from __future__ import annotations

from pathlib import Path

import numpy as np
import pytest
import torch
from PIL import Image
from torchmetrics.image import PeakSignalNoiseRatio, StructuralSimilarityIndexMeasure


def model_output_dir(parent_dir: Path, model: str) -> Path:
    safe_model_name = model.split("/")[-1].replace(".", "_")
    path = parent_dir / safe_model_name
    path.mkdir(parents=True, exist_ok=True)
    return path


def assert_similarity(
    *,
    model_name: str,
    vllm_image: Image.Image,
    diffusers_image: Image.Image,
    ssim_threshold: float,
    psnr_threshold: float,
    width: int | None = None,
    height: int | None = None,
    compare_mode: str = "RGB",
) -> None:
    requested_size = (width, height) if width is not None and height is not None else None
    if requested_size is not None and diffusers_image.size != requested_size:
        pytest.skip(
            "Skipping as diffusers baseline output is corrupt and not comparable: "
            f"dimensions do not match requested size; requested={requested_size}, got={diffusers_image.size}."
        )

    assert vllm_image.size == diffusers_image.size, (
        f"Online and diffusers output sizes mismatch: online={vllm_image.size}, diffusers={diffusers_image.size}"
    )

    ssim_score, psnr_score = compute_image_ssim_psnr(
        prediction=vllm_image,
        reference=diffusers_image,
        compare_mode=compare_mode,
    )
    print(f"{model_name} similarity metrics:")
    print(f"  SSIM: value={ssim_score:.6f}, threshold>={ssim_threshold:.6f}, range=[-1, 1], higher_is_better=True")
    print(
        f"  PSNR: value={psnr_score:.6f} dB, threshold>={psnr_threshold:.6f} dB, range=[0, +inf), higher_is_better=True"
    )

    assert ssim_score >= ssim_threshold, (
        f"SSIM below threshold for {model_name}: got {ssim_score:.6f}, expected >= {ssim_threshold:.6f}."
    )
    assert psnr_score >= psnr_threshold, (
        f"PSNR below threshold for {model_name}: got {psnr_score:.6f}, expected >= {psnr_threshold:.6f}."
    )


def assert_image_sequence_similarity(
    *,
    model_name: str,
    vllm_images: list[Image.Image],
    diffusers_images: list[Image.Image],
    ssim_threshold: float,
    psnr_threshold: float,
    compare_mode: str = "RGB",
) -> None:
    assert len(vllm_images) == len(diffusers_images), (
        f"Output image count mismatch for {model_name}: online={len(vllm_images)}, diffusers={len(diffusers_images)}"
    )
    for index, (vllm_image, diffusers_image) in enumerate(zip(vllm_images, diffusers_images, strict=True), start=1):
        assert_similarity(
            model_name=f"{model_name}[layer={index}]",
            vllm_image=vllm_image,
            diffusers_image=diffusers_image,
            ssim_threshold=ssim_threshold,
            psnr_threshold=psnr_threshold,
            compare_mode=compare_mode,
        )


def compute_image_ssim_psnr(
    *,
    prediction: Image.Image,
    reference: Image.Image,
    compare_mode: str = "RGB",
) -> tuple[float, float]:
    pred_tensor = _pil_to_batched_tensor(prediction, compare_mode=compare_mode)
    ref_tensor = _pil_to_batched_tensor(reference, compare_mode=compare_mode)

    ssim_metric = StructuralSimilarityIndexMeasure(data_range=1.0)
    psnr_metric = PeakSignalNoiseRatio(data_range=1.0)

    ssim_value = float(ssim_metric(pred_tensor, ref_tensor).item())
    psnr_value = float(psnr_metric(pred_tensor, ref_tensor).item())
    return ssim_value, psnr_value


def _pil_to_batched_tensor(image: Image.Image, *, compare_mode: str) -> torch.Tensor:
    array = np.asarray(image.convert(compare_mode), dtype=np.float32) / 255.0
    tensor = torch.from_numpy(array).permute(2, 0, 1).unsqueeze(0)
    return tensor