"""
Post-export optimization: quantization, TensorRT, and deployment helpers.
"""

import os
from typing import Optional

import torch
import torch.nn as nn


def quantize_model(model: nn.Module, calibration_data=None,
                   method: str = 'dynamic') -> nn.Module:
    """
    Quantize model for faster CPU inference.

    Args:
        model: PyTorch model
        calibration_data: DataLoader for static quantization calibration
        method: 'dynamic' (no calibration needed) or 'static'

    Returns:
        Quantized model
    """
    model.eval().cpu()

    if method == 'dynamic':
        quantized = torch.quantization.quantize_dynamic(
            model,
            {nn.Linear, nn.Conv2d},
            dtype=torch.qint8,
        )
        print("Dynamic quantization complete")
        return quantized

    elif method == 'static':
        if calibration_data is None:
            raise ValueError("Static quantization requires calibration_data")

        model.qconfig = torch.quantization.get_default_qconfig('fbgemm')
        prepared = torch.quantization.prepare(model, inplace=False)

        # Calibrate
        with torch.no_grad():
            for images, _ in calibration_data:
                prepared(images)

        quantized = torch.quantization.convert(prepared, inplace=False)
        print("Static quantization complete")
        return quantized

    else:
        raise ValueError(f"Unknown quantization method: {method}")


def benchmark_deployment(onnx_path: str, input_size: int = 640,
                         num_runs: int = 100) -> dict:
    """
    Benchmark ONNX model inference speed.

    Returns dict with latency and throughput stats.
    """
    import time
    import numpy as np

    try:
        import onnxruntime as ort
    except ImportError:
        return {"error": "onnxruntime not installed"}

    providers = ['CUDAExecutionProvider', 'CPUExecutionProvider']
    session = ort.InferenceSession(onnx_path, providers=providers)

    dummy = np.random.randn(1, 3, input_size, input_size).astype(np.float32)
    input_name = session.get_inputs()[0].name

    # Warmup
    for _ in range(20):
        session.run(None, {input_name: dummy})

    # Benchmark
    latencies = []
    for _ in range(num_runs):
        t0 = time.perf_counter()
        session.run(None, {input_name: dummy})
        latencies.append((time.perf_counter() - t0) * 1000)

    latencies = np.array(latencies)

    return {
        'onnx_path': onnx_path,
        'input_size': input_size,
        'latency_p50_ms': np.percentile(latencies, 50),
        'latency_p95_ms': np.percentile(latencies, 95),
        'fps': 1000 / np.mean(latencies),
        'provider': session.get_providers()[0],
    }


# ──────────────────────── TensorRT Guide ────────────────────────

TENSORRT_GUIDE = """
# TensorRT Optimization Guide for SCRFD

## Prerequisites
pip install tensorrt  # or use NVIDIA TensorRT container

## Convert ONNX to TensorRT Engine

### FP16 (recommended for production GPU deployment)
trtexec --onnx=scrfd_34g.onnx \\
        --saveEngine=scrfd_34g_fp16.engine \\
        --fp16 \\
        --workspace=4096 \\
        --minShapes=input:1x3x640x640 \\
        --optShapes=input:1x3x640x640 \\
        --maxShapes=input:8x3x640x640

### INT8 (fastest, requires calibration)
trtexec --onnx=scrfd_34g.onnx \\
        --saveEngine=scrfd_34g_int8.engine \\
        --int8 \\
        --calib=calibration_cache.bin \\
        --workspace=4096

### Dynamic batch size
trtexec --onnx=scrfd_34g.onnx \\
        --saveEngine=scrfd_34g_dynamic.engine \\
        --fp16 \\
        --minShapes=input:1x3x640x640 \\
        --optShapes=input:4x3x640x640 \\
        --maxShapes=input:16x3x640x640

## Expected Speedups (V100)
| Model      | PyTorch FP32 | ONNX Runtime | TensorRT FP16 | TensorRT INT8 |
|------------|-------------|-------------|----------------|---------------|
| SCRFD-34G  | ~80 FPS     | ~100 FPS    | ~200 FPS       | ~350 FPS      |
| SCRFD-2.5G | ~400 FPS    | ~500 FPS    | ~800 FPS       | ~1200 FPS     |
| SCRFD-0.5G | ~1000 FPS   | ~1200 FPS   | ~2000 FPS      | ~3000 FPS     |

## INT8 Calibration
Use the calibration script:
  python scripts/tensorrt_calibrate.py \\
      --onnx scrfd_34g.onnx \\
      --data-root data/wider_face \\
      --num-images 500

## Deployment with Triton Inference Server
See configs/triton/ for model repository configuration.
"""