import torch
import numpy as np

from PIL import Image


def bislerp(samples, width, height):
    def slerp(b1, b2, r):
        '''slerps batches b1, b2 according to ratio r, batches should be flat e.g. NxC'''

        c = b1.shape[-1]

        # norms
        b1_norms = torch.norm(b1, dim=-1, keepdim=True)
        b2_norms = torch.norm(b2, dim=-1, keepdim=True)

        # normalize
        b1_normalized = b1 / b1_norms
        b2_normalized = b2 / b2_norms

        # zero when norms are zero
        b1_normalized[b1_norms.expand(-1, c) == 0.0] = 0.0
        b2_normalized[b2_norms.expand(-1, c) == 0.0] = 0.0

        # slerp
        dot = (b1_normalized * b2_normalized).sum(1)
        omega = torch.acos(dot)
        so = torch.sin(omega)

        # technically not mathematically correct, but more pleasing?
        res = (torch.sin((1.0 - r.squeeze(1)) * omega) / so).unsqueeze(1) * b1_normalized + (torch.sin(r.squeeze(1) * omega) / so).unsqueeze(1) * b2_normalized
        res *= (b1_norms * (1.0 - r) + b2_norms * r).expand(-1, c)

        # edge cases for same or polar opposites
        res[dot > 1 - 1e-5] = b1[dot > 1 - 1e-5]
        res[dot < 1e-5 - 1] = (b1 * (1.0 - r) + b2 * r)[dot < 1e-5 - 1]
        return res

    def generate_bilinear_data(length_old, length_new, device):
        coords_1 = torch.arange(length_old, dtype=torch.float32, device=device).reshape((1, 1, 1, -1))
        coords_1 = torch.nn.functional.interpolate(coords_1, size=(1, length_new), mode="bilinear")
        ratios = coords_1 - coords_1.floor()
        coords_1 = coords_1.to(torch.int64)

        coords_2 = torch.arange(length_old, dtype=torch.float32, device=device).reshape((1, 1, 1, -1)) + 1
        coords_2[:, :, :, -1] -= 1
        coords_2 = torch.nn.functional.interpolate(coords_2, size=(1, length_new), mode="bilinear")
        coords_2 = coords_2.to(torch.int64)
        return ratios, coords_1, coords_2

    orig_dtype = samples.dtype
    samples = samples.float()
    n, c, h, w = samples.shape
    h_new, w_new = (height, width)

    # linear w
    ratios, coords_1, coords_2 = generate_bilinear_data(w, w_new, samples.device)
    coords_1 = coords_1.expand((n, c, h, -1))
    coords_2 = coords_2.expand((n, c, h, -1))
    ratios = ratios.expand((n, 1, h, -1))

    pass_1 = samples.gather(-1, coords_1).movedim(1, -1).reshape((-1, c))
    pass_2 = samples.gather(-1, coords_2).movedim(1, -1).reshape((-1, c))
    ratios = ratios.movedim(1, -1).reshape((-1, 1))

    result = slerp(pass_1, pass_2, ratios)
    result = result.reshape(n, h, w_new, c).movedim(-1, 1)

    # linear h
    ratios, coords_1, coords_2 = generate_bilinear_data(h, h_new, samples.device)
    coords_1 = coords_1.reshape((1, 1, -1, 1)).expand((n, c, -1, w_new))
    coords_2 = coords_2.reshape((1, 1, -1, 1)).expand((n, c, -1, w_new))
    ratios = ratios.reshape((1, 1, -1, 1)).expand((n, 1, -1, w_new))

    pass_1 = result.gather(-2, coords_1).movedim(1, -1).reshape((-1, c))
    pass_2 = result.gather(-2, coords_2).movedim(1, -1).reshape((-1, c))
    ratios = ratios.movedim(1, -1).reshape((-1, 1))

    result = slerp(pass_1, pass_2, ratios)
    result = result.reshape(n, h_new, w_new, c).movedim(-1, 1)
    return result.to(orig_dtype)


def lanczos(samples, width, height):
    images = [Image.fromarray(np.clip(255. * image.movedim(0, -1).cpu().numpy(), 0, 255).astype(np.uint8)) for image in samples]
    images = [image.resize((width, height), resample=Image.Resampling.LANCZOS) for image in images]
    images = [torch.from_numpy(np.array(image).astype(np.float32) / 255.0).movedim(-1, 0) for image in images]
    result = torch.stack(images)
    return result.to(samples.device, samples.dtype)


def adaptive_resize(samples, width, height, upscale_method, crop):
    if crop == "center":
        old_width = samples.shape[3]
        old_height = samples.shape[2]
        old_aspect = old_width / old_height
        new_aspect = width / height
        x = 0
        y = 0
        if old_aspect > new_aspect:
            x = round((old_width - old_width * (new_aspect / old_aspect)) / 2)
        elif old_aspect < new_aspect:
            y = round((old_height - old_height * (old_aspect / new_aspect)) / 2)
        s = samples[:, :, y:old_height - y, x:old_width - x]
    else:
        s = samples

    if upscale_method == "bislerp":
        return bislerp(s, width, height)
    elif upscale_method == "lanczos":
        return lanczos(s, width, height)
    else:
        return torch.nn.functional.interpolate(s, size=(height, width), mode=upscale_method)