import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.autograd import Variable

class ChamferLoss(nn.Module):

	def __init__(self):
		super(ChamferLoss, self).__init__()
		self.use_cuda = torch.cuda.is_available()

	def forward(self,preds,gts):
		P = self.batch_pairwise_dist(gts, preds)
		mins, _ = torch.min(P, 1)#[b,n]
		loss_1 = torch.sum(mins)
		mins, _ = torch.min(P, 2)
		loss_2 = torch.sum(mins)

		return loss_1 + loss_2


	def batch_pairwise_dist(self,x,y):
		bs, num_points_x, points_dim = x.size()
		_, num_points_y, _ = y.size()
		xx = torch.bmm(x, x.transpose(2,1))
		yy = torch.bmm(y, y.transpose(2,1))
		zz = torch.bmm(x, y.transpose(2,1))
		if self.use_cuda:
			dtype = torch.cuda.LongTensor
		else:
			dtype = torch.LongTensor
		diag_ind_x = torch.arange(0, num_points_x).type(dtype)
		diag_ind_y = torch.arange(0, num_points_y).type(dtype)
		#brk()
		rx = xx[:, diag_ind_x, diag_ind_x].unsqueeze(1).expand_as(zz.transpose(2,1))
		ry = yy[:, diag_ind_y, diag_ind_y].unsqueeze(1).expand_as(zz)
		P = (rx.transpose(2,1) + ry - 2*zz)
		return P

class GlobalAlignLoss(nn.Module):

	def __init__(self):
		super(GlobalAlignLoss, self).__init__()
		self.use_cuda = torch.cuda.is_available()

	def forward(self,preds,gts, c):
		P = self.batch_pairwise_dist(gts, preds)
		mins, _ = torch.min(P, 1)
		mins = self.huber_loss(mins,c)
		loss_1 = torch.sum(mins)
		mins, _ = torch.min(P, 2)
		mins = self.huber_loss(mins,c)
		loss_2 = torch.sum(mins)

		return loss_1 + loss_2

	def huber_loss(self,x,c):
		x = torch.where(x<c,0.5*(x**2),c*x-0.5*(c**2))
		return x

	def batch_pairwise_dist(self,x,y):
		bs, num_points_x, points_dim = x.size()
		_, num_points_y, _ = y.size()
		xx = torch.bmm(x, x.transpose(2,1))
		yy = torch.bmm(y, y.transpose(2,1))
		zz = torch.bmm(x, y.transpose(2,1))
		if self.use_cuda:
			dtype = torch.cuda.LongTensor
		else:
			dtype = torch.LongTensor
		diag_ind_x = torch.arange(0, num_points_x).type(dtype)
		diag_ind_y = torch.arange(0, num_points_y).type(dtype)
		rx = xx[:, diag_ind_x, diag_ind_x].unsqueeze(1).expand_as(zz.transpose(2,1))
		ry = yy[:, diag_ind_y, diag_ind_y].unsqueeze(1).expand_as(zz)
		P = (rx.transpose(2,1) + ry - 2*zz)
		return P