import torch
from core.remesh import calc_face_normals, prepend_dummies


def make_grid(flip: torch.Tensor, device="cuda"):  # HW,2
    H, W = flip.shape
    vertices = torch.zeros(((H + 1) * (W + 1), 3), device=device)
    vertices[:, [1, 0]] = (
        torch.cartesian_prod(torch.arange(0, H + 1), torch.arange(0, W + 1))
        .float()
        .to(device)
    )
    c = (
        (torch.arange(0, W) + (W + 1) * torch.arange(0, H)[:, None])
        .reshape(-1)
        .to(device)
    )  # HW
    faces_right = torch.stack(
        (
            torch.stack((c, c + 1, c + 1 + W + 1), dim=-1),
            torch.stack((c, c + 1 + W + 1, c + W + 1), dim=-1),
        ),
        dim=1,
    )  # HW,2,3
    faces_left = torch.stack(
        (
            torch.stack((c, c + 1, c + W + 1), dim=-1),
            torch.stack((c + 1, c + 1 + W + 1, c + W + 1), dim=-1),
        ),
        dim=1,
    )  # HW,2,3
    faces = torch.where(flip.flipud().reshape(H * W, 1, 1), faces_left, faces_right)
    faces = faces.reshape(H * W * 2, 3)
    return prepend_dummies(vertices, faces)


def area(vertices, faces):
    return calc_face_normals(vertices, faces)[1:, 2].sum().item() / 2