lm", "lora",
        "--model", args.model,
        "--train",
        "--data", str(here / STAGE2_CONFIG["data"]),
        "--fine-tune-type", "lora",
        "--batch-size", str(STAGE2_CONFIG["batch_size"]),
        "--grad-accumulation-steps", str(STAGE2_CONFIG["grad_accumulation"]),
        "--iters", str(STAGE2_CONFIG["iters"]),
        "--learning-rate", str(STAGE2_CONFIG["learning_rate"]),
        "--steps-per-report", str(STAGE2_CONFIG["steps_per_eval"]),
        "--steps-per-eval", str(STAGE2_CONFIG["steps_per_eval"]),
        "--save-every", str(STAGE2_CONFIG["save_every"]),
        "--adapter-path", str(stage2_adapter),
        "--resume-adapter-file", str(resume_from),
        "--max-seq-length", str(STAGE2_CONFIG["max_seq_length"]),
        "--num-layers", str(STAGE2_CONFIG["lora_layers"]),
        "--seed", "43",
        "--mask-prompt",
    ], cwd=here)

    # Fuse stage-2 adapter
    fused = here / STAGE2_CONFIG["fused_path"]
    run([
        sys.executable, "-m", "mlx_lm", "fuse",
        "--model", args.model,
        "--adapter-path", str(stage2_adapter),
        "--save-path", str(fused),
        "--dequantize",
    ], cwd=here)

    print("\n" + "=" * 60)
    print("2-stage training complete")
    print("=" * 60)
    print(f"Stage 1 adapter: {stage1_adapter}")
    print(f"Stage 2 adapter: {stage2_adapter}")
    print(f"Fused model:     {fused}")
    print("\nNext steps:")
    print("  1. Convert to GGUF:")
    print(f"     python ../EchoFlow/Vendor/llama.cpp/convert_hf_to_gguf.py {fused} \\")
    print(f"         --outfile data/models/mumble-cleanup-2stage-f16.gguf")
    print(f"     ../EchoFlow/Vendor/llama.cpp/build-tools/bin/llama-quantize \\")
    print(f"         data/models/mumble-cleanup-2stage-f16.gguf \\")
    print(f"         data/models/mumble-cleanup-2stage-q4km.gguf Q4_K_M")
    print("  2. Evaluate against golden corpus")
    print("  3. Update BonsaiSize.swift with new SHA-256")


if __name__ == "__main__":
    main()